Abadie, J., Abbott, B.P., Abbott, R., Adhikari, R., Ajith, P., Allen, B., Allen, G., Amador Ceron, E., Amin, R.S., Anderson, S.B., Anderson, W.G., Arain, M.A., Araya, M., Aso, Y., Aston, S., Aufmuth, P., Aulbert, C., Babak, S., Baker, P., Ballmer, S., Barker, D., Barr, B., Barriga, P., Barsotti, L., Barton, M.A., Bartos, I., Bassiri, R., Bastarrika, M., Behnke, B., Benacquista, M., Bennett, M.F., Betzwieser, J., Beyersdorf, P.T., Bilenko, I.A., Billingsley, G., Biswas, R., Black, E., Blackburn, J.K., Blackburn, L., Blair, D., Bland, B., Bock, O., Bodiya, T.P., Bondarescu, R., Bork, R., Born, M., Bose, S., Brady, P.R., Braginsky, V.B., Brau, J.E., Breyer, J., Bridges, D.O., Brinkmann, M., Britzger, M., Brooks, A.F., Brown, D.A., Bullington, A., Buonanno, A., Burmeister, O., Byer, R.L., Cadonati, L., Cain, J., Camp, J.B., Cannizzo, J., Cannon, K.C., Cao, J., Capano, C., Cardenas, L., Caudill, S., CavagliàM., Cepeda, C., Chalermsongsak, T., Chalkley, E., Charlton, P., Chatterji, S., Chelkowski, S., Chen, Y., Christensen, N., Chua, S.S.Y., Chung, C.T.Y., Clark, D., Clark, J., Clayton, J.H., Conte, R., Cook, D., Corbitt, T.R.C., Cornish, N., Coward, D., Coyne, D.C., Creighton, J.D.E., Creighton, T.D., Cruise, A.M., Culter, R.M., Cumming, A., Cunningham, L., Dahl, K., Danilishin, S.L., Danzmann, K., Daudert, B., Davies, G., et al., 2011, "Search for gravitational waves associated with the August 2006 timing glitch of the Vela pulsar," Physical Review D, 83, 42001.
The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3×0-21 to 1.4×0-20 on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0×044 to 1.3×045erg.
Adams, E.R., Ló-Morales, M., Elliot, J.L., Seager, S., Osip, D.J., 2011, "Transit Timing Variation Analysis of OGLE-TR-132b with Seven New Transits," The Astrophysical Journal, 728, 125.
We report the results of the first transit timing variation analysis of the very hot Jupiter OGLE-TR-132b, using 10 transits collected over a seven-year period. Our analysis combines three previously published transit light curves with seven new transits, which were observed between 2008 February and 2009 May with the new MagIC-e2V instrument on the Magellan Telescopes in Chile. We provide a revised planetary radius of Rp= 1.23 ± 0.07RJ , which is slightly larger, but consistent within the errors, than that given by previously published results. Analysis of the planet-to-star radius ratio, orbital separation, inclination, and transit duration reveals no apparent variation in any of those parameters during the time span observed. We also find no sign of transit timing variations larger than -108 ± 49 s, with most residuals very close to zero. This allows us to place an upper limit of 5-10 M⊕ for a coplanar, low-eccentricity perturber in either the 2:1 or 3:2 mean-motion resonance with OGLE-TR-132b. We similarly find that the data are entirely consistent with a constant orbital period and there is no evidence for orbital decay within the limits of precision of our data. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
Altamimi, Z., Collilieux, X., Mévier, L., 2011, "ITRF2008: an improved solution of the international terrestrial reference frame," Journal of Geodesy, 7.
ITRF2008 is a refined version of the International Terrestrial Reference Frame based on reprocessed solutions of the four space geodetic techniques: VLBI, SLR, GPS and DORIS, spanning 29, 26, 12.5 and 16 years of observations, respectively. The input data used in its elaboration are time series (weekly from satellite techniques and 24-h session-wise from VLBI) of station positions and daily Earth Orientation Parameters (EOPs). The ITRF2008 origin is defined in such a way that it has zero translations and translation rates with respect to the mean Earth center of mass, averaged by the SLR time series. Its scale is defined by nullifying the scale factor and its rate with respect to the mean of VLBI and SLR long-term solutions as obtained by stacking their respective time series. The scale agreement between these two technique solutions is estimated to be 1.05 ± 0.13 ppb at epoch 2005.0 and 0.049 ± 0.010 ppb/yr. The ITRF2008 orientation (at epoch 2005.0) and its rate are aligned to the ITRF2005 using 179 stations of high geodetic quality. An estimate of the origin components from ITRF2008 to ITRF2005 (both origins are defined by SLR) indicates differences at epoch 2005.0, namely: -0.5, -0.9 and -4.7 mm along X, Y and Z-axis, respectively. The translation rate differences between the two frames are zero for Y and Z, while we observe an X-translation rate of 0.3 mm/yr. The estimated formal errors of these parameters are 0.2 mm and 0.2 mm/yr, respectively. The high level of origin agreement between ITRF2008 and ITRF2005 is an indication of an imprecise ITRF2000 origin that exhibits a Z-translation drift of 1.8 mm/yr with respect to ITRF2005. An evaluation of the ITRF2008 origin accuracy based on the level of its agreement with ITRF2005 is believed to be at the level of 1 cm over the time-span of the SLR observations. Considering the level of scale consistency between VLBI and SLR, the ITRF2008 scale accuracy is evaluated to be at the level of 1.2 ppb (8 mm at the equator) over the common time-span of the observations of both techniques. Although the performance of the ITRF2008 is demonstrated to be higher than ITRF2005, future ITRF improvement resides in improving the consistency between local ties in co-location sites and space geodesy estimates.
Archinal, B.A., A'Hearn, M.F., Bowell, E., Conrad, A., Consolmagno, G.J., Courtin, R., Fukushima, T., Hestroffer, D., Hilton, J.L., Krasinsky, G.A., Neumann, G., Oberst, J., Seidelmann, P.K., Stooke, P., Tholen, D.J., Thomas, P.C., Williams, I.P., 2011, "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009," Celestial Mechanics and Dynamical Astronomy, 109, 101-135.
Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars' satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) .teins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.
Batalha, N.M., Borucki, W.J., Bryson, S.T., Buchhave, L.A., Caldwell, D.A., Christensen-Dalsgaard, J., Ciardi, D., Dunham, E.W., Fressin, F., Gautier, T.N., Gilliland, R.L., Haas, M.R., Howell, S.B., Jenkins, J.M., Kjeldsen, H., Koch, D.G., Latham, D.W., Lissauer, J.J., Marcy, G.W., Rowe, J.F., Sasselov, D.D., Seager, S., Steffen, J.H., Torres, G., Basri, G.S., Brown, T.M., Charbonneau, D., Christiansen, J., Clarke, B., Cochran, W.D., Dupree, A., Fabrycky, D.C., Fischer, D., Ford, E.B., Fortney, J., Girouard, F.R., Holman, M.J., Johnson, J., Isaacson, H., Klaus, T.C., Machalek, P., Moorehead, A.V., Morehead, R.C., Ragozzine, D., Tenenbaum, P., Twicken, J., Quinn, S., VanCleve, J., Walkowicz, L.M., Welsh, W.F., Devore, E., Gould, A., 2011, "Kepler's First Rocky Planet: Kepler-10b," The Astrophysical Journal, 729, 27.
NASA's Kepler Mission uses transit photometry to determine the frequency of Earth-size planets in or near the habitable zone of Sun-like stars. The mission reached a milestone toward meeting that goal: the discovery of its first rocky planet, Kepler-10b. Two distinct sets of transit events were detected: (1) a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris T [BJD] =2454964.57375+0.00060 -0.00082 + N*0.837495+0.000004 -0.000005 days and (2) a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris T [BJD] =2454971.6761+0.0020 -0.0023 + N*45.29485+0.00065 -0.00076 days. Statistical tests on the photometric and pixel flux time series established the viability of the planet candidates triggering ground-based follow-up observations. Forty precision Doppler measurements were used to confirm that the short-period transit event is due to a planetary companion. The parent star is bright enough for asteroseismic analysis. Photometry was collected at 1 minute cadence for >4 months from which we detected 19 distinct pulsation frequencies. Modeling the frequencies resulted in precise knowledge of the fundamental stellar properties. Kepler-10 is a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence star with T eff = 5627 ± 44 K, M sstarf = 0.895 ± 0.060 M sun, and R sstarf = 1.056 ± 0.021 R sun. Physical models simultaneously fit to the transit light curves and the precision Doppler measurements yielded tight constraints on the properties of Kepler-10b that speak to its rocky composition: M P = 4.56+1.17 -1.29 M ⊕, R P = 1.416+0.033 -0.036 R ⊕, and ρP = 8.8+2.1 -2.9 g cm-3. Kepler-10b is the smallest transiting exoplanet discovered to date.
Berdyugina, S.V., Berdyugin, A.V., Fluri, D.M., Piirola, V., 2011, "Polarized Reflected Light from the Exoplanet HD189733b: First Multicolor Observations and Confirmation of Detection," The Astrophysical Journal, 728, L6.
We report the first multicolor polarimetric measurements (UBV bands) for the hot Jupiter HD189733b and confirm our previously reported detection of polarization in the B band. The wavelength dependence of polarization indicates the dominance of Rayleigh scattering with a peak in the blue B and U bands of ~10-4 ± 10-5 and at least a factor of two lower signal in the V band. The Rayleigh-like wavelength dependence, also detected in the transmitted light during transits, implies a rapid decrease of the polarization signal toward longer wavelengths. Therefore, the nondetection by Wiktorowicz, based on a measurement integrated within a broad passband covering the V band and partly covering the B and R bands, is inconclusive and consistent with our detection in B. We discuss possible sources of the polarization and demonstrate that effects of incomplete cancellation of stellar limb polarization due to starspots or tidal perturbations are negligible as compared with scattering polarization in the planetary atmosphere. We compare the observations with a Rayleigh-Lambert model and determine effective radii and geometrical albedos for different wavelengths. We find a close similarity of the wavelength-dependent geometrical albedo with that of the Neptune atmosphere, which is known to be strongly influenced by Rayleigh and Raman scattering. Our result establishes polarimetry as a reliable means for directly studying exoplanetary atmospheres.
Beuermann, K., Buhlmann, J., Diese, J., Dreizler, S., Hessman, F.V., Husser, T.-O., Miller, G.F., Nickol, N., Pons, R., Ruhr, D., Schmü, H., Schwope, A.D., Sorge, T., Ulrichs, L., Winget, D.E., Winget, K.I., 2011, "The giant planet orbiting the cataclysmic binary DP Leonis," Astronomy and Astrophysics, 526, 53.
Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution, especially for the yet nearly unexplored class of circumbinary planets. We searched for such planets in DP Leo, an eclipsing short-period binary, which shows long-term eclipse-time variations. Using published, reanalysed, and new mid-eclipse times of the white dwarf in DP Leo, obtained between 1979 and 2010, we find agreement with the light-travel-time effect produced by a third body in an elliptical orbit. In particular, the measured binary period in 2009/2010 and the implied radial velocity coincide with the values predicted for the motion of the binary and the third body around the common center of mass. The orbital period, semi-major axis, and eccentricity of the third body are Pc = 28.0 ± 2.0 yrs, ac = 8.2 ± 0.4 AU, and ec = 0.39 ± 0.13. Its mass of sin ic Mc = 6.1 ± 0.5 MJup qualifies it as a giant planet. It formed either as a first generation object in a protoplanetary disk around the original binary or as a second generation object in a disk formed in the common envelope shed by the progenitor of the white dwarf. Even a third generation origin in matter lost from the present accreting binary can not be entirely excluded. We searched for, but found no evidence for a fourth body.
Bizouard, C., Remus, F., Lambert, S.B., Seoane, L., Gambis, D., 2011, "The Earth's variable Chandler wobble," Astronomy and Astrophysics, 526, 106.
Aims: We investigated the causes of the Earth's Chandler wobble variability over the past 60 years. Our approach is based on integrating of the atmospheric and oceanic angular momentum computed by global circulation models. We directly compared the result of the integration with the Earth's pole coordinate observed by precise astrometric, space, and geodetic techniques. This approach differs from the traditional approach in which the observed polar motion is transformed into a so-called geodetic excitation function, and compared afterwards with the angular momentum of the external geophysical fluid layers.
Methods: In the time domain, we integrated the atmospheric angular momentum time series from the National Center for Environmental Prediction/National Center for Atmospheric Research Reanalysis project and the oceanic angular momentum data from the ECCO consortium. We extracted the Chandler wobble from this modeled polar motion by singular spectrum analysis, and compared it with the Chandler wobble extracted from the observed polar motion given by the International Earth Rotation and Reference Systems Service data.
Results: We showed that the combination of the atmosphere and the oceans explains most of the observed Chandler wobble variations, and is consistent with results reported in the literature and obtained with the traditional approach. Our approach allows one to appreciate the separate contributions of the atmosphere and the oceans to the various bumps and valleys observed in the Chandler wobble. Though the atmosphere explains the Chandler wobble amplitude variations between 1949 and 1970, the reexcitation of the Chandler wobble that begins in the 1980s, after a minimum around 1970, and that reaches its maximum in the late 1990s is due to the oceans, while the atmospheric contribution remains stable within the same period.
Borucki, W.J., Koch, D.G., Basri, G., Batalha, N., Boss, A., Brown, T.M., Caldwell, D., Christensen-Dalsgaard, J., Cochran, W.D., DeVore, E., Dunham, E.W., Dupree, A.K., Gautier, T.N., III, Geary, J.C., Gilliland, R., Gould, A., Howell, S.B., Jenkins, J.M., Kjeldsen, H., Latham, D.W., Lissauer, J.J., Marcy, G.W., Monet, D.G., Sasselov, D., Tarter, J., Charbonneau, D., Doyle, L., Ford, E.B., Fortney, J., Holman, M.J., Seager, S., Steffen, J.H., Welsh, W.F., Allen, C., Bryson, S.T., Buchhave, L., Chandrasekaran, H., Christiansen, J.L., Ciardi, D., Clarke, B.D., Dotson, J.L., Endl, M., Fischer, D., Fressin, F., Haas, M., Horch, E., Howard, A., Isaacson, H., Kolodziejczak, J., Li, J., MacQueen, P., Meibom, S., Prsa, A., Quintana, E.V., Rowe, J., Sherry, W., Tenenbaum, P., Torres, G., Twicken, J.D., Van Cleve, J., Walkowicz, L., Wu, H., 2011, "Characteristics of Kepler Planetary Candidates Based on the First Data Set," The Astrophysical Journal, 728, 117.
In the spring of 2009, the Kepler Mission commenced high-precision photometry on nearly 156,000 stars to determine the frequency and characteristics of small exoplanets, conduct a guest observer program, and obtain asteroseismic data on a wide variety of stars. On 2010 June 15, the Kepler Mission released most of the data from the first quarter of observations. At the time of this data release, 705 stars from this first data set have exoplanet candidates with sizes from as small as that of Earth to larger than that of Jupiter. Here we give the identity and characteristics of 305 released stars with planetary candidates. Data for the remaining 400 stars with planetary candidates will be released in 2011 February. More than half the candidates on the released list have radii less than half that of Jupiter. Five candidates are present in and near the habitable zone; two near super-Earth size, and three bracketing the size of Jupiter. The released stars also include five possible multi-planet systems. One of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates with near-resonant periods.
Bourda, G., Collioud, A., Charlot, P., Porcas, R., Garrington, S., 2011, "VLBI observations of optically-bright extragalactic radio sources for the alignment of the radio frame with the future Gaia frame. II. Imaging candidate sources," Astronomy and Astrophysics, 526, 102.
Context. The European space astrometry mission Gaia, to be launched by 2012, will construct a dense optical QSO-based celestial reference frame which will need to be linked to the International Celestial Reference Frame (ICRF; the IAU fundamental frame), with the highest accuracy. However, it has been found that only 10% of the ICRF sources (70 sources) are suitable to establish this link. The remaining sources are not useful either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy.
Aims: In order to improve the accuracy of this alignment, we have developed a program of VLBI observations based on three steps to detect, image and measure astrometric positions of weak extragalactic radio sources, with bright optical counterparts, from a sample of 447 candidate sources. <BR /> Methods: The experiments devoted to VLBI detection, carried out with the European VLBI Network (EVN) in June and October 2007, were very successful, with 398 sources detected at both S- and X-bands. From these, 105 sources were observed in March 2008 with a global VLBI array (EVN and VLBA; Very Long Baseline Array) for imaging their VLBI structures.
Results: All sources were successfully imaged in both bands and about 50% (47 sources) were found to be point-like on VLBI scales. These images are available at http://www.obs.u-bordeaux1.fr/BVID/GC030. VLBI positions of these sources will be measured accurately in future astrometric experiments. Full Table 3 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via "http://cdsweb.u-strasbg.fr/viz-bin/qcat?J/A+A/526/A102
Braccini, S., Cella, G., Ferrante, I., Passuello, D., Torre, O., 2011, "Resampling technique to correct for the Doppler effect in a search for gravitational waves," Physical Review D, 83, 44033.
The frequency of any gravitational-wave signal received from a spinning neutron star will appear Doppler-shifted by the Earth.s rotation and orbital motion. This frequency shift must be compensated to recover the signal energy as a spectral monochromatic peak with a high signal-to-noise ratio. Generally the correction depends on the source.s position in the sky, spin, and spin-down rate. Here we propose a method of applying a single correction to the data which is valid for all the emission frequencies at a fixed position in the sky and for a given spin-down rate. We advance or retard the antenna proper time by removing (or repeating) single samples of the digitized output signal to keep the effective receiver and source clocks in accurate synchronization. The method, which requires just a few lines of code and little computational effort, appears to be very effective for .semitargeted. searches, where the source direction is known but the emission frequency is not.
