Andrews, S.M., Wilner, D.J., Espaillat, C., Hughes, A.M., Dullemond, C.P., McClure, M.K., Qi, C., Brown, J.M., 2011, "Resolved Images of Large Cavities in Protoplanetary Transition Disks," The Astrophysical Journal, 732, 42.

 

       We present new and archival high angular resolution Submillimeter Array (SMA) observations of the 880 micron dust continuum emission from 12 transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted cavity around the central star. Using two-dimensional Monte Carlo radiative transfer calculations, we interrpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA continuum visibilities and spectral energy distributions. The cavities in these disks are large (R = 15-73 AU) and substantially depleted of small (micron-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are common among the millimeter-bright disk population, comprising at least 20% of the disks in the bright half of the millimeter luminosity distribution. We suggest that these observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions - young brown dwarfs of giant planets on long-period orbits.

 

 

Avsyuk, Y.N., Maslov, L.A., 2011, "Long Period Tidal Force Variations and Regularities in Orbital Motion of the Earth-Moon Binary Planet System," Earth Moon and Planets, 108, 77-85.

 

       We have studied long period, 206 and 412 day, variations in tidal sea level corresponding to various moon phases collected from five observatories in the Northern and Southern hemispheres. Variations in sea level in the Bay of Fundy, on the eastern Canadian seaboard, with periods of variation 206 days, and 412 days, have been discovered and carefully studied by Desplanque and Mossman (Proceedings of the 4th Bay of Fundy workshop Saint John, New Brunswick. The current manuscript focuses on analyzing a larger volume of observational sea level tide data as well as on rigorous mathematical analysis of tidal force variations in the Sun-Earth-Moon system. We have developed a twofold model, both conceptual and mathematical, of astronomical cycles in the Sun-Earth-Moon system to explain the observed periodicity. Based on an analytical solution of the tidal force variation in the Sun-Earth-Moon system, it is shown that the tidal force can be decomposed into two components: the Keplerian component and the Perturbed component. The Perturbed component of the tidal force variation was calculated, and it was shown that the observed periodicity, 206 and 412 days, of atmospheric and hydrosphere tides results from variations of the Perturbed component of tidal force. The amplitude of the perturbed component of tidal force is 19 ×10-8 N/kg. It is the same order of magnitude as the amplitude of the Keplerian component of tidal force: 58 ×10-8 N/kg. It follows that the perturbed component of the variation of a tidal force must always be taken into consideration along with the Keplerian component in geodynamical constructions involving tides.

 

 

Baer, J., Chesley, S.R., Matson, R.D., 2011, "Astrometric Masses of 26 Asteroids and Observations on Asteroid Porosity," The Astronomical Journal, 141, 143.

 

       As an application of our recent observational error model, we present the astrometric masses of 26 main-belt asteroids. We also present an integrated ephemeris of 300 large asteroids, which was used in the mass determination algorithm to model significant perturbations from the rest of the main belt. After combining our mass estimates with those of other authors, we study the bulk porosities of over 50 main-belt asteroids and observe that asteroids as large as 300 km in diameter may be loose aggregates. This finding may place specific constraints on models of main-belt collisional evolution. Additionally, we observe that C-group asteroids tend to have significantly higher macroporosity than S-group asteroids.

 

 

Baland, R.-M., van Hoolst, T., Yseboodt, M., Karatekin, Ö, 2011, "Titan's obliquity as evidence of a subsurface ocean?," Astronomy and Astrophysics, 530, 141.

 

       On the basis of gravity and radar observations with the Cassini spacecraft, the moment of inertia of Titan and the orientation of Titan's rotation axis have been estimated in recent studies. According to the observed orientation, Titan is close to the Cassini state. However, the observed obliquity is inconsistent with the estimate of the moment of inertia for an entirely solid Titan occupying the Cassini state. We propose a new Cassini state model for Titan in which we assume the presence of a liquid water ocean beneath an ice shell and consider the gravitational and pressure torques arising between the different layers of the satellite. With the new model, we find a closer agreement between the moment of inertia and the rotation state than for the solid case, strengthening the possibility that Titan has a subsurface ocean.

 

 

Barker, A.J., 2011, "Three-dimensional simulations of internal wave breaking and the fate of planets around solar-type stars," Monthly Notices of the Royal Astronomical Society, 414, 1365-1378.