Breiter, S., Vokrouhlický 2011, "Yarkovsky-O'Keefe-Radzievskii-Paddack effect with anisotropic radiation," Monthly Notices of the Royal Astronomical Society, 410, 2807-2816.
In this paper, we study the influence of optical scattering and thermal radiation models on the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. The Lambertian formulation is compared with the scattering and emission laws and Lommel-Seeliger reflection. Although the form of the reflectivity function strongly influences the mean torques because of scattering or thermal radiation alone, their combined contribution to the rotation period YORP effect is not very different from the standard Lambertian values. For higher albedo values, the differences between the Hapke and Lambert models become significant for the YORP effect in attitude.
Brumberg, V.A., Ivanova, T.V., 2011, "On constructing the general Earth's rotation theory," Celestial Mechanics and Dynamical Astronomy, 8.
In the present paper the equations of the orbital motion of the major planets and the Moon and the equations of the three.axial rigid Earth.s rotation in Euler parameters are reduced to the secular system describing the evolution of the planetary and lunar orbits (independent of the Earth.s rotation) and the evolution of the Earth.s rotation (depending on the planetary and lunar evolution). Hence, the theory of the Earth.s rotation can be presented by means of the series in powers of the evolutionary variables with quasi-periodic coefficients with respect to the planetary.lunar mean longitudes. This form of the Earth.s rotation problem is compatible with the general planetary theory involving the separation of the short.period and long.period variables and avoiding the appearance of the non.physical secular terms.
Budaj, J., 2011, "The Reflection Effect in Interacting Binaries or in Planet-Star Systems," The Astronomical Journal, 141, 59.
There are many similarities between interacting binary stars and stars with a close-in giant extrasolar planet. The reflection effect is a well-known example. Although the generally accepted treatment of this effect in interacting binaries is successful in fitting light curves of eclipsing binaries, it is not very suitable for studying cold objects irradiated by hot objects or extrasolar planets. The aim of this paper is to develop a model of the reflection effect which could be easily incorporated into the present codes for modeling of interacting binaries so that these can be used to study the aforementioned objects. Our model of the reflection effect takes into account the reflection (scattering), heating, and heat redistribution over the surface of the irradiated object. The shape of the object is described by the non-spherical Roche potential expected for close objects. Limb and gravity darkening are included in the calculations of the light output from the system. The model also accounts for the orbital revolution and rotation of the exoplanet with appropriate Doppler shifts for the scattered and thermal radiation. Subsequently, light curves and/or spectra of several exoplanets have been modeled and the effects of the heat redistribution, limb darkening/brightening, (non-)gray albedo, and non-spherical shape have been studied. Recent observations of planet-to-star flux ratio of HD189733b, WASP12b, and WASP-19b at various phases were reproduced with very good accuracy. It was found that HD189733b has a low Bond albedo and intense heat redistribution, while WASP-19b has a low Bond albedo and low heat redistribution. The exact Roche geometries and temperature distributions over the surface of all 78 transiting extrasolar planets have been determined. Departures from the spherical shape may vary considerably but departures of about 1% in the radius are common within the sample. In some cases, these departures can reach 8%, 12%, or 14%, for WASP-33b, WASP-19b, and WASP-12b, respectively. The mean temperatures of these planets also vary considerably from 300 K to 2600 K. The extreme cases are WASP-18b, WASP-12b, and WASP-33b, with mean temperatures of 2330 K, 2430 K, and 2600 K, respectively.
Burt, B.J., Lommen, A.N., Finn, L.S., 2011, "Optimizing Pulsar Timing Arrays to Maximize Gravitational Wave Single-source Detection: A First Cut," The Astrophysical Journal, 730, 17.
Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves (GWs) in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on (1) the direction of the GW source, (2) the timing accuracy of the pulsars in the array, and (3) how the available observing time is allocated among those pulsars. Here, we present a simple way to calculate the sensitivity of the PTA as a function of direction of a single GW source, based only on the location and root-mean-square residual of the pulsars in the array. We use this calculation to suggest future strategies for the current North American Nanohertz Observatory for Gravitational Waves PTA in its goal of detecting single GW sources. We also investigate the effects of an additional pulsar on the array sensitivity, with the goal of suggesting where PTA pulsar searches might be best directed. We demonstrate that, in the case of single GW sources, if we are interested in maximizing the volume of space to which PTAs are sensitive, there exists a slight advantage to finding a new pulsar near where the array is already most sensitive. Further, the study suggests that more observing time should be dedicated to the already low-noise pulsars in order to have the greatest positive effect on the PTA sensitivity. We have made a Web-based sensitivity mapping tool available.
Campo, C.J., Harrington, J., Hardy, R.A., Stevenson, K.B., Nymeyer, S., Ragozzine, D., Lust, N.B., Anderson, D.R., Collier-Cameron, A., Blecic, J., Britt, C.B.T., Bowman, W.C., Wheatley, P.J., Loredo, T.J., Deming, D., Hebb, L., Hellier, C., Maxted, P.F.L., Pollaco, D., West, R.G., 2011, "On the Orbit of Exoplanet WASP-12b," The Astrophysical Journal, 727, 125.
We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity, leading to an estimate of the tidal Love number and an assessment of the degree of central concentration in the planetary interior. An initial ground-based secondary-eclipse phase reported by Ló-Morales et al. (0.510 ± 0.002) implied eccentricity at the 4.5σ level. The spectroscopic orbit of Hebb et al. has eccentricity 0.049 ± 0.015, a 3σ result, implying an eclipse phase of 0.509 ± 0.007. However, there is a well-documented tendency of spectroscopic data to overestimate small eccentricities. Our eclipse phases are 0.5010 ± 0.0006 (3.6 and 5.8 μm) and 0.5006 ± 0.0007 (4.5 and 8.0 μm). An unlikely orbital precession scenario invoking an alignment of the orbit during the Spitzer observations could have explained this apparent discrepancy, but the final eclipse phase of Ló-Morales et al. (0.510 ±+0.007 -0.006) is consistent with a circular orbit at better than 2σ. An orbit fit to all the available transit, eclipse, and radial-velocity data indicates precession at <1σ a non-precessing solution fits better. We also comment on analysis and reporting for Spitzer exoplanet data in light of recent re-analyses.
Celikel, O., 2011, "Application of the vector modulation method to the north finder capability gyroscope as a directional sensor," Measurement Science and Technology, 22, 5203.
This paper presents the application of the vector modulation method (VMM) to an open-loop interferometric fiber optic gyroscope, called the north finder capability gyroscope (NFCG), designed and assembled in TUBITAK UME (National Metrology Institute of Turkey). The method contains a secondary modulation/demodulation circuit with an AD630 chip, depending on the periodic variation of the orientation of the sensing coil sensitive surface vector with respect to geographic north at a laboratory latitude and collection of dc voltage at the secondary demodulation circuit output in the time domain. The resultant dc voltage proportional to the first-kind Bessel function based on Sagnac phase shift for the first order is obtained as a result of vector modulation together with the Earth's rotation. A new model function is developed and introduced to evaluate the angular errors of the NFCG with VMM in finding geographic north.
Chung, S.-J., Lee, C.-U., 2011, "Properties of the planetary caustic perturbation," Monthly Notices of the Royal Astronomical Society, 411, 151-154.
Just two of 10 extrasolar planets found by microlensing have been detected by the planetary caustic, despite the higher probability of planet detection relative to the central caustic, which has been responsible for four extrasolar planet detections. This is because the perturbations induced by the planetary caustic are unpredictable, thus making it difficult to carry out strategic observations. However, if future high-cadence monitoring surveys are conducted, the majority of planetary caustic events including the events by free-floating planets and wide-separation planets would be detected. Hence, understanding the planetary caustic perturbations becomes important. In this paper, we investigate in detail the pattern of the planetary caustic perturbations. From this study, we find three properties of the planetary caustic perturbations. First, planetary systems with the same star.planet separation (s) basically produce perturbations of constant strength, regardless of the planet-to-star mass ratio (q), but the duration of each perturbation scales with . Secondly, close planetary systems with the same separation produce essentially the same negative perturbations between two triangular-shaped caustics, regardless of q, but the duration of the perturbations scales with . Thirdly, the positive perturbations for planetary systems with the same mass ratio become stronger as the caustic shrinks with the increasing |log s|, while the negative perturbations become weaker. We estimate the degeneracy in the determination of q that occurs in planetary caustic events. From this, we find that the mass ratio can be more precisely determined as q increases and |log s| decreases. We also find that the degeneracy range of events for which the source star passes close to the planetary caustic is usually very narrow, and thus it would not significantly affect the determination of q.
de Marco, O., Passy, J.-C., Moe, M., Herwig, F., Mac Low, M.-M., Paxton, B., 2011, "On the a formalism for the common envelope interaction," Monthly Notices of the Royal Astronomical Society, 411, 2277-2292.
The α formalism is a common way to parametrize the common envelope interaction between a giant star and a more compact companion. The α parameter describes the fraction of orbital energy released by the companion that is available to eject the giant star's envelope. By using new, detailed stellar evolutionary calculations, we derive a user-friendly prescription for the λ parameter and an improved approximation for the envelope binding energy, thus revising the α equation. We then determine α both from simulations and from observations in a self-consistent manner. By using our own stellar structure models as well as population considerations to reconstruct the primary's parameters at the time of the common envelope interaction, we gain a deeper understanding of the uncertainties. We find that systems with very low values of q (the ratio of the companion's mass to the mass of the primary at the time of the common envelope interaction) have higher values of α. A fit to the data suggests that lower-mass companions are left at comparable or larger orbital separations to more massive companions. We conjecture that lower-mass companions take longer than a stellar dynamical time to spiral into the giant's core, and that this is key to allowing the giant to use its own thermal energy to help unbind its envelope. As a result, although systems with light companions might not have enough orbital energy to unbind the common envelope, they might stimulate a stellar reaction that results in the common envelope ejection.
Dominik, M., 2011, "Planetary mass function and planetary systems," Monthly Notices of the Royal Astronomical Society, 411, 2-8.
With planets orbiting stars, a planetary mass function should not be seen as a low-mass extension of the stellar mass function, but a proper formalism needs to take care of the fact that the statistical properties of planet populations are linked to the properties of their respective host stars. This can be accounted for by describing planet populations by means of a differential planetary mass-radius-orbit function, which together with the fraction of stars with given properties that are orbited by planets and the stellar mass function allows the derivation of all statistics for any considered sample. These fundamental functions provide a framework for comparing statistics that result from different observing techniques and campaigns which all have their very specific selection procedures and detection efficiencies. Moreover, recent results both from gravitational microlensing campaigns and radial-velocity surveys of stars indicate that planets tend to cluster in systems rather than being the lonely child of their respective parent star. While planetary multiplicity in an observed system becomes obvious with the detection of several planets, its quantitative assessment however comes with the challenge to exclude the presence of further planets. Current exoplanet samples begin to give us first hints at the population statistics, whereas pictures of planet parameter space in its full complexity call for samples that are 2-4 orders of magnitude larger. In order to derive meaningful statistics, however, planet detection campaigns need to be designed in such a way that well-defined fully deterministic target selection, monitoring and detection criteria are applied. The probabilistic nature of gravitational microlensing makes this technique an illustrative example of all the encountered challenges and uncertainties.
Fischetti, S., Healy, J., Cadonati, L., London, L., Mohapatra, S.R.P., Shoemaker, D., 2011, "Exploring the use of numerical relativity waveforms in burst analysis of precessing black hole mergers," Physical Review D, 83, 44019.
Recent years have witnessed tremendous progress in numerical relativity and an ever improving performance of ground-based interferometric gravitational wave detectors. In preparation for the Advanced Laser Interferometer Gravitational Wave Observatory (Advanced LIGO) and a new era in gravitational wave astronomy, the numerical relativity and gravitational wave data analysis communities are collaborating to ascertain the most useful role for numerical relativity waveforms in the detection and characterization of binary black hole coalescences. In this paper, we explore the detectability of equal mass, merging black hole binaries with precessing spins and total mass MT∈[80,350]Mȯ, using numerical relativity waveforms and templateless search algorithms designed for gravitational wave bursts. In particular, we present a systematic study using waveforms produced by the MayaKranc code that are added to colored, Gaussian noise and analyzed with the Omega burst search algorithm. Detection efficiency is weighed against the orientation of one of the black-hole.s spin axes. We find a strong correlation between the detection efficiency and the radiated energy and angular momentum, and that the inclusion of the ℓ=2, m=±1, 0 modes, at a minimum, is necessary to account for the full dynamics of precessing systems.
Fomalont, E., Johnston, K., Fey, A., Boboltz, D., Oyama, T., Honma, M., 2011, "The Position/Structure Stability of Four ICRF2 Sources," The Astronomical Journal, 141, 91.
Four close radio sources in the International Celestial Reference Frame (ICRF) catalog were observed using phase referencing with the VLBA at 43, 23, and 8.6 GHz, and with VERA at 23 GHz over a one-year period. The goal was to determine the stability of the radio cores and to assess structure effects associated with positions in the ICRF. Although the four sources were compact at 8.6 GHz, the VLBA images at 43 GHz with 0.3 mas resolution showed that all were composed of several components. A component in each source was identified as the radio core using some or all of the following emission properties: compactness, spectral index, location at the end of the extended emission region, and stationary in the sky. Over the observing period, the relative positions between the four radio cores were constant to 0.02 mas, the phase-referencing positional accuracy obtained at 23 and 43 GHz among the sources, suggesting that once a radio core is identified, it remains stationary in the sky to this accuracy. Other radio components in two of the four sources had detectable motion in the radio jet direction. Comparison of the 23 and 43 GHz VLBA images with the VLBA 8.6 GHz images and the ICRF positions suggests that some ICRF positions are dominated by a moving jet component; hence, they can be displaced up to 0.5 mas from the radio core and may also reflect the motion of the jet component. Future astrometric efforts to determine a more accurate quasar reference frame at 23 and 43 GHz and from the VLBI2010 project are discussed, and supporting VLBA or European VLBI Network observations of ICRF sources at 43 GHz are recommended in order to determine the internal structure of the sources. A future collaboration between the radio (ICRF) and the optical frame of GAIA is discussed.
Forveille, T., Bonfils, X., Lo Curto, G., Delfosse, X., Udry, S., Bouchy, F., Lovis, C., Mayor, M., Moutou, C., Naef, D., Pepe, F., Perrier, C., Queloz, D., Santos, N., 2011, "The HARPS search for southern extra-solar planets. XXVI. Two giant planets around M0 dwarfs," Astronomy and Astrophysics, 526, 141.
Fewer giants planets are found around M dwarfs than around more massive stars, and this dependence of planetary characteristics on the mass of the central star is an important observational diagnostic of planetary formation theories. In part to improve on those statistics, we are monitoring the radial velocities of nearby M dwarfs with the HARPS spectrograph on the ESO 3.6 m telescope. We present here the detection of giant planets around two nearby M0 dwarfs: planets, with minimum masses of respectively 5 Jupiter masses and 1 Saturn mass, orbit around Gl 676A and HIP 12961. The latter is, by over a factor of two, the most massive planet found by radial velocity monitoring of an M dwarf, but its being found around an early M-dwarf is in approximate line with the upper envelope of the planetary vs stellar mass diagram. HIP 12961 ([Fe/H] = -0.07) is slightly more metal-rich than the average solar neighborhood ([Fe/H] = -0.17), and Gl 676A ([Fe/H] = 0.18) significantly so. The two stars together therefore reinforce the growing trend for giant planets being more frequent around more metal-rich M dwarfs, and the 5 Jupiter mass Gl 676Ab being found around a metal-rich star is consistent with the expectation that the most massive planets preferentially form in disks with large condensate masses. Based on observations made with the HARPS instrument on the ESO 3.6-m telescope at La Silla Observatory under program ID 072.C-0488Tables 3 and 4 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/cgi-bin/qcat?J/A+A/526/A141
Foucart, F., Lai, D., 2011, "Evolution of spin direction of accreting magnetic protostars and spin-orbit misalignment in exoplanetary systems - II. Warped discs," Monthly Notices of the Royal Astronomical Society, 234.
Magnetic interactions between a protostar and its accretion disc can induce warping in the disc and produce secular changes in the stellar spin direction, so that the spin axis may not always be perpendicular to the disc. This may help to explain the 7° misalignment between the ecliptic plane of the Solar system and the Sun's equatorial plane as well as play a role in producing the recently observed spin-orbit misalignment in a number of exoplanetary systems. We study the dynamics of warped protoplanetary discs under the combined effects of magnetic warping/precession torques and internal stresses in the disc, including viscous damping of warps and propagation of bending waves. We show that when the outer disc axis is misaligned with the stellar spin axis, the disc evolves towards a warped steady state on a time-scale that depends on the disc viscosity or the bending wave propagation speed, but in all cases is much shorter than the time-scale for the spin evolution (of the order of a million years). Moreover, for the most likely physical parameters characterizing magnetic protostars, circumstellar discs and their interactions, the steady-state disc, averaged over the stellar rotation period, has a rather small warp such that the whole disc lies approximately in a single plane determined by the outer disc boundary conditions, although more extreme parameters may give rise to larger disc warps. In agreement with our recent analysis based on flat discs, we find that the back-reaction magnetic torques of the slightly warped disc on the star can either align the stellar spin axis with the disc axis or push it towards misalignment, depending on the parameters of the star-disc system. This implies that newly formed planetary systems may have a range of inclination angles between the stellar spin axis and the orbital angular momentum axis of the planetary orbits.
Freire, P.C.C., Bassa, C.G., Wex, N., Stairs, I.H., Champion, D.J., Ransom, S.M., Lazarus, P., Kaspi, V.M., Hessels, J.W.T., Kramer, M., Cordes, J.M., Verbiest, J.P.W., Podsiadlowski, P., Nice, D.J., Deneva, J.S., Lorimer, D.R., Stappers, B.W., McLaughlin, M.A., Camilo, F., 2011, "On the nature and evolution of the unique binary pulsar J1903+0327," Monthly Notices of the Royal Astronomical Society, 275.
PSR J1903+0327, a millisecond pulsar in an eccentric (e= 0.44) 95-d orbit with an ∼1 M⊙ companion poses a challenge to our understanding of stellar evolution in binary and multiple-star systems. Here we describe optical and radio observations which rule out most of the scenarios proposed to explain formation of this system. Radio timing measurements of three post-Keplerian effects yield the most precise measurement of the mass of a millisecond pulsar to date: 1.667 ± 0.021 solar masses (99.7 per cent confidence limit). This rules out some equations of state for superdense matter; furthermore, it is consistent with the spin-up of the pulsar by mass accretion, as suggested by its short spin period and low magnetic field. Optical spectroscopy of a proposed main-sequence counterpart shows that its orbital motion mirrors the pulsar.s 95-d orbit; being therefore its binary companion. This finding rules out a previously suggested scenario which proposes that the system is presently a hierarchical triple. Conventional binary evolution scenarios predict that, after recycling a neutron star into a millisecond pulsar, the binary companion should become a white dwarf and its orbit should be nearly circular. This suggests that if PSR J1903+0327 was recycled, its present companion was not responsible for it. The optical detection also provides a measurement of the systemic radial velocity of the binary; this and the proper motion measured from pulsar timing allow the determination of the systemic 3D velocity in the Galaxy. We find that the system is always within 270 pc of the plane of the Galaxy, but always more than 3 kpc away from the Galactic Centre. Thus an exchange interaction in a dense stellar environment (like a globular cluster or the Galactic Centre) is not likely to be the origin of this system. We suggest that after the supernova that formed it, the neutron star was in a tight orbit with a main-sequence star and the present companion was a tertiary farther out. The neutron star then accreted matter from its evolving inner companion, forming a millisecond pulsar. The inner companion then disappeared, either due to a chaotic three-body interaction with the outer star (caused by the expansion of the inner orbit that necessarily results from mass transfer), or in the case of a very compact inner system, due to ablation/accretion by the newly formed millisecond pulsar. We discuss in detail the possible evolution of such a system before the supernova.
Funk, B., Libert, A.-S., Sü., Pilat-Lohinger, E., 2011, "On the influence of the Kozai mechanism in habitable zones of extrasolar planetary systems," Astronomy and Astrophysics, 526, 98.
Aims: We investigate the long-term evolution of inclined test particles representing a small Earth-like body with negligible gravitational effects (hereafter called massless test-planets) in the restricted three-body problem, and consisting of a star, a gas giant, and a massless test-planet. The test-planet is initially on a circular orbit and moves around the star at distances closer than the gas giant. The aim is to show the influences of the eccentricity and the mass of the gas giant on the dynamics, for various inclinations of the test-planet, and to investigate in more detail the Kozai mechanism in the elliptic problem.
Methods: We performed a parametric study, integrating the orbital evolution of test particles whose initial conditions were distributed on the semi-major axis - inclination plane. The gas giant's initial eccentricity was varied. For the calculations, we used the Lie integration method and in some cases the Bulirsch-Stoer algorithm. To analyze the results, the maximum eccentricity and the Lyapunov characteristic indicator were used. All integrations were performed for 105 periods of the gas giant.
Results: Our calculations show that inclined massless test-planets can be in stable configurations with gas giants on either circular or elliptic orbits. The higher the eccentricity of the gas giant, the smaller the possible range in semi-major axis for the test-planet. For gas giants on circular orbits, our results illustrate the well-known results associated with the Kozai mechanism, which do not allow stable orbits above a critical inclination of approximately 40°. For gas giants on eccentric orbits, the dynamics is quite similar, and the massless companion exhibits limited variations in eccentricity. In addition, we identify a region around 35° consisting of long-time stable, low eccentric orbits. We show that these results are also valid for Earth-mass companions, therefore they can be applied to extrasolar systems: for instance, the extrasolar planetary system HD 154345 can possess a 35° degree inclined, nearly circular, Earth-mass companion in the habitable zone.
Gardner, E., Nurmi, P., Flynn, C., Mikkola, S., 2011, "The effect of the solar motion on the flux of long-period comets," Monthly Notices of the Royal Astronomical Society, 411, 947-954.
The long-term dynamics of Oort cloud comets are studied under the influence of both the radial and the vertical components of the Galactic tidal field. Sporadic dynamical perturbation processes, such as passing stars, are ignored since we aim to study the influence of just the axisymmetric Galactic tidal field on the cometary motion and how it changes in time. We use a model of the Galaxy with a disc, bulge and dark halo, and a local disc density and disc scalelength constrained to fit the best available observational constraints. By integrating a few million of cometary orbits over 1 Gyr, we calculate the time variable flux of Oort cloud comets that enter the inner Solar system for the cases of a constant Galactic tidal field and a realistically varying tidal field, which is a function of the Sun's orbit. The applied method calculates the evolution of the comets by using first-order averaged mean elements. We find that the periodicity in the cometary flux is complicated and quasi-periodic. The amplitude of the variations in the flux is of the order of 30 per cent. The radial motion of the Sun is the chief cause of this behaviour, and should be taken into account when the Galactic influence on the Oort cloud comets is studied.
Genov, D.A., 2011, "General relativity: Optical black-hole analogues," Nature Photonics, 5, 76-78.
Optical analogues of gravity let scientists interrogate astronomical phenomena that are otherwise difficult or impossible to study.
Haller, G., Uzer, T., Palaciá J., Yanguas, P., JafféC., 2011, "Transition state geometry near higher-rank saddles in phase space," Nonlinearity, 24, 527-561.
We present a detailed analysis of invariant phase space structures near higher-rank saddles of Hamiltonian systems. Using the theory of pseudo-hyperbolic invariant surfaces, we show the existence of codimension-one normally hyperbolic invariant manifolds that govern transport near the higher-rank saddle points. Such saddles occur in a number of problems in celestial mechanics, chemical reactions, and atomic physics. As an example, we consider the problem of double ionization of helium in an external electric field, a basis of many modern ionization experiments. In this example, we illustrate our main results on the geometry and transport properties near a rank-two saddle.
Hannam, M., Hawke, I., 2011, "Numerical relativity simulations in the era of the Einstein Telescope," General Relativity and Gravitation, 43, 465-483.
Numerical-relativity (NR) simulations of compact binaries are expected to be an invaluable tool in gravitational-wave astronomy. The sensitivity of future detectors such as the Einstein Telescope (ET) will place much higher demands on NR simulations than first- and second-generation ground-based detectors. We discuss the issues facing compact-object simulations over the next decade, with an emphasis on estimating where the accuracy and parameter space coverage will be sufficient for ET and where significant work is needed.
Haranas, I., Ragos, O., Mioc, V., 2011, "Yukawa-type potential effects in the anomalistic period of celestial bodies," Astrophysics and Space Science, 332, 107-113.
Several contemporary modified models of gravity predict the existence of a non-Newtonian Yukawa-type correction to the classical gravitational potential. We study the motion of a secondary celestial body under the influence of the corrected gravitational force of a primary. We derive two equations to approximate the periastron time rate of change and its total variation over one revolution (i.e., the difference between the anomalistic period and the Keplerian period) under the influence of the non-Newtonian radial acceleration. Kinematically, this influence produces apsidal motion. We performed numerical estimations for Mercury, for the companion star of the pulsar PSR 1913+16, and for the extrasolar Planet b of the star HD 80606. We also considered the case of the artificial Earth satellite GRACE-A, but the results present a low degree of reliability from a practical standpoint.
Harris, A.W., Mommert, M., Hora, J.L., Mueller, M., Trilling, D.E., Bhattacharya, B., Bottke, W.F., Chesley, S., Delbo, M., Emery, J.P., Fazio, G., Mainzer, A., Penprase, B., Smith, H.A., Spahr, T.B., Stansberry, J.A., Thomas, C.A., 2011, "ExploreNEOs. II. The Accuracy of the Warm Spitzer Near-Earth Object Survey," The Astronomical Journal, 141, 75.
We report on results of observations of near-Earth objects (NEOs) performed with the NASA Spitzer Space Telescope as part of our ongoing (2009-2011) Warm Spitzer NEO survey ("ExploreNEOs"), the primary aim of which is to provide sizes and albedos of some 700 NEOs. The emphasis of the work described here is an assessment of the overall accuracy of our survey results, which are based on a semi-empirical generalized model of asteroid thermal emission. The NASA Spitzer Space Telescope has been operated in the so-called Warm Spitzer mission phase since the cryogen was depleted in 2009 May, with the two shortest-wavelength channels, centered at 3.6 ?m and 4.5 ?m, of the Infrared Array Camera continuing to provide valuable data. The set of some 170 NEOs in our current Warm Spitzer results catalog contains 28 for which published taxonomic classifications are available, and 14 for which relatively reliable published diameters and albedos are available. A comparison of the Warm Spitzer results with previously published results ("ground truth"), complemented by a Monte Carlo error analysis, indicates that the rms Warm Spitzer diameter and albedo errors are ±20% and ±50%, respectively. Cases in which agreement with results from the literature is worse than expected are highlighted and discussed; these include the potential spacecraft target 138911 2001 AE2. We confirm that 1.4 appears to be an appropriate overall default value for the relative reflectance between the V band and the Warm Spitzer wavelengths, for use in correction of the Warm Spitzer fluxes for reflected solar radiation.
Hartman, J.D., Bakos, G.Á, Kipping, D.M., Torres, G., Ková, G., Noyes, R.W., Latham, D.W., Howard, A.W., Fischer, D.A., Johnson, J.A., Marcy, G.W., Isaacson, H., Quinn, S.N., Buchhave, L.A., Bé, B., Sasselov, D.D., Stefanik, R.P., Esquerdo, G.A., Everett, M., Perumpilly, G., Lár, J., Papp, I., Sá, P., 2011, "HAT-P-26b: A Low-density Neptune-mass Planet Transiting a K Star," The Astrophysical Journal, 728, 138.
We report the discovery of HAT-P-26b, a transiting extrasolar planet orbiting the moderately bright V = 11.744 K1 dwarf star GSC 0320-01027, with a period P = 4.234516 ± 0.000015 days, transit epoch Tc = 2455304.65122 ± 0.00035 (BJD; Barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time (UTC)), and transit duration 0.1023 ± 0.0010 days. The host star has a mass of 0.82 ± 0.03 M sun, radius of 0.79+0.10 -0.04 R sun, effective temperature 5079 ± 88 K, and metallicity [Fe/H] = -0.04 ± 0.08. The planetary companion has a mass of 0.059 ± 0.007 M J, and radius of 0.565+0.072 -0.032 R J yielding a mean density of 0.40 ± 0.10 g cm-3. HAT-P-26b is the fourth Neptune-mass transiting planet discovered to date. It has a mass that is comparable to those of Neptune and Uranus, and slightly smaller than those of the other transiting Super-Neptunes, but a radius that is ~65% larger than those of Neptune and Uranus, and also larger than those of the other transiting Super-Neptunes. HAT-P-26b is consistent with theoretical models of an irradiated Neptune-mass planet with a 10 M ⊕ heavy element core that comprises gsim50% of its mass with the remainder contained in a significant hydrogen-helium envelope, though the exact composition is uncertain as there are significant differences between various theoretical models at the Neptune-mass regime. The equatorial declination of the star makes it easily accessible to both Northern and Southern ground-based facilities for follow-up observations.
Hartung, J., Steinhoff, J., 2011, "Next-to-leading order spin-orbit and spin(a)-spin(b) Hamiltonians for n gravitating spinning compact objects," Physical Review D, 83, 44008.
We derive the post-Newtonian next-to-leading order conservative spin-orbit and spin(a)-spin(b) gravitational interaction Hamiltonians for arbitrary many compact objects. The spin-orbit Hamiltonian completes the knowledge of Hamiltonians up to and including 2.5 post Newtonian for the general relativistic three-body problem. The new Hamiltonians include highly nontrivial three-body interactions, in contrast to the leading order consisting of two-body interactions only. This may be important for the study of effects like Kozai resonances in mergers of black holes with binary black holes. The derivation was done via two independent methods giving fully consistent results.
Hashimoto, J., Tamura, M., Muto, T., Kudo, T., Fukagawa, M., Fukue, T., Goto, M., Grady, C.A., Henning, T., Hodapp, K., Honda, M., Inutsuka, S., Kokubo, E., Knapp, G., McElwain, M.W., Momose, M., Ohashi, N., Okamoto, Y.K., Takami, M., Turner, E.L., Wisniewski, J., Janson, M., Abe, L., Brandner, W., Carson, J., Egner, S., Feldt, M., Golota, T., Guyon, O., Hayano, Y., Hayashi, M., Hayashi, S., Ishii, M., Kandori, R., Kusakabe, N., Matsuo, T., Mayama, S., Miyama, S., Morino, J.-I., Moro-Martin, A., Nishimura, T., Pyo, T.-S., Suto, H., Suzuki, R., Takato, N., Terada, H., Thalmann, C., Tomono, D., Watanabe, M., Yamada, T., Takami, H., Usuda, T., 2011, "Direct Imaging of Fine Structures in Giant Planet-forming Regions of the Protoplanetary Disk Around AB Aurigae," The Astrophysical Journal, 729, L17.
We report high-resolution 1.6 μm polarized intensity (PI) images of the circumstellar disk around the Herbig Ae star AB Aur at a radial distance of 22 AU (015) up to 554 AU (385), which have been obtained by the high-contrast instrument HiCIAO with the dual-beam polarimetry. We revealed complicated and asymmetrical structures in the inner part (140 AU) of the disk while confirming the previously reported outer (r 200 AU) spiral structure. We have imaged a double ring structure at ~40 and ~100 AU and a ring-like gap between the two. We found a significant discrepancy of inclination angles between two rings, which may indicate that the disk of AB Aur is warped. Furthermore, we found seven dips (the typical size is ~45 AU or less) within two rings, as well as three prominent PI peaks at ~40 AU. The observed structures, including a bumpy double ring, a ring-like gap, and a warped disk in the innermost regions, provide essential information for understanding the formation mechanism of recently detected wide-orbit (r > 20 AU) planets.
Haskell, B., 2011, "Tkachenko modes in rotating neutron stars: The effect of compressibility and implications for pulsar timing noise," Physical Review D, 83, 43006.
Long wavelength oscillations (Tkachenko waves) of the triangular lattice of quantized vortices in superfluid neutron stars have been suggested as one of the possible explanations for the timing noise observed in many radio pulsars, in particular, for the 100-1000 day variations in the spin of PSR 1828-11. Most studies to date have, however, been based on the hydrodynamics developed for superfluid Helium. In this paper we extend the formulation to a two-fluid neutron and proton system, relevant for neutron star interiors and include the effect of chemical coupling, compressibility and mutual friction between the components. In particular we find that chemical coupling and compressibility can have a drastic effect on the mode structure. However, for the slower pulsars rotating at 1-10 Hz (such as PSR B1828-11), most choices of parameters in the equation of state lead to Tkachenko oscillations with frequencies in the correct range to explain the timing noise. We also investigate the case of more rapidly rotating pulsars (above 100 Hz) for which we find that there is a vast portion of parameter space in which there are no Tkachenko modes, but only modified sound waves at much higher frequencies.
Héard, G., Ehrenreich, D., Bouchy, F., Delfosse, X., Moutou, C., Arnold, L., Boisse, I., Bonfils, X., Dí, R.F., Eggenberger, A., Forveille, T., Lagrange, A.-M., Lovis, C., Pepe, F., Perrier, C., Queloz, D., Santerne, A., Santos, N.C., Séansan, D., Udry, S., Vidal-Madjar, A., 2011, "The retrograde orbit of the HAT-P-6b exoplanet," Astronomy and Astrophysics, 527, L11.
We observed the transit of the HAT-P-6b exoplanet across its host star with the SOPHIE spectrograph (OHP, France). The resulting stellar radial velocities display the Rossiter-McLaughlin anomaly and reveal a retrograde orbit: the planetary orbital spin and the stellar rotational spin point in approximately opposite directions. A fit to the anomaly measures a sky-projected angle λ = 166° ± 10° between these two spin axes. All seven known retrograde planets are hot Jupiters with masses Mp < 3 MJup. About two thirds of the planets in this mass range, however, are prograde and aligned (λ ≃ 0°). In contrast, most of the more massive planets (Mp > 4 MJup) are prograde but misaligned. Different mechanisms may therefore be responsible for planetary obliquities above and below ~3.5 MJup.
Howard, A.W., Johnson, J.A., Marcy, G.W., Fischer, D.A., Wright, J.T., Henry, G.W., Isaacson, H., Valenti, J.A., Anderson, J., Piskunov, N.E., 2011, "The NASA-UC Eta-Earth Program. III. A Super-Earth Orbiting HD 97658 and a Neptune-mass Planet Orbiting Gl 785," The Astrophysical Journal, 730, 10.