 

       We study the fate of internal gravity waves approaching the centre of an initially non-rotating solar-type star, by performing three-dimensional numerical simulations using a Boussinesq-type model. These waves are excited at the top of the radiation zone by the tidal forcing of a short-period planet on a circular, coplanar orbit. This extends previous work done in two dimensions by Barker & Ogilvie. We first derive a linear wave solution, which is not exact in three dimensions; however, the reflection of ingoing waves from the centre is close to perfect for moderate amplitude waves. Waves with sufficient amplitude to cause isentropic overturning break, and deposit their angular momentum near the centre. This forms a critical layer, at which the angular velocity of the flow matches the orbital angular frequency of the planet. This efficiently absorbs ingoing waves, and spins up the star from the inside out, while the planet spirals into the star.

 

We also perform numerical integrations to determine the linearized adiabatic tidal response throughout the star, in a wide range of solar-type stellar models with masses in the range 0.5 ≤m★/Mȯ≤ 1.1, throughout their main-sequence lifetimes. The aim is to study the influence of the launching region for these waves at the top of the radiation zone in more detail, and to determine the accuracy of a semi-analytic approximation for the tidal torque on the star, which was derived under the assumption that all ingoing wave angular momentum is absorbed in a critical layer.

 

The main conclusion of this work is that this non-linear mechanism of tidal dissipation could provide an explanation for the survival of all short-period extrasolar planets observed around FGK stars, while it predicts the destruction of more massive planets. This work provides further support for the model outlined in a previous paper by Barker & Ogilvie, and makes predictions that will be tested by ongoing observational studies, such as WASP and Kepler.

 

 

Barzilay, Y., 2011, "Full Simulation of the Open Field Lines Above a Pulsar's Polar Cap. I. Acceleration," The Astrophysical Journal, 732, 123.

 

       We have programmed a full simulation of the open field lines above the polar cap of a magnetized pulsar using a time-dependent, particle-in-cell (PIC) numerical code. We consider the case of free ejection of electrons from the star surface, a space charge limited flow (SCLF) model. We report here the first results of the simulation. Electrons are accelerating along the open field lines according to the flat spacetime SCLF Lorentz-factor prediction, with an oscillation pattern. Then, we add the General Relativistic (GR) frame-dragging correction that provides the particles the high Lorentz factor (106-107) needed to initiate pair production. The electrons accelerate according to the GR Lorentz-factor prediction, with an oscillation pattern. Electron-positron pair production is now being programmed using cross-sections from the literature and the Monte Carlo code. After completing this stage, we will automatically get (1) the positron return current (thus, we can calculate polar cap heating and X-ray emission), (2) the photons' and electrons' observed spectra (photons and electrons that escape the magnetosphere after the cascade), (3) the pulsar death line (pulsars without enough pair production), (4) the PFF height (pair formation front location), and (5) the multiplicity (number of pairs produced per primary particle). Those results will be reported in a different paper.

 

 

Bear, E., Soker, N., Harpaz, A., 2011, "Possible Implications of the Planet Orbiting the Red Horizontal Branch Star HIP 13044," The Astrophysical Journal, 733, L44.

 

       We propose a scenario to account for the surprising orbital properties of the planet orbiting the metal-poor red horizontal branch star HIP 13044. The orbital period of 16.2 days implies that the planet went through a common envelope phase inside the red giant branch (RGB) stellar progenitor of HIP 13044. The present properties of the star imply that it maintained a substantial envelope mass of 0.3 M sun, raising the question of how the planet survived the common envelope before the envelope itself was lost? If such a planet enters the envelope of an RGB star, it is expected to spiral-in to the very inner region within <~ 100 yr, and be evaporated or destroyed by the core. We speculate that the planet was engulfed by the star as a result of the core helium flash that caused this metal-poor star to swell by a factor of ~3-4. The evolution following the core helium flash is very rapid, and some of the envelope is lost due to the interaction with the planet, and the rest of the envelope shrinks within about a hundred years. This is about equal to the spiraling-in time, and the planet survived.