We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and Gl 785. These planets were detected by Keplerian modeling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass Msin i = 8.2 ± 1.2 M ⊕, orbital period P = 9.494 ± 0.005 days, and an orbit that is consistent with circular. Gl 785 b is a Neptune-mass planet with Msin i = 21.6 ± 2.0 M ⊕, P = 74.39 ± 0.12 days, and orbital eccentricity e = 0.30 ± 0.09. Photometric observations with the T12 0.8 m automatic photometric telescope at Fairborn Observatory show that HD 97658 is photometrically constant at the radial velocity period to 0.09 mmag, supporting the existence of the planet.
Huerta, E.A., Gair, J.R., 2011, "Intermediate-mass-ratio inspirals in the Einstein Telescope. I. Signal-to-noise ratio calculations," Physical Review D, 83, 44020.
Einstein Telescope (ET) is a proposed third-generation ground-based interferometric gravitational wave detector, for which the target is a sensitivity that is a factor of 10 better than Advanced LIGO and a frequency range that extends down to∼1 Hz. Such a third-generation interferometer will provide opportunities to test Einstein.s theory of relativity in the strong field and will realize precision gravitational wave astronomy with a thousandfold increase in the expected number of events over the advanced ground-based detectors. A design study for ET is currently underway, so it is timely to assess the science that could be done with such an instrument. This paper is the first in a series that will carry out a detailed study of intermediate-mass-ratio inspirals (IMRIs) for ET. In the context of ET, an IMRI is the inspiral of a neutron star or stellar-mass black hole into an intermediate mass black hole (IMBH). In this paper we focus on the development of IMRI waveform models for circular and equatorial inspirals. We consider two approximations for the waveforms, which both incorporate the inspiral, merger, and ringdown phases in a consistent way. One approximation, valid for IMBHs of arbitrary spin, uses the transition model of Ori and Thorne [A. Ori and K. S. Thorne, Phys. Rev. D 62, 124022 (2000).] to describe the merger, and this is then matched smoothly onto a ringdown waveform. The second approximation uses the effective one body approach to model the merger phase of the waveform and is valid for nonspinning IMBHs. In this paper, we use both waveform models to compute signal-to-noise ratios for IMRI sources detectable by ET. At a redshift of z=1, we find typical signal-to-noise ratios for IMRI systems
with masses 1.4M⊙+100M⊙, 10M⊙+100M⊙, 1.4M⊙+500M⊙ and 10M⊙+500M⊙ of ∼10.25, ∼40.80,∼3.15, and ∼10.60, respectively. We also find that the two models make predictions for nonspinning inspirals that are consistent to about 10%.
Ibgui, L., Spiegel, D.S., Burrows, A., 2011, "Explorations into the Viability of Coupled Radius-orbit Evolutionary Models for Inflated Planets," The Astrophysical Journal, 727, 75.
The radii of some transiting extrasolar giant planets are larger than would be expected by the standard theory. We address this puzzle with the model of coupled radius-orbit tidal evolution developed by Ibgui & Burrows. The planetary radius is evolved self-consistently with orbital parameters, under the influence of tidal torques and tidal dissipation in the interior of the planet. A general feature of this model, which we have previously demonstrated in the generic case, is that a possible transient inflation of the planetary radius can temporarily interrupt its standard monotonic shrinking and can lead to the inflated radii that we observe. Importantly, we demonstrate that the use of a constant time lag model for the orbital evolution does not improve the accuracy of the evolutionary calculations. First, though formulated in a closed form by the equations of Hut, it is not valid at large eccentricities, as for the constant phase lag model truncated at the second order in eccentricity that we adopt; ambiguities in tidal theories are perhaps the most significant source of uncertainty in evolutionary calculations. Second, we find evolutionary tracks that fit within the 1σ error bars, the radius, the eccentricity, and the semimajor axis of HD 209458b in its current estimated age range, using the constant time lag model, as we find fitting tracks with the constant phase lag model. Both models show that a bloated planet with a circular orbit may still be inflated, due to thermal inertia. We have modified our constant phase lag model to include an orbital period dependence of the tidal dissipation factor in the star, Q'* P γ, .1 ≤ γ ≤ 1. For some inflated planets (WASP-6b and WASP-15b), we find fitting tracks; for another (TrES-4), we do not; and for others (WASP-4b and WASP-12b), we find fitting tracks, but our model might imply that we are observing the planets at a special time. Finally, we stress a 2-3 order-of-magnitude timescale uncertainty of the inspiraling phase of the planet into its host star, arising from uncertainties in Q'*.
Iorio, L., 2011, "Classical and relativistic long-term time variations of some observables for transiting exoplanets," Monthly Notices of the Royal Astronomical Society, 411, 167-183.
We analytically work out the long-term, i.e. averaged over one orbital revolution, time variations of some direct observable quantities Y induced by classical and general relativistic dynamical perturbations of the two-body point-like Newtonian acceleration in the case of transiting exoplanets moving along elliptic orbits. More specifically, the observables Y with which we deal are the transit duration Δtd, the radial velocity Vρ, the time interval Δtecl between primary and secondary eclipses, and the time interval Ptr between successive primary transits. The dynamical effects considered are the centrifugal oblateness of both the star and the planet, their tidal bulges mutually raised on each other, a distant third-body X and general relativity (both Schwarzschild and Lense.Thirring). We take into account the effects due to the perturbations of all the Keplerian orbital elements involved in a consistent and uniform way. First, we explicitly compute their instantaneous time variations due to the dynamical effects considered and substitute them in the general expression for the instantaneous change of Y; then, we take the overall average over one orbital revolution of the so-obtained instantaneous rate specialized to the perturbations considered. In contrast, previous published works have often employed somewhat .hybrid. expressions, in which the secular precession of, typically, the periastron only is straightforwardly inserted into instantaneous formulas. The transit duration is affected neither by the general relativistic Schwarzschild-type nor by the classical tidal effects, while the bodies. centrifugal oblatenesses, a distant third-body X and the general relativistic Lense.Thirring-type perturbations induce non-vanishing long-term, harmonic effects on Δtd also for circular orbits. For exact edge-on configurations they vanish. Both Vρ and Δtecl experience non-vanishing long-term, harmonic variations, caused by all the perturbations considered, only for non-circular orbits. Also Ptr is affected by all of them with long-term signatures, but they do not vanish for circular orbits. Numerical evaluations of the obtained results are given for a typical star.planet scenario and compared with the expected observational accuracies over a time-span τ= 10 yr long. Also graphical investigations of the dependence of the effects considered on the semimajor axis and the eccentricity are presented. Our results are, in principle, valid also for other astronomical scenarios. They may allow, e.g., for designing various tests of gravitational theories with natural and artificial bodies in our Solar system.
Iorio, L., 2011, "Classical and relativistic node precessional effects in WASP-33b and perspectives for detecting them," Astrophysics and Space Science, 331, 485-496.
WASP-33 is a fast rotating, main sequence star which hosts a hot Jupiter moving along a retrograde and almost polar orbit with semi-major axis a=0.02 au and eccentricity provisionally set to e=0. The quadrupole mass moment J2 and the proper angular momentum S ⋆ of the star are 1900 and 400 times, respectively, larger than those of the Sun. Thus, huge classical and general relativistic non-Keplerian orbital effects should take place in such a system. In particular, the large inclination Ψ⋆ of the orbit of WASP-33b to the star.s equator allows to consider the node precession and the related time variation dt d /dt of the transit duration t d . The WASP-33b node rate due to J2 is 9×09 times larger than the same effect for Mercury induced by the Sun.s oblateness, while the general relativistic gravitomagnetic node precession is 3×05 times larger than the Lense-Thirring effect for Mercury due to the Sun.s rotation. We also consider the effect of the centrifugal oblateness of the planet itself and of a putative distant third body X. The magnitudes of the induced time change in the transit duration are of the order of 3×0−6,2×0−7,8×0−9 for J2 , the planet.s rotational oblateness and general relativity, respectively. A yet undiscovered planet X with the mass of Jupiter orbiting at more than 1 au would induce a transit duration variation of less than 4×0−9. A conservative evaluation of the accuracy in measuring dt d /dt over 10 yr points towards ≈10−8. The analysis presented here will be applicable also to other exoplanets with similar features if and when they will ne discovered.
Iorio, L., Lichtenegger, H.I.M., Ruggiero, M.L., Corda, C., 2011, "Phenomenology of the Lense-Thirring effect in the solar system," Astrophysics and Space Science, 331, 351-395.
Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate the present and future perspectives in directly measuring such an elusive relativistic effect.
Jin, S., Zhang, L.J., Tapley, B.D., 2011, "The understanding of length-of-day variations from satellite gravity and laser ranging measurements," Geophysical Journal International, 184, 651-660.
The change in the rate of the Earth's rotation, length-of-day (LOD), is principally the result of movement and redistribution of mass in the Earth's atmosphere, oceans and hydrosphere. Numerous studies on the LOD excitations have been made from climatological/hydrological assimilation systems and models of the general circulation of the ocean. However, quantitative assessment and understanding of the contributions to the LOD remain unclear due mainly to the lack of direct global observations. In this paper, the total Earth's surface fluids mass excitations to the LOD at seasonal and intraseasonal timescales are investigated from the Jet Propulsion Laboratory Estimating Circulation and Climate of the Ocean (ECCO) model, the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and the European Center for Medium-Range Weather Forecasts (ECMWF) Re-analysis (ERA)-Interim, GRACE-derived surface fluids mass and the spherical harmonics coefficient C20 from the satellite laser ranging (SLR) as well as combined GRACE+SLR solutions, respectively. Results show that the GRACE and the combined GRACE and SLR solutions better explain the geodetic residual LOD excitations at annual and semi-annual timescales. For less than 1 yr timescales, GRACE-derived mass is worse to explain the geodetic residuals, whereas SLR agrees better with the geodetic residuals. However, the combined GRACE and SLR results are much improved in explaining the geodetic residual excitations at intraseasonal scales.
Jones, D.L., Fomalont, E., Dhawan, V., Romney, J., Folkner, W.M., Lanyi, G., Border, J., Jacobson, R.A., 2011, "Very Long Baseline Array Astrometric Observations of the Cassini Spacecraft at Saturn," The Astronomical Journal, 141, 29.
The planetary ephemeris is an essential tool for interplanetary spacecraft navigation, studies of solar system dynamics (including, for example, barycenter corrections for pulsar timing ephemerides), the prediction of occultations, and tests of general relativity. We are carrying out a series of astrometric very long baseline interferometry observations of the Cassini spacecraft currently in orbit around Saturn, using the Very Long Baseline Array (VLBA). These observations provide positions for the center of mass of Saturn in the International Celestial Reference Frame (ICRF) with accuracies ~0.3 mas (1.5 nrad) or about 2 km at the average distance of Saturn. This paper reports results from eight observing epochs between 2006 October and 2009 April. These data are combined with two VLBA observations by other investigators in 2004 and a Cassini-based gravitational deflection measurement by Fomalont et al. in 2009 to constrain a new ephemeris (DE 422). The DE 422 post-fit residuals for Saturn with respect to the VLBA data are generally 0.2 mas, but additional observations are needed to improve the positions of all of our phase reference sources to this level. Over time we expect to be able to improve the accuracy of all three coordinates in the Saturn ephemeris (latitude, longitude, and range) by a factor of at least three. This will represent a significant improvement not just in the Saturn ephemeris but also in the link between the inner and outer solar system ephemerides and in the link to the inertial ICRF.
Jones, D.L., Fomalont, E., Dhawan, V., Romney, J., Folkner, W.M., Lanyi, G., Border, J., Jacobson, R.A., Kimura, T., Tsuchiya, F., Misawa, H., Morioka, A., Nishimura, Y., 2011, "Very Long Baseline Array Astrometric Observations of the Cassini Spacecraft at Saturn," The Astronomical Journal, 141, 29.
The planetary ephemeris is an essential tool for interplanetary spacecraft navigation, studies of solar system dynamics (including, for example, barycenter corrections for pulsar timing ephemerides), the prediction of occultations, and tests of general relativity. We are carrying out a series of astrometric very long baseline interferometry observations of the Cassini spacecraft currently in orbit around Saturn, using the Very Long Baseline Array (VLBA). These observations provide positions for the center of mass of Saturn in the International Celestial Reference Frame (ICRF) with accuracies ~0.3 mas (1.5 nrad) or about 2 km at the average distance of Saturn. This paper reports results from eight observing epochs between 2006 October and 2009 April. These data are combined with two VLBA observations by other investigators in 2004 and a Cassini-based gravitational deflection measurement by Fomalont et al. in 2009 to constrain a new ephemeris (DE 422). The DE 422 post-fit residuals for Saturn with respect to the VLBA data are generally 0.2 mas, but additional observations are needed to improve the positions of all of our phase reference sources to this level. Over time we expect to be able to improve the accuracy of all three coordinates in the Saturn ephemeris (latitude, longitude, and range) by a factor of at least three. This will represent a significant improvement not just in the Saturn ephemeris but also in the link between the inner and outer solar system ephemerides and in the link to the inertial ICRF.
Kennedy, G.M., Wyatt, M.C., 2011, "Collisional evolution of irregular satellite swarms: detectable dust around Solar system and extrasolar planets," Monthly Notices of the Royal Astronomical Society, 135.
Since the 1980s it has been becoming increasingly clear that the Solar system.s irregular satellites are collisionally evolved. The current populations are remnants of much more massive swarms that have been grinding away for billions of years. Here, we derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar system and extrasolar planets. The model uses a particle-in-a-box formalism and considers implications for the size distribution, which allows a connection between irregular satellite populations and predicted levels in the resulting dust cloud. Our model reproduces the Solar system.s complement of observed irregulars well, and suggests that the competition between grain.grain collisions and Poynting.Robertson (PR) drag helps set the fate of the dust. In collision-dominated swarms most dust is lost to interplanetary space or impacts the host planet, while PR-dominated grains spiral in towards the planet through the domain of regular satellites. Because swarm collision rates decrease over time the main dust sink can change with time, and may help unravel the accretion history of synchronously rotating regular satellites that show brightness asymmetries, such as Callisto and Iapetus. Some level of dust must be present on au scales around the Solar system.s giant planets if the irregular satellites are still grinding down, which we predict may be at detectable levels. We also use our model to predict whether dust produced by extrasolar circumplanetary swarms can be detected. Though designed with planets in mind, the coronagraphic instruments on James Webb Space Telescope (JWST) will have the ability to detect the dust generated by these swarms, which are most detectable around planets that orbit at many tens of au from the youngest stars. Because the collisional decay of swarms is relatively insensitive to planet mass, swarms can be much brighter than their host planets and allow discovery of Neptune-mass planets that would otherwise remain invisible. This dust could have been detected by Hubble Space Telescope Advanced Camera for Surveys (HST ACS) coronagraphic observations, and in one case dust may have already been detected. The observations of the planet Fomalhaut b can be explained as scattered light from dust produced by the collisional decay of an irregular satellite swarm around a ∼10 M⊕ planet. Such a swarm comprises about 5 lunar masses worth of irregular satellites. Finally, we briefly consider what happens if Fomalhaut b passes through Fomalhaut.s main debris ring on a coplanar orbit, which allows the circumplanetary swarm to be replenished through collisions with ring planetesimals. This scenario, in which the planet is at least of the order of an Earth mass, may be ruled out by the narrow structure of the debris ring.
Kholshevnikov, K.V., Kuznetsov, E.D., 2011, "Stability of planetary systems with respect to masses," Celestial Mechanics and Dynamical Astronomy, 109, 201-210.
The stability in the sense of Lagrange of the Sun-Jupiter-Saturn system and 47 UMa system with respect to masses on a time scale of 10<SUP>6</SUP> years was studied using the method of averaging and numerical methods. When the masses of Jupiter and Saturn increase by 20 times (approximately, more accurate value depends on a time-scale of stable motion), these planets can have close approaches. Close approaches appear when analyzing osculating elements; they are absent in the mean elements. A similar situation takes place in the case of 47 UMa and other exoplanetary systems. The study of Lagrange stability with respect to masses allows us to obtain upper limits for masses of extrasolar planets.
Kipping, D., Bakos, G., 2011, "An Independent Analysis of Kepler-4b Through Kepler-8b," The Astrophysical Journal, 730, 50.
We present two independent, homogeneous, global analyses of the transit light curves, radial velocities, and spectroscopy of Kepler-4b, Kepler-5b, Kepler-6b, Kepler-7b, and Kepler-8b with numerous differences compared to the previous methods. These include: (1) improved decorrelated parameter fitting set used, (2) new limb-darkening coefficients, (3) time stamps modified to barycentric Julian date for consistency with radial velocity data, (4) two different methods for compensating for the long integration time of Kepler long-cadence data, (5) best-fit secondary eclipse depths and excluded upper limits, and (6) fitted mid-transit times, durations, depths, and baseline fluxes for individual transits. We make several determinations not found in the discovery papers. (1) We detect a secondary eclipse for Kepler-7b of depth (47 ± 14) ppm and statistical significance 3.5σ. We conclude that reflected light is a much more plausible origin than thermal emission and determine a geometric albedo of Ag = (0.38 ± 0.12). (2) We find that an eccentric orbit model for the Neptune-mass planet Kepler-4b is detected at the 2σ level with e = (0.25 ± 0.12). If confirmed, this would place Kepler-4b in a similar category as GJ 436b and HAT-P-11b, as an eccentric, Neptune-mass planet. (3) We find weak evidence for a secondary eclipse in Kepler-5b of 2σ significance and depth (26 ± 17) ppm. The most plausible explanation is reflected light caused by a planet of geometric albedo Ag = (0.15 ± 0.10). (4) A 2.6σ peak in Kepler-6b TTV periodogram is detected and is not easily explained as an aliased frequency. We find that mean-motion resonant (MMR) perturbers, non-resonant perturbers, and a companion extrasolar moon all provide inadequate explanations for this signal and the most likely source is stellar rotation. (5) We find different impact parameters relative to the discovery papers in most cases, but generally self-consistent when compared to the two methods employed here. (6) We constrain the presence of MMR planets for all five planets through an analysis of the mid-transit times. (7) We constrain the presence of extrasolar moons for all five planets. (8) We constrain the presence of Trojans for all five planets.
Kocsis, B., Sesana, A., 2011, "Gas-driven massive black hole binaries: signatures in the nHz gravitational wave background," Monthly Notices of the Royal Astronomical Society, 411, 1467-1479.
Pulsar timing arrays (PTAs) measure nHz frequency gravitational waves (GWs) generated by orbiting massive black hole binaries (MBHBs) with periods between 0.1 and 10 yr. Previous studies on the nHz GW background assumed that the inspiral is purely driven by GWs. However, torques generated by a gaseous disc can shrink the binary much more efficiently than GW emission, reducing the number of binaries at these separations. We use simple disc models for the circumbinary gas and for the binary.disc interaction to follow the orbital decay of MBHBs through physically distinct regions of the disc, until GWs take over their evolution. We extract MBHB cosmological merger rates from the Millennium simulation, generate Monte Carlo realizations of a population of gas-driven binaries and calculate the corresponding GW amplitudes of the most luminous individual binaries and the stochastic GW background. For steady state -discs with > 0.1, we find that the nHz GW background can be significantly modified. The number of resolvable binaries is however not changed by the presence of gas; we predict 1.10 individually resolvable sources to stand above the noise for a 1.50 ns timing precision. Gas-driven migration reduces predominantly the number of small total mass or unequal mass ratio binaries, which leads to the attenuation of the mean stochastic GW background, but increases the detection significance of individually resolvable binaries. The results are sensitive to the model of binary.disc interaction. The GW background is not attenuated significantly for time-dependent models of Ivanov, Papaloizou & Polnarev.
Korobkin, O., Abdikamalov, E.B., Schnetter, E., Stergioulas, N., Zink, B., 2011, "Stability of general-relativistic accretion disks," Physical Review D, 83, 43007.
Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a Γ-law equation of state with Γ=4/3. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.
Kushvah, B.S., 2011, "Trajectory and stability of Lagrangian point L 2 in the Sun-Earth system," Astrophysics and Space Science, 332, 99-106.
This paper describes design of the trajectory and analysis of the stability of collinear point L2 in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are considered. The point L2 is asymptotically stable up to a specific value of time t correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable to locate a satellite, a telescope or a space station around the point L2.
Lafreniè, D., Jayawardhana, R., Janson, M., Helling, C., Witte, S., Hauschildt, P., 2011, "Discovery of an ~23 M Jup Brown Dwarf Orbiting ~700 AU from the Massive Star HIP 78530 in Upper Scorpius," The Astrophysical Journal, 730, 42.
We present the discovery of a substellar companion on a wide orbit around the ~ 2.5 Mstar HIP 78530, which is a member of the 5 Myr old Upper Scorpius association. We have obtained follow-up imaging over two years and show that the companion and primary share common proper motion. We have also obtained JHK spectroscopy of the companion and confirm its low surface gravity, in accordance with the young age of the system. A comparison with DRIFT-PHOENIX synthetic spectra indicates an effective temperature of 2800 ± 200 K and a comparison with template spectra of young and old dwarfs indicates a spectral type of M8 ± 1. The mass of the companion is estimated to be 19-26 M Jup based on its bolometric luminosity and the predictions of evolutionary models. The angular separation of the companion is 45, which at the distance of the primary star, 156.7 pc, corresponds to a projected separation of ~710 AU. This companion features one of the lowest mass ratios (~0.009) of any known companion at separations greater than 100 AU.
Lantoine, G., Russell, R.P., 2011, "Complete closed-form solutions of the Stark problem," Celestial Mechanics and Dynamical Astronomy, 6.
Perturbed two-body problems play a special role in Celestial Mechanics as they capture the dominant dynamics for a broad range of natural and artificial satellites. In this paper, we investigate the classic Stark problem, corresponding to motion in a Newtonian gravitational field subjected to an additional uniform force of constant magnitude and direction. For both the two-dimensional and three-dimensional cases, the integrals of motion are determined, and the resulting quadratures are analytically integrated. A complete list of exact, closed-form solutions is deduced in terms of elliptic functions. It is found that all expressions rely on only seven fundamental solution forms. Particular attention is given to ensure that the expressions are well-behaved for very small perturbations. A comprehensive study of the phase space is also made using a boundary diagram to describe the domains of the general types of possible motion. Numerical examples are presented to validate the solutions.
Laughlin, G., Crismani, M., Adams, F.C., 2011, "On the Anomalous Radii of the Transiting Extrasolar Planets," The Astrophysical Journal, 729, L7.
We present a systematic evaluation of the agreement between the observed radii of 90 well-characterized transiting extrasolar giant planets and their corresponding model radii. Our model radii are drawn from previously published calculations of coreless giant planets that have attained their asymptotic radii, and which have been tabulated for a range of planet masses and equilibrium temperatures. (We report a two-dimensional polynomial fitting function that accurately represents the models.) As expected, the model radii provide a statistically significant improvement over a null hypothesis that the sizes of giant planets are completely independent of mass and effective temperature. As is well known, however, fiducial models provide an insufficient explanation; the planetary radius anomalies, R ≡ Robs −Rpred, are strongly correlated with planetary equilibrium temperature. We find that the radius anomalies have a best-fit dependence, R ∝ Tαeff, with α = 1.4 ± 0.6. Incorporating this relation into the model radii leads to substantially less scatter in the radius correlation. The extra temperature dependence represents an important constraint on theoretical models for hot Jupiters. Using simple scaling arguments, we find support for the hypothesis of Batygin & Stevenson that this correlation can be attributed to a planetary heating mechanism that is mediated by magnetohydrodynamic coupling between the planetary magnetic field and near-surface flow that is accompanied by ohmic dissipation at adiabatic depth. Additionally, we find that the temperature dependence is likely too strong to admit kinetic heating as the primary source of anomalous energy generation within the majority of the observed transiting planets.
Lazorenko, P.F., Sahlmann, J., Séansan, D., Figueira, P., Lovis, C., Martin, E., Mayor, M., Pepe, F., Queloz, D., Rodler, F., Santos, N., Udry, S., 2011, "Astrometric search for a planet around VB 10," Astronomy and Astrophysics, 527, 25.
We observed VB 10 in August and September 2009 using the FORS2 camera of the VLT with the aim of measuring its astrometric motion and of probing for the presence of the announced planet VB 10b. We used the published STEPS astrometric positions of VB 10 over a timespan of 9 years, which allowed us to compare the expected motion of VB 10 due to parallax and proper motion with the observed motion and to compute precise deviations. The single-epoch precisions of our observations are about 0.1 mas, and the data showed no significant residual trend, while the presence of the planet should have induced an apparent proper motion greater than 10 mas yr-1. Subtraction of the predicted orbital motion from the observed data produces a strong trend in position residuals of VB 10. We estimated the probability that this trend is caused by random noise. After taking all the uncertainties into account and using Monte-Carlo resampling of the data, we are able to reject the existence of VB 10b with the announced mass of 6.4 MJ with a false alarm probability of only 5 ×10-4. A 3.2 MJ planet is also rejected with a false alarm probability of 0.023.
Libeskind, N.I., Knebe, A., Hoffman, Y., Gottlö, S., Yepes, G., Steinmetz, M., 2011, "The preferred direction of infalling satellite galaxies in the Local Group," Monthly Notices of the Royal Astronomical Society, 411, 1525-1535.
Using a high-resolution dark matter (DM) simulation of the Local Group, conducted within the framework of the Constrained Local UniversE Simulation (CLUES) project, we investigate the nature of how satellites of the Milky Way (MW) and M31 are accreted. Satellites of these two galaxies are accreted anisotropically on to the main haloes, entering the virial radius of their hosts, from specific 'spots' with respect to the large-scale structure. Furthermore, the material which is tidally stripped from these accreted satellites is also, at z= 0, distributed anisotropically and is characterized by an ellipsoidal subvolume embedded in the halo. The angular pattern created by the locus of satellite infall points and the projected z= 0 stripped dark matter is investigated within a coordinate system determined by the location of the Local Group companion and the simulated Virgo cluster across concentric shells ranging from 0.1 to 5 rvir. Remarkably, the principal axis of the ellipsoidal subvolume shows a coherent alignment extending from well within the halo to a few rvir. A spherical harmonics transform applied to the angular distributions confirms the visual impression: namely, the angular distributions of both the satellites entry points and stripped DM for both haloes are dominated by the l= 2 quadrupole term, whose major principal axis is approximately aligned across the shells considered. It follows that the outer (r > 0.5rvir) structure of the main haloes of the Local Group composed of stripped material is closely related to the cosmic web, within which it is embedded. Given the very plausible hypothesis that an important fraction of the stellar halo of the MW has been accreted from satellite galaxies, the present results can be directly applied to the stellar halo of the MW and M31. We predict that the remnants of tidally stripped satellites should be embedded in streams of material composed of dark matter and stars. The present results can therefore shed light on the existence of satellites embedded within larger streams of matter, such as the Segue 2 satellite.
Lissauer, J.J., Fabrycky, D.C., Ford, E.B., Borucki, W.J., Fressin, F., Marcy, G.W., Orosz, J.A., Rowe, J.F., Torres, G., Welsh, W.F., Batalha, N.M., Bryson, S.T., Buchhave, L.A., Caldwell, D.A., Carter, J.A., Charbonneau, D., Christiansen, J.L., Cochran, W.D., Desert, J.-M., Dunham, E.W., Fanelli, M.N., Fortney, J.J., Gautier, T.N., III, Geary, J.C., Gilliland, R.L., Haas, M.R., Hall, J.R., Holman, M.J., Koch, D.G., Latham, D.W., Lopez, E., McCauliff, S., Miller, N., Morehead, R.C., Quintana, E.V., Ragozzine, D., Sasselov, D., Short, D.R., Steffen, J.H., 2011, "A closely packed system of low-mass, low-density planets transiting Kepler-11," Nature, 470, 53-58.
When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation.
Luhman, K.L., Burgasser, A.J., Bochanski, J.J., 2011, "Discovery of a Candidate for the Coolest Known Brown Dwarf," The Astrophysical Journal, 730, L9.
We have used multi-epoch images from the Infrared Array Camera on board the Spitzer Space Telescope to search for substellar companions to stars in the solar neighborhood based on common proper motions. Through this work, we have discovered a faint companion to the white dwarf WD 0806-661. The comoving source has a projected separation of 130'', corresponding to 2500 AU at the distance of the primary (19.2 pc). If it is physically associated, then its absolute magnitude at 4.5 μm is ~1 mag fainter than the faintest known T dwarfs, making it a strong candidate for the coolest known brown dwarf. The combination of M 4.5 and the age of the primary (1.5 Gyr) implies an effective temperature of ~300 K and a mass of ~7 M Jupaccording to theoretical evolutionary models. The white dwarf's progenitor likely had a mass of ~2 M sun, and thus could have been born with a circumstellar disk that was sufficiently massive to produce a companion with this mass. Therefore, the companion could be either a brown dwarf that formed like a binary star or a giant planet that was born within a disk and has been dynamically scattered to a larger orbit.
Machida, M.N., Inutsuka, S.-i., Matsumoto, T., 2011, "Recurrent Planet Formation and Intermittent Protostellar Outflows Induced by Episodic Mass Accretion," The Astrophysical Journal, 729, 42.
The formation and evolution of a circumstellar disk in magnetized cloud cores are investigated from a prestellar core stage until ~104 yr after protostar formation. In the circumstellar disk, fragmentation first occurs due to gravitational instability in a magnetically inactive region, and substellar-mass objects appear. The substellar-mass objects lose their orbital angular momenta by gravitational interaction with the massive circumstellar disk and finally fall onto the protostar. After this fall, the circumstellar disk increases its mass by mass accretion and again induces fragmentation. The formation and falling of substellar-mass objects are repeated in the circumstellar disk until the end of the main accretion phase. In this process, the mass of the fragments remains small, because the circumstellar disk loses its mass by fragmentation and subsequent falling of fragments before it becomes very massive. In addition, when fragments orbit near the protostar, they disturb the inner disk region and promote mass accretion onto the protostar. The orbital motion of substellar-mass objects clearly synchronizes with the time variation of the accretion luminosity of the protostar. Moreover, as the objects fall, the protostar shows a strong brightening for a short duration. The intermittent protostellar outflows are also driven by the circumstellar disk whose magnetic field lines are highly tangled owing to the orbital motion of fragments. The time-variable protostellar luminosity and intermittent outflows may be a clue for detecting planetary-mass objects in the circumstellar disk.
Machida, M.N., Matsumoto, T., 2011, "The origin and formation of the circumstellar disc," Monthly Notices of the Royal Astronomical Society, 284.
The formation and evolution of the circumstellar disc in the collapsing molecular cloud with and without magnetic field is investigated from the pre-stellar stage resolving both the molecular cloud core and the protostar itself. In the collapsing cloud core, the first (adiabatic) core appears prior to the protostar formation. Reflecting the thermodynamics of the collapsing gas, the first core is much more massive than the protostar. When the molecular cloud has no angular momentum, the first core falls on to the protostar and disappears a few years after the protostar formation. On the other hand, when the molecular cloud has an angular momentum, the first core does not disappear even after the protostar formation, and directly evolves into the circumstellar disc with a Keplerian rotation. There are two paths for the formation of the circumstellar disc. When the initial cloud has a considerably small rotational energy, two nested discs appear just after the protostar formation. During the early main accretion phase, the inner disc increases its size and merges with the outer disc (i.e. first core) to form a single circumstellar disc with a Keplerian rotation. On the other hand, when the molecular cloud has a rotational energy comparable to observations, a single centrifugally supported disc that corresponds to the first core already exists prior to the protostar formation. In such a cloud, the first core density gradually increases, maintaining the Keplerian rotation and forms the protostar inside it. The magnetic field rarely affects the early formation of the circumstellar disc because the magnetic field dissipates in the high-density gas region where the circumstellar disc forms. As a result, in any case, the protostar at its formation is already surrounded by a massive circumstellar disc. The circumstellar disc is about 10-100 times more massive than the protostar in the main accretion phase. Such discs are favourable sites for the formation of binary companions and gas-giant planets.
Maciejewski, G., Dimitrov, D., Neuhäer, R., Tetzlaff, N., Niedzielski, A., Raetz, S., Chen, W.P., Walter, F., Marka, C., Baar, S., KrejcováT., Budaj, J., Krushevska, V., Tachihara, K., Takahashi, H., Mugrauer, M., 2011, "Transit timing variation and activity in the WASP-10 planetary system," Monthly Notices of the Royal Astronomical Society, 411, 1204-1212.
Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems that harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009, we collected nine light curves of eight transits of the exoplanet WASP-10b. Combining these data with those published, we have found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models, which reproduce the observed variations of timing residuals, were identified by numerical simulations. We have found that the configuration with an additional planet with a mass of ~0.1 MJ and an orbital period of ~5.23 d, located close to the outer 5 : 3 mean motion resonance, is the most likely scenario. If the second planet is a transiter, the estimated flux drop will be ~0.3 per cent and can be observed with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and the rotation of the star affect the radial-velocity curve, giving rise to a spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270 ± 80 Myr old. This young age can explain the large radius reported for WASP-10b.
Malmberg, D., Davies, M.B., Heggie, D.C., 2011, "The effects of fly-bys on planetary systems," Monthly Notices of the Royal Astronomical Society, 411, 859-877.
Most of the observed extrasolar planets are found on tight and often eccentric orbits. The high eccentricities are not easily explained by planet-formation models, which predict that planets should be on rather circular orbits. Here we explore whether fly-bys involving planetary systems with properties similar to those of the gas giants in the Solar system can produce planets with properties similar to the observed planets. Using numerical simulations, we show that fly-bys can cause the immediate ejection of planets, and sometimes also lead to the capture of one or more planets by the intruder. More common, however, is that fly-bys only perturb the orbits of planets, sometimes leaving the system in an unstable state. Over time-scales of a few million to several hundred million years after the fly-by, this perturbation can trigger planet-planet scatterings, leading to the ejection of one or more planets. For example, in the case of the four gas giants of the Solar system, the fraction of systems from which at least one planet is ejected more than doubles in 108 yr after the fly-by. The remaining planets are often left on more eccentric orbits, similar to the eccentricities of the observed extrasolar planets. We combine our results of how fly-bys affect Solar-system-like planetary systems, with the rate at which encounters in young stellar clusters occur. For example, we measure the effects of fly-bys on the four gas giants in the Solar system. We find, that for such systems, between 5 and 15 per cent suffer ejections of planets in 108 yr after fly-bys in typical open clusters. Thus, encounters in young stellar clusters can significantly alter the properties of any planets orbiting stars in clusters. As a large fraction of stars which populate the solar neighbourhood form in stellar clusters, encounters can significantly affect the properties of the observed extrasolar planets.
Martin, R.G., Lubow, S.H., 2011, "Tidal truncation of circumplanetary discs," Monthly Notices of the Royal Astronomical Society, 202.