 

 

Bé, B., Bakos, G.Á, Hartman, J., Torres, G., Latham, D.W., Jordá A., Arriagada, P., Bayliss, D., Kiss, L.L., Ková, G., Quinn, S.N., Marcy, G.W., Howard, A.W., Fischer, D.A., Johnson, J.A., Esquerdo, G.A., Noyes, R.W., Buchhave, L.A., Sasselov, D.D., Stefanik, R.P., Perumpilly, G., Lár, J., Papp, I., Sá, P., 2011, "HAT-P-27b: A Hot Jupiter Transiting a G Star on a 3 Day Orbit," The Astrophysical Journal, 734, 109.

 

       We report the discovery of HAT-P-27b, an exoplanet transiting the moderately bright G8 dwarf star GSC 0333-00351 (V = 12.214). The orbital period is 3.039586 ± 0.000012 days, the reference epoch of transit is 2455186.01879 ± 0.00054 (BJD), and the transit duration is 0.0705 ± 0.0019 days. The host star with its effective temperature 5300 ± 90 K is somewhat cooler than the Sun and is more metal-rich with a metallicity of +0.29 ± 0.10. Its mass is 0.94 ± 0.04 M sun and radius is 0.90+0.05 - 0.04 R sun. For the planetary companion we determine a mass of 0.660 ± 0.033 M J and radius of 1.038+0.077 - 0.058 R J. For the 30 known transiting exoplanets between 0.3 M J and 0.8 M J, a negative correlation between host star metallicity and planetary radius and an additional dependence of planetary radius on equilibrium temperature are confirmed at a high level of statistical significance.

 

Beust, H., Bonneau, D., Mourard, D., Lafrasse, S., Mella, G., Duvert, G., Chelli, A., 2011, "On the use of the Virtual Observatory to select calibrators for phase-referenced astrometry of exoplanet-host stars," Monthly Notices of the Royal Astronomical Society, 414, 108-115.

 

       Phase-referenced interferometric astrometry offers the possibility to look for exoplanets around bright stars. Instruments like PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry) will measure the astrometric wobble of a candidate star due to an exoplanet relative to a close-by 'calibrator' star, located within the instrument's observing field (1 arcmin in the PRIMA case). Stars with already known exoplanets will constitute the first targets for this technique, as it will provide a way to further specify the characteristics of the known exoplanets, such as the inclinations. The main requirement is to have a calibrator in the vicinity of the star. We provide here a list of calibrators for all stars with known exoplanets obtained using data mining and Virtual Observatory techniques. This list is available online and revised regularly. The calibrators are found from catalogues available at Centre de Donné astronomiques de Strasbourg (CDS) using the SEARCHCAL software developed at Jean-Marie Mariotti Center (JMMC). In our test case, the calibrators are found within 1 arcmin angular distance for approximately 50 per cent of the stars tested, and often closer. They are all faint objects from the Two Micron All Sky Survey (2MASS) with K magnitudes between 13 and 15. A list of the most promising targets is also given.

 

 

Bhattacharyya, S., 2011, "Ways to constrain neutron star equation of state models using relativistic disc lines," Monthly Notices of the Royal Astronomical Society, 844.

 

       Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular orbit (ISCO). Therefore an inferred disc inner edge radius either provides the stellar radius, or can directly constrain stellar equation of state (EoS) models using the theoretically computed ISCO radius for the space-time of a rapidly spinning neutron star. However, this procedure requires numerical computation of stellar and ISCO radii for various EoS models and neutron star configurations using an appropriate rapidly spinning stellar space-time. We have fully general relativistically calculated about 16 000 stable neutron star structures to explore and establish the above mentioned procedure, and to show that the Kerr space-time is inadequate for this purpose. Our work systematically studies the methods to constrain EoS models using relativistic disc lines, and will motivate future X-ray astronomy instruments.

 

 

Boardman, J.W., Pieters, C.M., Green, R.O., Lundeen, S.R., Varanasi, P., Nettles, J., Petro, N., Isaacson, P., Besse, S., Taylor, L.A., 2011, "Measuring moonlight: An overview of the spatial properties, lunar coverage, selenolocation, and related Level 1B products of the Moon Mineralogy Mapper," Journal of Geophysical Research (Planets), 116

      