We analyse some properties of circumplanetary discs. Flow through such discs may provide most of the mass to gas giant planets, and such discs are likely sites for the formation of regular satellites. We model these discs as accretion discs subject to the tidal forces of the central star. The tidal torques from the star remove the disc angular momentum near the disc outer edge and permit the accreting disc gas to lose angular momentum at the rate appropriate for steady accretion. Circumplanetary discs are truncated near the radius where periodic ballistic orbits cross, where tidal forces on the disc are strong. This radius occurs at approximately 0.4rH for the planet Hill radius rH. During the T Tauri stage of disc accretion, the disc is fairly thick with aspect ratio H/r≳ 0.2 and the disc edge tapering occurs over a radial scale ~H~ 0.1rH. The disc fluid equations can be rescaled in the Hill approximation to a form similar to the flow equations for a disc in a binary star system with a mass ratio of unity. For a circular or slightly eccentric orbit planet, no significant resonances lie within the main body of the disc. Tidally driven waves involving resonances none the less play an important role in truncating the disc, especially when it is fairly thick. We model the disc structure using one-dimensional time-dependent and steady-state models and also two-dimensional smoothed particle hydrodynamics simulations. The circumplanetary disc structure depends on the variation of the disc turbulent viscosity with radius and is insensitive to the angular distribution of the accreting gas. Dead zones may occur within the circumplanetary disc and result in density structures. If the disc is turbulent throughout, the predicted disc structure near the location of the regular Jovian and Saturnian satellites is smooth with no obvious feature that would favour formation at their current locations. It may be possible that substructure, such as due to variations in the disc turbulence, could lead to the trapping of migrating satellites.
Matsuo, T., Traub, W.A., Hattori, M., Tamura, M., 2011, "A New Concept for Direct Imaging and Spectral Characterization of Exoplanets in Multi-planet Systems," The Astrophysical Journal, 729, 50.
We present a novel method for direct detection and characterization of exoplanets from space. This method uses four collecting telescopes, combined with phase chopping and a spectrometer, with observations on only a few baselines rather than on a continuously rotated baseline. Focusing on the contiguous wavelength spectra of typical exoplanets, the (u, v) plane can be simultaneously and uniformly filled by recording the spectrally resolved signal. This concept allows us to perfectly remove speckles from reconstructed images. For a target comprising a star and multiple planets, observations on three baselines are sufficient to extract the position and spectrum of each planet. Our simulations show that this new method allows us to detect an analog Earth around a Sun-like star at 10 pc and to acquire its spectrum over the wavelength range from 8 to 19 ?m with a high spectral resolution of 100. This method allows us to fully characterize an analog Earth and to similarly characterize each planet in multi-planet systems.
Meschiari, S., Laughlin, G., Vogt, S.S., Butler, R.P., Rivera, E.J., Haghighipour, N., Jalowiczor, P., 2011, "The Lick-Carnegie Survey: Four New Exoplanet Candidates," The Astrophysical Journal, 727, 117.
We present new precise HIRES radial velocity (RV) data sets of ﬁve nearby stars obtained at Keck Observatory. HD31253, HD 218566, HD 177830, HD 99492, and HD 74156 are host stars of spectral classes F through K and show RV variations consistent with new or additional planetary companions in Keplerian motion. The orbital parameters of the candidate planets in the ﬁve planetary systems span minimum masses of Msin i = 27.43 M⊕ to 8.28 MJ , periods of 17.05.4696.95 days and eccentricities ranging from circular to extremely eccentric (e ≈ 0.63). The ﬁfth star, HD 74156, was known to have both a 52 day and a 2500 day planet, and was claimed to also harbor a third planet at 336 days, in apparent support of the .Packed Planetary System. hypothesis. Our greatly expanded data set for HD 74156 provides strong conﬁrmation of both the 52 day and 2500 day planets, but strongly contradicts the existence of a 336 day planet, and offers no signiﬁcant evidence for any other planets in the system
Messenger, C., Lommen, A., Demorest, P., Ransom, S., 2011, "A Bayesian parameter estimation approach to pulsar time-of-arrival analysis," Classical and Quantum Gravity, 28, 5001.
The increasing sensitivities of pulsar timing arrays to ultra-low frequency (nHz) gravitational waves promise to achieve direct gravitational wave (GW) detection within the next 5-10 years. While there are many parallel efforts being made in the improvement of telescope sensitivity, the detection of stable millisecond pulsars and the improvement of the timing software, there are reasons to believe that the methods used to accurately determine the time-of-arrival (TOA) of pulses from radio pulsars can be improved upon. More specifically, the determination of the uncertainties on these TOAs, which strongly affect the ability to detect GWs through pulsar timing, may be unreliable. We propose two Bayesian methods for the generation of pulsar TOAs starting from pulsar 'search-mode' data and pre-folded data. These methods are applied to simulated toy-model examples and in this initial work we focus on the issue of uncertainties in the folding period. The final results of our analysis are expressed in the form of posterior probability distributions on the signal parameters (including the TOA) from a single observation.
Migaszewski, C., Goździewski, K., 2011, "The non-resonant, relativistic dynamics of circumbinary planets," Monthly Notices of the Royal Astronomical Society, 411, 565-583.
We investigate a non-resonant, three-dimensional (spatial) model of a hierarchical system composed of a point-mass stellar (or substellar) binary and a low-mass companion (a circumbinary planet or a brown dwarf). We take into account the leading relativistic corrections to the Newtonian gravity. The secular model of the system relies on the expansion of the perturbing Hamiltonian in terms of the ratio of semi-major axes α, averaged over the mean anomalies. We found that a low-mass object in a distant orbit may excite a large eccentricity of the inner binary when the mutual inclination of the orbits is larger than about 60°. This is related to the strong instability caused by a phenomenon that acts similarly to the Lidov.Kozai resonance (LKR). The secular system may be strongly chaotic and its dynamics unpredictable over long-term time-scales. Our study shows that in the Jupiter-or brown-dwarf-mass regime of the low-mass companion, the restricted model does not properly describe the long-term dynamics in the vicinity of the LKR. The relativistic correction is significant for the parametric structure of a few families of stationary solutions in this problem, in particular for direct orbit configurations (with mutual inclination less than 90°). We found that the dynamics of hierarchical systems with small α∼ 0.01 may be qualitatively different in the realms of Newtonian (classic) and relativistic models. This holds true even for relatively large masses of the secondaries
Miyake, N., Sumi, T., Dong, S., Street, R., Mancini, L., Gould, A., Bennett, D.P., Tsapras, Y., Yee, J.C., Albrow, M.D., Bond, I.A., FouquéP., Browne, P., Han, C., Snodgrass, C., Finet, F., Furusawa, K., Harpsø., Allen, W., Hundertmark, M., Freeman, M., Suzuki, D., Abe, F., Botzler, C.S., Douchin, D., Fukui, A., Hayashi, F., Hearnshaw, J.B., Hosaka, S., Itow, Y., Kamiya, K., Kilmartin, P.M., Korpela, A., Lin, W., Ling, C.H., Makita, S., Masuda, K., Matsubara, Y., Muraki, Y., Nagayama, T., Nishimoto, K., Ohnishi, K., Perrott, Y.C., Rattenbury, N., Saito, T., Skuljan, L., Sullivan, D.J., Sweatman, W.L., Tristram, P.J., Wada, K., Yock, P.C.M., Collaboration, M., Bolt, G., Bos, M., Christie, G.W., DePoy, D.L., Drummond, J., Gal-Yam, A., Gaudi, B.S., Gorbikov, E., Higgins, D., Hwang, K.-H., Janczak, J., Kaspi, S., Lee, C.-U., Koo, J.-R., Koz?owski, S., Lee, Y., Mallia, F., Maury, A., Maoz, D., McCormick, J., Monard, L.A.G., Moorhouse, D., Muñ J.A., Natusch, T., Ofek, E.O., Pogge, R.W., Polishook, D., Santallo, R., Shporer, A., Spector, O., Thornley, G., Collaboration, F., Allan, A., Bramich, D.M., Horne, K., Kains, N., Steele, I., Collaboration, R., Bozza, V., Burgdorf, M.J., Calchi Novati, S., Dominik, M., Dreizler, S., Glitrup, M., Hessman, F.V., Hinse, T.C., Jøsen, U.G., Liebig, C., et al., 2011, "A Sub-Saturn Mass Planet, MOA-2009-BLG-319Lb," The Astrophysical Journal, 728, 120.
We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K- or M-dwarf star in the inner Galactic disk or Galactic bulge. The high-cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high-magnification event approximately 24 hr prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 ± 0.02) ×10.4 and a separation of d = 0.97537 ± 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t E, and angular Einstein radius, θE, along with a standard Galactic model indicates a host star mass of M L = 0.38+0.34 .0.18 M and a planet mass of M p = 50+44 .24 M ⊕, which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4+1.2 .0.6 AU and a distance to the planetary system of D L = 6.1+1.1 .1.2 kpc. This separation is ~2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing
Moerchen, M.M., Churcher, L.J., Telesco, C.M., Wyatt, M., Fisher, R.S., Packham, C., 2011, "Asymmetric heating of the HR 4796A dust ring due to pericenter glow," Astronomy and Astrophysics, 526, 34.
We have obtained new resolved images of the well-studied HR 4796A dust ring at 18 and 25 mm with the 8-m Gemini telescopes. These images confirm the previously observed spatial extent seen in mid-IR, near-IR, and optical images of the source. We detect brightness and temperature asymmetries such that dust on the NE side is both brighter and warmer than dust in the SW. We show that models of so-called pericenter glow account for these asymmetries, thus both confirming and extending our previous analyses. In this scenario, the center of the dust ring is offset from the star due to gravitational perturbations of a body with an eccentric orbit that has induced a forced eccentricity on the dust particle orbits. Models with 2-mm silicate dust particles and a forced eccentricity of 0.06 simultaneously fit the observations at both wavelengths. We also show that parameters used to characterize the thermal-emission properties of the disk can also account for the disk asymmetry observed in shorter-wavelength scattered-light images.
Mordasini, C., Mayor, M., Udry, S., Lovis, C., Séansan, D., Benz, W., Bertaux, J.-L., Bouchy, F., Lo Curto, G., Moutou, C., Naef, D., Pepe, F., Queloz, D., Santos, N.C., 2011, "The HARPS search for southern extra-solar planets. XXIV. Companions to HD 85390, HD 90156, and HD 103197: a Neptune analog and two intermediate-mass planets," Astronomy and Astrophysics, 526, 111.
We report the detection of three new extrasolar planets orbiting the solar type stars HD 85390, HD 90156 and HD 103197 with the HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla observatory.
Moutou, C., Mayor, M., Lo Curto, G., Séansan, D., Udry, S., Bouchy, F., Benz, W., Lovis, C., Naef, D., Pepe, F., Queloz, D., Santos, N.C., Sousa, S.G., 2011, "The HARPS search for southern extra-solar planets. XXVII. Seven new planetary systems," Astronomy and Astrophysics, 527, 63.
We are conducting a planet search survey with HARPS since seven years. The volume-limited stellar sample includes all F2 to M0 main-sequence stars within 57.5 pc, where extrasolar planetary signatures are systematically searched for with the radial-velocity technics. In this paper, we report the discovery of new substellar companions of seven main-sequence stars and one giant star, detected through multiple Doppler measurements with the instrument HARPS installed on the ESO 3.6 m telescope, La Silla, Chile. These extrasolar planets orbit the stars
Mustill, A.J., Wyatt, M.C., 2011, "A general model of resonance capture in planetary systems: first- and second-order resonances," Monthly Notices of the Royal Astronomical Society, 277.
Mean motion resonances are a common feature of both our own Solar system and of extrasolar planetary systems. Bodies can be trapped in resonance when their orbital semimajor axes change, for instance when they migrate through a protoplanetary disc. We use a Hamiltonian model to thoroughly investigate the capture behaviour for first- and second-order resonances. Using this method, all resonances of the same order can be described by one equation, with applications to specific resonances by appropriate scaling. We focus on the limit where one body is a massless test particle and the other a massive planet. We quantify how the probability of capture into a resonance depends on the relative migration rate of the planet and particle, and the particle.s eccentricity. Resonant capture fails for high migration rates, and has decreasing probability for higher eccentricities, although for certain migration rates, capture probability peaks at a finite eccentricity. More massive planets can capture particles at higher eccentricities and migration rates. We also calculate libration amplitudes and the offset of the libration centres for captured particles, and the change in eccentricity if capture does not occur. Libration amplitudes are higher for larger initial eccentricity. The model allows for a complete description of a particle.s behaviour as it successively encounters several resonances. Data files containing the integration grid output will be available online. We discuss implications for several scenarios: (i) Planet migration through gas discs trapping other planets or planetesimals in resonances: we find that, with classical prescriptions for Type I migration, capture into second-order resonances is not possible, and lower mass planets or those further from the star should trap objects in first-order resonances closer to the planet than higher mass planets or those closer to the star. For fast enough migration, a planet can trap no objects into its resonances. We suggest that the present libration amplitude of planets may be a signature of their eccentricities at the epoch of capture, with high libration amplitudes suggesting high eccentricity (e.g. HD 128311). (ii) Planet migration through a debris disc: we find the resulting dynamical structure depends strongly both on migration rate and on planetesimal eccentricity. Translating this to spatial structure, we expect clumpiness to decrease from a significant level at e ? 0.01 to non-existent at e ? 0.1. (iii) Dust migration through Poynting-Robertson (PR) drag: we predict that Mars should have its own resonant ring of particles captured from the zodiacal cloud, and that the capture probability is ?25 per cent that of the Earth, consistent with published upper limits for its resonant ring. To summarize, the Hamiltonian model will allow quick interpretation of the resonant properties of extrasolar planets and Kuiper Belt Objects, and will allow synthetic images of debris disc structures to be quickly generated, which will be useful for predicting and interpreting disc images made with Atacama Large Millimeter Array (ALMA), Darwin/Terrestrial Planet Finder (TPF) or similar missions.
Na, X.S., Wang, N., Yuan, J.P., Liu, Z.Y., Esamdin, A., Pan, J., Xu, R.X., 2011, "Hurst parameter analysis of radio pulsar timing residuals," Monthly Notices of the Royal Astronomical Society, 163.
We analyse the timing residuals for 50 pulsars observed using the Nanshan 25-m radio telescope at Urumqi Observatory by determining the Hurst parameter for each data set using the rescaled range method. These pulsars have been observed over a time span of 5-8 yr and have been selected to have timing residuals that resemble white noise rather than smooth curves. The results are compared with those for shuffled residual series. Despite the noise-like appearance, some timing residual series showed Hurst parameters that deviated significantly from the shuffled series. We conclude that Hurst parameter analysis is capable of detecting long-term memory in timing residuals.
Namouni, F., 2011, "On dynamical friction in a gaseous medium with a boundary," Astrophysics and Space Science, 331, 575-595.
Dynamical friction arises from the interaction of a perturber and the gravitational wake it excites in the ambient medium. We study the effects of the presence of a boundary on dynamical friction by studying analytically the interaction of perturber with uniform rectilinear motion in a uniform homogeneous medium with a reflecting planar boundary. Wake reflection at a medium's boundary may occur at the edges of truncated disks perturbed by planetary or stellar companions as well as in numerical simulations of planet-disk interaction with no-outflow boundary conditions. In this paper, we show that the presence of the boundary modifies the behaviour of dynamical friction significantly. We find that perturbers are invariably pushed away from the boundary and reach a terminal subsonic velocity near Mach 0.37 regardless of initial velocity. Dynamical friction may even be reversed for Mach numbers less than 0.37 thereby accelerating instead of decelerating the perturber. Perturbers moving parallel to the boundary feel additional friction orthogonal to the direction of motion that is much stronger than the standard friction along the direction of motion. These results indicate that the common use of the standard Chandrasekhar formula as a short hand estimate of dynamical friction may be inadequate as observed in various numerical simulations.
Nascimbeni, V., Piotto, G., Bedin, L.R., Damasso, M., 2011, "TASTE: The Asiago Search for Transit timing variations of Exoplanets. I. Overview and improved parameters for HAT-P-3b and HAT-P-14b," Astronomy and Astrophysics, 527, 85.
A promising method for detecting earth-sized exoplanets is the timing analysis of a known transit. The technique allows a search for variations in either the transit duration or the center induced by the perturbation of a third body, e.g. a second planet or an exomoon. By applying this method, the TASTE (The Asiago search for transit timing variations of Exoplanets) project will collect high-precision, short-cadence light curves for a selected sample of transits by using imaging differential photometry at the Asiago 1.82 m telescope. The first light curves show that our project can achieve a competitive timing accuracy, as well as a significant improvement of the orbital parameters. We derived refined ephemerides for HAT-P-3b and HAT-P-14b with a timing accuracy of 11 and 25 s, respectively. Photometric data is only a vailable in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsweb.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A85
Oberti, P., Pocart, B., 2011, "Intermediary orbits for oscillating motions," Astrophysics and Space Science, 49.
Hamiltonian approximations generally result from series expansions and truncations at different orders. But other ways are possible, and some of them, as the one this paper tries to explore, can speed up Hamiltonian computations and prove useful for studies involving extensive developments, for example solar system bodies with complex dynamics or requiring accurate ephemeris for observational purposes. Reflecting a property of the frequency of motion of the pendulum's Hamiltonian, a fast convergent algorithm aimed to build pendulum approximations was outlined in a completely different way that the classical development in powers of the libration angle. With convenient initial conditions, the first two steps of the algorithm lead to approximate Hamiltonians explicitly expressed in the normalizing action variable and offering solutions easily obtained through Kepler-like equations, hence providing useful intermediary orbits for the Lie transformation algorithm. Numerical checks showed a good efficiency and consistency of these solutions up to rather large libration amplitudes: for libration angles up to 300 degrees, only half the steps required by the classical development algorithm sufficed for this one to mimic the pendulum, and the second step's solution outrun its classical counterpart up to 90 degrees.
Ouyang, T., Yan, D., 2011, "Periodic solutions with alternating singularities in the collinear four-body problem," Celestial Mechanics and Dynamical Astronomy, 109, 229-239.
This paper gives an analytic proof of the existence of Schubart-like orbit, a periodic orbit with singularities in the symmetric collinear four-body problem. In each period of the Schubart-like orbit, there is a binary collision (BC) between the inner two bodies and a simultaneous binary collision (SBC) of the two clusters on both sides of the origin. The system is regularized and the existence is proved by using a .turning point. technique and a continuity argument on differential equations of the regularized Hamiltonian.
Pá A., Sáeczky, K., Szabó.M., Szing, A., Kiss, L.L., Mez?, G., Regá, Z., 2011, "Transit timing variations in the HAT-P-13 planetary system," Monthly Notices of the Royal Astronomical Society, L220.
In this Letter we present observations of recent HAT-P-13b transits. The combined analysis of published and newly obtained transit epochs shows evidence for significant transit timing variations (TTVs) since the last publicly available ephemerides. Variation of transit timings results in a sudden switch of transit times. The detected full range of TTV spans ≈0.015 d, which is significantly more than the known TTV events exhibited by hot Jupiter. If we have detected a periodic process, its period should be at least ≈3 yr because there are no signs of variations in the previous observations. This argument makes unlikely that the measured TTV is due to perturbations by HAT-P-13c.
Payne, M.J., Ford, E.B., 2011, "An Analysis of Jitter and Transit Timing Variations in the HAT-P-13 System," The Astrophysical Journal, 729, 98.
If the two planets in the HAT-P-13 system are coplanar, the orbital states provide a probe of the internal planetary structure. Previous analyses of radial velocity and transit timing data for the system suggested that the observational constraints on the orbital states were rather small. We reanalyze the available data, treating the jitter as an unknown MCMC parameter, and find that a wide range of jitter values are plausible, hence the system parameters are less well constrained than previously suggested. For slightly increased levels of jitter (~4.5 m s.1), the eccentricity of the inner planet can be in the range 0 < e inner< 0.07, the period and eccentricity of the outer planet can be 440 days < P outer < 470 days and 0.55 < e outer < 0.85, respectively, while the relative pericenter alignment, η, of the planets can take essentially any value .180° < η < +180°. It is therefore difficult to determine whether e inner and η have evolved to a fixed-point state or a limit cycle or to use e inner to probe the internal planetary structure. We perform various transit timing variation (TTV) analyses, demonstrating that current constraints merely restrict e outer < 0.85, and rule out relative planetary inclinations within ~2° of i rel = 90°, but that future observations could significantly tighten the restriction on both these parameters. We demonstrate that TTV profiles can readily distinguish the theoretically favored inclinations of i rel = 0° and 45°, provided that sufficiently precise and frequent transit timing observations of HAT-P-13b can be made close to the pericenter passage of HAT-P-13c. We note the relatively high probability that HAT-P-13c transits and suggest observational dates and strategies.
Pont, F., Aigrain, S., Zucker, S., 2011, "Reassessing the radial-velocity evidence for planets around CoRoT-7," Monthly Notices of the Royal Astronomical Society, 411, 1953-1962.
CoRoT-7 is an 11 th magnitude K-star whose light curve shows transits with a depth of 0.3 mmag and a period of 0.854 d, superimposed on variability at the 1 per cent level, due to the modulation of evolving active regions with the star's 23-d rotation period. In this paper, we revisit the published HARPS radial-velocity (RV) measurements of the object, which were previously used to estimate the companion mass, but have been the subject of ongoing debate.
We build a realistic model of the star's activity during the HARPS observations, by fitting simultaneously the linewidth (as measured by the width of the cross-correlation function) and the line bisector, and use it to evaluate the contribution of activity to the RV variations. The data show clear evidence of errors above the level of the formal uncertainties, which are accounted for neither by activity nor by any plausible planet model and which increase rapidly with a decreasing signal-to-noise ratio (S/N) of the spectra. We cite evidence of similar systematics in mid-S/N spectra of other targets obtained with HARPS and other high-precision RV spectrographs, and discuss possible sources. Allowing for these, we re-evaluate the semi-amplitude of the CoRoT-7b signal, finding Kb= 1.6 ± 1.3 m s-1, a tentative detection with a much reduced significance (1.2σ) compared to previous estimates. We also argue that the combined presence of activity and additional errors precludes a meaningful search for additional low-mass companions, despite previous claims to the contrary.
Taken at face value, our analysis points to a lower density for CoRoT-7b, the 1σ mass range spanning 1-4 M ⊕ and allowing for a wide range of bulk compositions. In particular, an ice-rich composition is compatible with the RV constraints. More generally, this study highlights the importance of a realistic treatment of both activity and uncertainties, particularly in the medium S/N regime, which applies to most small planet candidates from CoRoT and Kepler.
Rambaux, N., van Hoolst, T., Karatekin, Ö, 2011, "Librational response of Europa, Ganymede, and Callisto with an ocean for a non-Keplerian orbit," Astronomy and Astrophysics, 527, 118.
Context. The Galilean satellites Europa, Ganymede, and Callisto are thought to harbor a subsurface ocean beneath an ice shell but its properties, such as the depth beneath the surface, have not been well constrained. Future geodetic observations with, for example, space missions like the Europa Jupiter System Mission (EJSM) of NASA and ESA may refine our knowledge about the shell and ocean.
Aims: Measurement of librational motion is a useful tool for detecting an ocean and characterizing the interior parameters of the moons. The objective of this paper is to investigate the librational response of Galilean satellites, Europa, Ganymede, and Callisto assumed to have a subsurface ocean by taking the perturbations of the Keplerian orbit into account. Perturbations from a purely Keplerian orbit are caused by gravitational attraction of the other Galilean satellites, the Sun, and the oblateness of Jupiter.
Methods: We use the librational equations developed for a satellite with a subsurface ocean in synchronous spin-orbit resonance. The orbital perturbations were obtained from recent ephemerides of the Galilean satellites.
Results: We identify the wide frequency spectrum in the librational response for each Galilean moon. The librations can be separated into two groups, one with short periods close to the orbital period, and a second group of long-period librations related to the gravitational interactions with the other moons and the Sun. Long-period librations can have amplitudes as large as or even larger than the amplitude of the main libration at orbital period for the Keplerian problem, implying the need to introduce them in analyses of observations linked to the rotation. The amplitude of the short-period librations contains information on the interior of the moons, but the amplitude associated with long periods is almost independent of the interior at first order in the low frequency. For Europa, we identified a short-period libration with period close to twice the orbital period, which could have been resonantly amplified in the history of Europa. For Ganymede, we also found a possible resonance between a proper period and a forced period when the icy shell thickness is around 50 km. The librations of Callisto are dominated by solar perturbations.
Reffert, S., Quirrenbach, A., 2011, "Mass constraints on substellar companion candidates from the re-reduced Hipparcos intermediate astrometric data: nine confirmed planets and two confirmed brown dwarfs," Astronomy and Astrophysics, 527, 140.
Context. The recently completed re-reduction of the Hipparcos data by van Leeuwen (2007a, Astrophysics and Space Science Library, 350) makes it possible to search for the astrometric signatures of planets and brown dwarfs known from radial velocity surveys in the improved Hipparcos intermediate astrometric data.
Aims: Our aim is to put more significant constraints on the orbital parameters which cannot be derived from radial velocities alone, i.e. the inclination and the longitude of the ascending node, than was possible before. The determination of the inclination in particular allows to calculate an unambiguous companion mass, rather than the lower mass limit which can be obtained from radial velocity measurements.
Methods: We fitted the astrometric orbits of 310 substellar companions around 258 stars, which were all discovered via the radial velocity method, to the Hipparcos intermediate astrometric data provided by van Leeuwen.
Results: Even though the astrometric signatures of the companions cannot be detected in most cases, the Hipparcos data still provide lower limits on the inclination for all but 67 of the investigated companions, which translates into upper limits on the masses of the unseen companions. For nine companions the derived upper mass limit lies in the planetary and for 75 companions in the brown dwarf mass regime, proving the substellar nature of those objects. Two of those objects have minimum masses also in the brown dwarf regime and are thus proven to be brown dwarfs. The confirmed planets are the ones around Pollux (β Gem b), ϵ Eri b, ϵ Ret b, μ Ara b, υ And c and d, 47 UMa b, HD 10647 b and HD 147513 b. The confirmed brown dwarfs are HD 137510 b and HD 168443 c. In 20 cases, the astrometric signature of the substellar companion was detected in the Hipparcos data, resulting in reasonable constraints on inclination and ascending node. Of these 20 companions, three are confirmed as planets or lightweight brown dwarfs (HD 87833 b, ι Dra b, and γ Cep b), two as brown dwarfs (HD 106252 b and HD 168443 b), and four are low-mass stars (BD -04 782 b, HD 112758 b, ρ CrB b, and HD169822 b). Of the others, many are either brown dwarfs or very low mass stars. For ϵ Eri, we derive a solution which is very similar to the one obtained using Hubble Space Telescope data.
Rosen, R., McLaughlin, M.A., Thompson, S.E., 2011, "A Non-radial Oscillation Model for Pulsar State Switching," The Astrophysical Journal, 728, L19.
Pulsars are unique astrophysical laboratories because of their clock-like timing precision, providing new ways to test general relativity and detect gravitational waves. One impediment to high-precision pulsar timing experiments is timing noise. Recently, Lyne et al. showed that the timing noise in a number of pulsars is due to quasi-periodic fluctuations in the pulsars' spin-down rates and that some of the pulsars have associated changes in pulse profile shapes. Here we show that a non-radial oscillation model based on asteroseismological theory can explain these quasi-periodic fluctuations. Application of this model to neutron stars will increase our knowledge of neutron star emission and neutron star interiors and may improve pulsar timing precision.
Sáhez, P., Scheeres, D.J., 2011, "Simulating Asteroid Rubble Piles with A Self-gravitating Soft-sphere Distinct Element Method Model," The Astrophysical Journal, 727, 120.
This paper applies a soft-sphere distinct element method Granular Dynamics code to simulate asteroid regolith and rubble piles. Applications to regolith studies in low gravity are also studied. Then an algorithm to calculate self-gravity is derived and incorporated for full-scale simulations of rubble-pile asteroids using Granular Dynamics techniques. To test its validity, the algorithm's results are compared with the exact direct calculation of the gravitational forces. Further avenues to improve the performance of the algorithm are also discussed.
Savransky, D., Cady, E., Kasdin, N.J., 2011, "Parameter Distributions of Keplerian Orbits," The Astrophysical Journal, 728, 66.
Starting with just the assumption of uniformly distributed orbital orientations, we derive expressions for the distributions of the Keplerian orbital elements as functions of arbitrary distributions of eccentricity and semimajor axis. We present methods for finding the probability density functions of the true anomaly, eccentric anomaly, orbital radius, and other parameters used in describing direct planetary observations. We also demonstrate the independence of the distribution of phase angle, which is highly significant in the study of direct searches, and present examples validating the derived expressions.
Saynisch, J., Wenzel, M., Schrö, J., 2011, "Assimilation of Earth rotation parameters into a global ocean model: length of day excitation," Journal of Geodesy, 85, 67-73.
Changes in the oceanic current system and in the oceanic mass distribution alter, together with other processes, the state of the Earth's rotation. This state is characterized by the length of day (LOD) and the tilt of the pole-to-pole axis. The aim of our study was to derive the respective governing physical mechanisms in the ocean. Therefore, Earth rotation observations were assimilated into a global circulation model of the ocean. Although assimilation is a well-established tool in climate science, the assimilation of Earth rotation observations into a global ocean model was done here for the first time. Prior to the assimilation, the Earth rotation observations were projected onto the angular momentum of the ocean. Non-oceanic contributions were removed. The result of the subsequent assimilation procedure is a time varying ocean model state that reproduces the projected Earth rotation observations well. This solution was studied to understand the oceanic generation of Earth rotation deviations and to identify governing physical mechanisms. This paper focuses on LOD anomalies although polar motion was assimilated simultaneously. Our results indicate that changes in the oceanic LOD excitation are mostly attributed to changes in total ocean mass. Changes in the spatial distribution of ocean mass turned out to have a minor contribution to the LOD deviations. The same applies to changes in the current system.
Shaw, D.J., Barrow, J.D., 2011, "Testable solution of the cosmological constant and coincidence problems," Physical Review D, 83, 43518.
We present a new solution to the cosmological constant (CC) and coincidence problems in which the observed value of the CC, Λ, is linked to other observable properties of the Universe. This is achieved by promoting the CC from a parameter that must be specified, to a field that can take many possible values. The observed value of Λ≈(9.3Gyrs)-2 [≈10-120 in Planck units] is determined by a new constraint equation which follows from the application of a causally restricted variation principle. When applied to our visible Universe, the model makes a testable prediction for the dimensionless spatial curvature of Ωk0=-0.0056(ζb/0.5), where ζb~1/2 is a QCD parameter. Requiring that a classical history exist, our model determines the probability of observing a given Λ. The observed CC value, which we successfully predict, is typical within our model even before the effects of anthropic selection are included. When anthropic selection effects are accounted for, we find that the observed coincidence between tΛ=Λ-1/2 and the age of the Universe, tU, is a typical occurrence in our model. In contrast to multiverse explanations of the CC problems, our solution is independent of the choice of a prior weighting of different Λ values and does not rely on anthropic selection effects. Our model includes no unnatural small parameters and does not require the introduction of new dynamical scalar fields or modifications to general relativity, and it can be tested by astronomical observations in the near future.
Shevchenko, I.I., 2011, "The Kepler map in the three-body problem," New Astronomy, 16, 94-99.
The Kepler map was derived by Petrosky (1986) and Chirikov and Vecheslavov (1986) as a tool for description of the long-term chaotic orbital behaviour of the comets in nearly parabolic motion. It is a two-dimensional area-preserving map, describing the motion of a comet in terms of energy and time. Its second equation is based on Kepler.s third law, hence the title of the map. Since 1980s the Kepler map has become paradigmatic in a number of applications in celestial mechanics and atomic physics. It represents an important kind of general separatrix maps. Petrosky and Broucke (1988) used refined methods of mathematical physics to derive analytical expressions for its single parameter. These methods became available only in the second half of the 20th century, and it may seem that the map is inherently a very modern mathematical tool. With the help of the Jacobi integral I show that the Kepler map, including analytical formulae for its parameter, can be derived by quite elementary methods. The prehistory and applications of the Kepler map are considered and discussed.
Sicardy, B., Bolt, G., Broughton, J., Dobosz, T., Gault, D., Kerr, S., Bérd, F., Frappa, E., Lecacheux, J., Peyrot, A., Teng-Chuen-Yu, J.-P., Beisker, W., Boissel, Y., Buckley, D., Colas, F., de Witt, C., Doressoundiram, A., Roques, F., Widemann, T., Gruhn, C., Batista, V., Biggs, J., Dieters, S., Greenhill, J., Groom, R., Herald, D., Lade, B., Mathers, S., Assafin, M., Camargo, J.I.B., Vieira-Martins, R., Andrei, A.H., da Silva Neto, D.N., Braga-Ribas, F., Behrend, R., 2011, "Constraints on Charon's Orbital Elements from the Double Stellar Occultation of 2008 June 22," The Astronomical Journal, 141, 67.
Pluto and its main satellite, Charon, occulted the same star on 2008 June 22. This event was observed from Australia and La Réion Island, providing the east and north Charon Plutocentric offset in the sky plane (J2000): X= + 12,070.5 ± 4 km (+ 546.2 ± 0.2 mas), Y= + 4,576.3 ± 24 km (+ 207.1 ± 1.1 mas) at 19:20:33.82 UT on Earth, corresponding to JD 2454640.129964 at Pluto. This yields Charon's true longitude L= 153.483 ± 0071 in the satellite orbital plane (counted from the ascending node on J2000 mean equator) and orbital radius r= 19,564 ± 14 km at that time. We compare this position to that predicted by (1) the orbital solution of Tholen & Buie (the "TB97" solution), (2) the PLU017 Charon ephemeris, and (3) the solution of Tholen et al. (the "T08" solution). We conclude that (1) our result rules out solution TB97, (2) our position agrees with PLU017, with differences of ΔL= + 0.073 ± 0071 in longitude, and Δr= + 0.6 ± 14 km in radius, and (3) while the difference with the T08 ephemeris amounts to only ΔL= 0.033 ± 0071 in longitude, it exhibits a significant radial discrepancy of Δr= 61.3 ± 14 km. We discuss this difference in terms of a possible image scale relative error of 3.35 ×nbsp;10.3in the 2002-2003 Hubble Space Telescope images upon which the T08 solution is mostly based. Rescaling the T08 Charon semi-major axis, a = 19, 570.45 km, to the TB97 value, a = 19636 km, all other orbital elements remaining the same ("T08/TB97" solution), we reconcile our position with the re-scaled solution by better than 12 km (or 0.55 mas) for Charon's position in its orbital plane, thus making T08/TB97 our preferred solution.
Singh, J., Begha, J.M., 2011, "Stability of equilibrium points in the generalized perturbed restricted three-body problem," Astrophysics and Space Science, 331, 511-519.
This paper studies the existence and stability of equilibrium points under the influence of small perturbations in the Coriolis and the centrifugal forces, together with the non-sphericity of the primaries. The problem is generalized in the sense that the bigger and smaller primaries are respectively triaxial and oblate spheroidal bodies. It is found that the locations of equilibrium points are affected by the non-sphericity of the bodies and the change in the centrifugal force. It is also seen that the triangular points are stable for 0< μ< μ c and unstable for μc≤μ <1/2, where μc is the critical mass parameter depending on the above perturbations, triaxiality and oblateness. It is further observed that collinear points remain unstable.
Stone, N., Loeb, A., 2011, "Prompt tidal disruption of stars as an electromagnetic signature of supermassive black hole coalescence," Monthly Notices of the Royal Astronomical Society, 224.
A precise electromagnetic measurement of the sky coordinates and redshift of a coalescing black hole binary holds the key for using its gravitational wave (GW) signal to constrain cosmological parameters and to test general relativity. Here we show that the merger of ~ 106-7 Mȯ black holes is generically followed by electromagnetic flares from tidally disrupted stars. The sudden recoil imparted to the merged black hole by GW emission promptly fills its loss cone and results in a tidal disruption rate of stars as high as ~ 0.1 yr-1. The prompt disruption of a single star within a galaxy provides a unique electromagnetic flag of a recent black hole coalescence event, and sequential disruptions could be used on their own to calibrate the expected rate of GW sources for pulsar timing arrays or the proposed Laser Interferometer Space Antenna.
Tanikawa, A., Umemura, M., 2011, "Successive Merger of Multiple Massive Black Holes in a Primordial Galaxy," The Astrophysical Journal, 728, L31.
Using highly accurate N-body simulations, we explore the evolution of multiple massive black holes (hereafter MBHs) in a primordial galaxy that is composed of stars and MBHs. The evolution is pursed with a fourth-order Hermite scheme, where not only three-body interaction of MBHs but also dynamical friction by stars are incorporated. Initially, 10 MBHs with equal masses of 107 M sun are set in a host galaxy with 1011 M sun. It is found that 4-6 MBHs merge successively within 1 Gyr, emitting gravitational wave radiation. The key process for the successive merger of MBHs is the dynamical friction by field stars, which enhances three-body interactions of MBHs when they enter the central regions of the galaxy. The heaviest MBH always composes a close binary at the galactic center, which shrinks owing to the angular momentum transfer by the third MBH and eventually merges. The angular momentum transfer by the third MBH is due to the sling-shot mechanism. We find that the secular Kozai mechanism does not work for a binary to merge if we include the relativistic pericenter shift. The simulations show that a multiple MBH system can produce a heavier MBH at the galactic center purely through N-body process. This merger path can be of great significance for the growth of MBHs in a primordial galaxy. The merger of multiple MBHs may be a potential source of gravitational waves for the Laser Interferometer Space Antenna and pulsar timing.
Taris, F., Souchay, J., Andrei, A.H., Bernard, M., Salabert, M., Bouquillon, S., Anton, S., Lambert, S.B., Gontier, A.-M., Barache, C., 2011, "Astrophotometric variability of CFHT-LS Deep 2 QSOs," Astronomy and Astrophysics, 526, 25.
Context. The current conventional realization of the ICRS (International Celestial Reference System) is, in the radio wavelength, the International Celestial Reference Frame 2 (ICRF2). The individual positions of the defining sources have been found to have accuracies better than 1 milliarcsecond (mas). In 2012, the European astrometric satellite Gaia will be launched. This mission will provide an astrometric catalog of an estimated number of 500 000 QSOs. The uncertainty in the coordinates is anticipated to be 200 microarcsecond (?as) for the magnitude = 20. If this were achieved, the ICRF and the Gaia related reference frame could be related with a ?as accuracy.
Aims: The goal of this work is both to measure the photometric variability of a set of quasars in a given field, and search wether this variability can be related to an astrometric instability characterized by a motion of the quasar photocenter. If this correlation existed for some given QSO, then it would be inadequate to materialize the Gaia extragalactic reference frame at the level of confidence required, i.e. the sub-milliarcsecond one. This should be an important result in the scope of the Gaia mission.
Methods: We use QSO CCD images obtained over 4.5 years with the Canada France Hawaïelescope (CFHT) in the framework of the CFHT-Legacy Survey (CFHT-LS). The pictures were analysed with both the SExtractor software and customised codes to perform a photometric calibration together with an astrometric one. A total of 41 QSOs in the Deep 2 field were analysed. Magnitude variations during more than 50 months are given at three different bandwiths G, R, and I. Among the set above, 5 quasars were chosen to test the ties between the postion of their centroid and their magnitude variations. For one of these 5 QSOs, the proximity of a neighbouring star allows the comparison between the PSFs.
Results: We clearly show significant photometric variations reaching sometimes more than one magnitude, for a good proportion of the 41 quasars in our sample. We show that these variations often occur within a few months, and that the correlation between the photometric curves in the three bands, G, R and I is obvious. As a second important result, we show that with a reasonably high probability, photometric variations for one quasar in our sample are accompagnied by substantial modification of its PSF. This paper is dedicated to the memory of Anne-Marie Gontier (1966-2010). A.-M. Gontier was an expert in the field of Earth rotation, reference systems and the modeling, analysis, and processing of VLBI observations for astrometric and geodetic applications.Figures 4-14 are only available in electronic form at http://www.aanda.org">http://www.aanda.org
Tinney, C.G., Butler, R.P., Jones, H.R.A., Wittenmyer, R.A., O'Toole, S., Bailey, J., Carter, B.D., 2011, "The Anglo-Australian Planet Search. XX. A Solitary Ice-giant Planet Orbiting HD 102365," The Astrophysical Journal, 727, 103.
We present 12 years of precision Doppler data for the very nearby G3 star HD 102365, which reveals the presence of a Neptune-like planet with a 16.0 M Earth minimum mass in a 122.1 day orbit. Very few "Super Earth" planets have been discovered to date in orbits this large and those that have been found reside in multiple systems of between three and six planets. HD 102365 b, in contrast, appears to orbit its star in splendid isolation. Analysis of the residuals to our Keplerian fit for HD 102365 b indicates that there are no other planets with minimum mass above 0.3 MJup orbiting within 5 AU and no other "Super Earths" more massive than 10 M Earth orbiting at periods shorter than 50 days. At periods of less than 20 days these limits drop to as low as 6 M Earth. There are now 32 exoplanets known with minimum mass below 20 M Earth, and interestingly the period distributions of these low-mass planets seem to be similar whether they orbit M-, K-, or G-type dwarfs. Based on observations obtained at the Anglo-Australian Telescope, Siding Spring, Australia.
van Saders, J.L., Gaudi, B.S., 2011, "Ensemble Analysis of Open Cluster Transit Surveys: Upper Limits on the Frequency of Short-period Planets Consistent with the Field," The Astrophysical Journal, 729, 63.
Several photometric surveys for short-period transiting giant planets have targeted a number of open clusters, but no convincing detections have been reported. Although each individual survey typically targeted an insufficient number of stars to expect a detection assuming the frequency of short-period giant planets found in surveys of field stars, we ask whether the lack of detections from the ensemble of open cluster surveys is inconsistent with expectations from the field planet population. We select a subset of existing transit surveys with well-defined selection criteria and quantified detection efficiencies, and statistically combine their null results to show that the upper limits on the planet fraction are 5.5% and 1.4% for 1.0 RJ and 1.5 RJ planets, respectively, in the 3 < P < 5 day period range. For the period range of 1 < P < 3 days, we find upper limits of 1.4% and 0.31% for 1.0 RJ and 1.5 RJ , respectively. Comparing these results to the frequency of short-period giant planets around field stars in both radial velocity and transit surveys, we conclude that there is no evidence to suggest that open clusters support a fundamentally different planet population than field stars, given the available data.
Veras, D., Ford, E.B., Payne, M.J., 2011, "Quantifying the Challenges of Detecting Unseen Planetary Companions with Transit Timing Variations," The Astrophysical Journal, 727, 74.
Both ground- and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. The variation in a planet's transit times may be used to infer the presence of additional planets. Deducing the masses and orbital parameters of such planets from transit time variations (TTVs) alone is a rich and increasingly relevant dynamical problem. In this work, we evaluate the extent of the degeneracies in this process, systematically explore the dependence of TTV signals on several parameters, and provide phase space plots that could aid observers in planning future observations. Our explorations are focused on a likely-to-be prevalent situation: a known transiting short-period Neptune- or Jupiter-sized planet and a suspected external low-mass perturber on a nearly coplanar orbit. Through ~107 N-body simulations, we demonstrate how TTV signal amplitudes may vary by orders of magnitude due to slight variations in any one orbital parameter (10-3 AU in a semimajor axis, 0.005 in eccentricity, or a few degrees in orbital angles), and quantify the number of consecutive transit observations necessary in order to obtain a reasonable opportunity of characterizing the unseen planet (>~50 observations). Planets in or near period commensurabilities of the form p:q, where p <= 20 and q <= 3, produce distinct TTV signatures, regardless of whether the planets are actually locked in a mean motion resonance. We distinguish these systems from the secular systems in our explorations. Additionally, we find that computing the autocorrelation function of a TTV signal can provide a useful diagnostic for identifying possible orbits for additional planets and suggest that this method could aid integration of TTV signals in future studies of particular exosystems.
Wahhaj, Z., Liu, M.C., Biller, B.A., Clarke, F., Nielsen, E.L., Close, L.M., Hayward, T.L., Mamajek, E.E., Cushing, M., Dupuy, T., Tecza, M., Thatte, N., Chun, M., Ftaclas, C., Hartung, M., Reid, I.N., Shkolnik, E.L., Alencar, S.H.P., Artymowicz, P., Boss, A., de Gouveia Dal Pino, E., Gregorio-Hetem, J., Ida, S., Kuchner, M., Lin, D.N.C., Toomey, D.W., 2011, "The Gemini NICI Planet-finding Campaign: Discovery of a Substellar L Dwarf Companion to the Nearby Young M Dwarf CD.35 2722," The Astrophysical Journal, 729, 139.
We present the discovery of a wide (67 AU) substellar companion to the nearby (21 pc) young solar-metallicity M1 dwarf CD.35 2722, a member of the ≈100 Myr AB Doradus association. Two epochs of astrometry from the NICI Planet-Finding Campaign confirm that CD.35 2722 B is physically associated with the primary star. Near-IR spectra indicate a spectral type of L4±1 with a moderately low surface gravity, making it one of the coolest young companions found to date. The absorption lines and near-IR continuum shape of CD.35 2722 B agree especially well the dusty field L4.5 dwarf 2MASS J22244381.0158521, while the near-IR colors and absolute magnitudes match those of the 5 Myr old L4 planetary-mass companion, 1RXS J160929.1.210524 b. Overall, CD.35 2722 B appears to be an intermediate-age benchmark for L dwarfs, with a less peaked H-band continuum than the youngest objects and near-IR absorption lines comparable to field objects. We fit Ames-Dusty model atmospheres to the near-IR spectra and find T eff= 1700-1900 K and log(g)= 4.5 ± 0.5. The spectra also show that the radial velocities of components A and B agree to within ±10 km s.1, further confirming their physical association. Using the age and bolometric luminosity of CD.35 2722 B, we derive a mass of 31 ± 8 M Jupfrom the Lyon/Dusty evolutionary models. Altogether, young late-M to mid-L type companions appear to be overluminous for their near-IR spectral type compared with field objects, in contrast to the underluminosity of young late-L and early-T dwarfs.
Wen, D.-H., Chen, W., 2011, "GEOPHYSICS, ASTRONOMY AND ASTROPHYSICS Properties of hyperon stars rotating at Keplerian frequency," Chinese Physics B, 20, 9701.
T he structure and properties of a Keplerian rotating hyperon star with an equation of state (EOS) investigated using the relativistic σ-ω-ρ model are examined by employing an accurate numerical scheme. It is shown that there is a clear rotating effect on the structure and properties, and that hyperon star matter cannot support a star with a mass larger than 1.9 M, even a star rotating at the fastest allowed frequency. The constraints of the two known fastest rotating frequencies (716 Hz and 1122 Hz) on the mass and radius of a hyperon star are also explored. Furthermore, our results indicate that the imprint of the rapid rotation of a hyperon star on the moment of inertia is clear; the backward equatorial redshift, the forward equatorial redshift and the polar redshift can be distinguished clearly, the forward equatorial redshift is always negative; and its figuration is far from a spherical symmetric shape.
Wen, Z.L., Jenet, F.A., Yardley, D., Hobbs, G.B., Manchester, R.N., 2011, "Constraining the Coalescence Rate of Supermassive Black-hole Binaries Using Pulsar Timing," The Astrophysical Journal, 730, 29.
Pulsar timing observations are used to place constraints on the rate of coalescence of supermassive black-hole (SMBH) binaries as a function of mass and redshift. In contrast to the indirect constraints obtained from other techniques, pulsar timing observations provide a direct constraint on the black-hole merger rate. This is possible since pulsar timing is sensitive to the gravitational waves (GWs) emitted by these sources in the final stages of their evolution. We find that upper bounds calculated from the recently published Parkes Pulsar Timing Array data are just above theoretical predictions for redshifts below 10. In the future, with improved timing precision and longer data spans, we show that a non-detection of GWs will rule out some of the available parameter space in a particular class of SMBH binary merger models. We also show that if we can time a set of pulsars to 10 ns timing accuracy, for example, using the proposed Square Kilometre Array, it should be possible to detect one or more individual SMBH binary systems.
Winn, J.N., Howard, A.W., Johnson, J.A., Marcy, G.W., Isaacson, H., Shporer, A., Bakos, G.Á, Hartman, J.D., Holman, M.J., Albrecht, S., Crepp, J.R., Morton, T.D., 2011, "Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-P-14b is Retrograde," The Astronomical Journal, 141, 63.
We present observations of the Rossiter-McLaughlin effect for two exoplanetary systems, revealing the orientations of their orbits relative to the rotation axes of their parent stars. HAT-P-4b is prograde, with a sky-projected spin-orbit angle of λ = -4.9 ± 11.9 deg. In contrast, HAT-P-14b is retrograde, with λ = 189.1 ± 5.1 deg. These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.
Wittenmyer, R.A., Tinney, C.G., O'Toole, S.J., Jones, H.R.A., Butler, R.P., Carter, B.D., Bailey, J., 2011, "On the Frequency of Jupiter Analogs," The Astrophysical Journal, 727, 102.
The Anglo-Australian Planet Search has now accumulated 12 years of radial-velocity data with long-term instrumental precision better than 3 m s-1. In this paper, we expand on earlier simulation work, to probe the frequency of near-circular, long-period gas-giant planets residing at orbital distances of 3-6 AU.the so-called Jupiter analogs. We present the first comprehensive analysis of the frequency of these objects based on radial-velocity data. We find that 3.3% of stars in our sample host Jupiter analogs; detailed, star-by-star simulations show that no more than 37% of stars host a giant planet between 3 and 6 AU.
Wouters, B., Riva, R.E.M., Lavallé D.A., Bamber, J.L., 2011, "Seasonal variations in sea level induced by continental water mass: First results from GRACE," Geophysical Research Letters, 38, 03303.
Variations in the Earth's water cycle are commonly quantified by their effect on global mean sea-level. However, the interaction between passive adjustment of the ocean to changes in gravitational attraction due to mass redistribution, the related deformation of the solid Earth and disturbances in the Earth's rotation vector will yield a distribution that is more complicated than a uniform rise or fall of the ocean's surface. In this study, we present the first estimates of seasonal changes in passive sea-level (which we define as the height difference between the sea surface at rest and ocean floor, excluding steric and dynamical effects) based on direct observations of surface mass redistribution, made by the Gravity Recovery and Climate Experiment (GRACE) between 2003 and 2010. We show that this .selfgravitation-effect. causes seasonal variations of the sea-level of up to 1 cm - comparable to the amplitude of the long-period tides - and that inclusion in numerical ocean models results in a better agreement between observed and modelled ocean bottom pressure variations, particularly in coastal zones.
Wright, D.J., ChenéA.-N., De Cat, P., Marois, C., Mathias, P., Macintosh, B., Isaacs, J., Lehmann, H., Hartmann, M., 2011, "Determination of the Inclination of the Multi-planet Hosting Star HR 8799 Using Asteroseismology," The Astrophysical Journal, 728, L20.
Direct imaging of the HR 8799 system was a major achievement in the study of exoplanets. HR 8799 is a γ Doradus variable and asteroseismology can provide an independent constraint on the inclination. Using 650 high signal-to-noise, high-resolution, full visual wavelength spectroscopic observations obtained over two weeks at Observatoire de Haute Provence with the SOPHIE spectrograph, we find that the main frequency in the radial velocity data is 1.9875 day-1. This frequency corresponds to the main frequency as found in previous photometric observations. Using the FAMIAS software to identify the pulsation modes, we find that this frequency is a prograde = 1 sectoral mode and obtain the constraint that inclination i >~ 40°.
Zeng, X.-X., Li, L., 2011, "Geophysics, Astronomy, and Astrophysics Hawking Tunneling Radiation of Black Holes in Deformed H ŏrava.Lifshitz Gravity," Communications in Theoretical Physics, 55, 376-380.
Tunneling of scalar particles and Dirac particles from a black hole in the deformed Hŏrava.Lifshitz gravity is discussed in this paper. We consider the case that the dynamical coupling constant λ = 1, when it reduces to Einstein's General Relativity at large scales and the black hole behaves like the Reissner.Nordströlack hole. The result shows that though the black hole entropy bears logarithmic correction, the tunneling probability is still related to its differences for the scalar particles and Dirac particles.