The Moon Mineralogy Mapper (M3), a high-resolution, high-precision imaging spectrometer, flew on board India's Chandrayaan-1 Mission from October 2008 through August 2009. This paper describes some of the spatial sampling aspects of the instrument, the planned mission, and the mission as flown. We also outline the content and context of the resulting Level 1B spatial products that form part of the M3 archive. While designed and planned to operate for 2 years in a 100 km lunar orbit, M3 was able to meet its lunar coverage requirements despite the shortened mission; an increase of the orbit altitude to 200 km; and several relevant problems with spacecraft attitude, timing, and ephemeris. The unexpected spacecraft issues required us to invent a novel two-step approach for selenolocation. Leveraging newly available Lunar Reconnaissance Orbiter-Lunar Orbiter Laser Altimeter (LOLA) topography and an improved spacecraft ephemeris, we have created a method that permits us to bootstrap spacecraft attitude estimates from the image data themselves. This process performs a nonlinear optimization to honor a set of data-derived image-to-image tie points and image-to-LOLA control points. Error analysis of the final results suggests we have converged to a selenolocation result that has image-to-image root-mean-square (RMS) errors less than 200 m and image-to-LOLA RMS errors less than 450 m, despite using data-derived spacecraft attitude results. The Level 1B products include the lunar coordinates resulting from this inversion process and 10 relevant observational geometry parameters that fully characterize the ray tracing geometry on a pixel-by-pixel basis.

 

 

Bonsor, A., Mustill, A.J., Wyatt, M.C., 2011, "Dynamical effects of stellar mass-loss on a Kuiper-like belt," Monthly Notices of the Royal Astronomical Society, 414, 930-939.

 

       A quarter of DA white dwarfs are metal polluted, yet elements heavier than helium sink down through the stellar atmosphere on time-scales of days. Hence, these white dwarfs must be the currently accreting material containing heavy elements. Here we consider whether the scattering of comets or asteroids from an outer planetary system, following stellar mass-loss on the asymptotic giant branch, can reproduce these observations. We use N-body simulations to investigate the effects of stellar mass-loss on a simple system consisting of a planetesimal belt whose inner edge is truncated by a planet. Our simulations find that, starting with a planetesimal belt population fitted to the observed main-sequence evolution, sufficient mass is scattered into the inner planetary system to explain the inferred heavy element accretion rates. This assumes that a fraction of the mass scattered into the inner planetary system ends up on star-grazing orbits, is tidally disrupted and is accreted on to the white dwarf. The simulations also reproduce the observed decrease in accretion rate with cooling age and predict accretion rates in old (>1 Gyr) white dwarfs, in line with observations. The efficiency we assumed for material scattered into the inner planetary system to end up on star-grazing orbits is based on a solar-like planetary system, since the simulations show that a single planet is not sufficient. Although the correct level of accretion is reproduced, the simulations predict a higher fraction of accreting white dwarfs than observed. This could indicate that the evolved planetary systems are less efficient in scattering bodies on to star-grazing orbits or that dynamical instabilities post-stellar mass-loss cause rapid planetesimal belt depletion for a significant fraction of systems.

 

 

Brown, D.J.A., Collier Cameron, A., Hall, C., Hebb, L., Smalley, B., 2011, "Are falling planets spinning up their host stars?," Monthly Notices of the Royal Astronomical Society, 633.

 

       We investigate the effects of tidal interactions on the planetary orbits and stellar spin rates of the WASP-18 and WASP-19 planetary systems using a forward integration scheme. By fitting the resulting evolutionary tracks to the observed eccentricity, semimajor axis and stellar rotation rate, and to the stellar age derived from isochronal fitting, we are able to place constraints on the stellar and planetary reduced tidal quality factors, Q's and Q'p. We find that for WASP-18, log (Q's) = 8.21+0.90-0.52 and log (Q'p) = 7.77+1.54-1.25, implying a system age of 0.579+0.305-0.250 Gyr. For WASP-19 we obtain values of log (Q's) = 6.47+2.19-0.95 and log (Q'p) = 6.75+1.86-1.77, suggesting a system age of 1.60+2.84-0.79 Gyr and a remaining lifetime of 0.0067+1.1073-0.0061 Gyr. We investigate a range of evolutionary histories consistent with these results and the observed parameters for both systems, and find that the majority imply that the stars have been spun up through tidal interactions as the planets spiral towards their Roche limits. We examine a variety of evidence for WASP-19 A.s age, both for the value above and for a younger age consistent with gyrochronology, and conclude that the older estimate is more likely to be correct. This suggests that WASP-19 b might be in the final stages of the spiral-in process, although we are unable to rule out the possibility that it has a substantial remaining lifetime.

 

 

Brown, R.A., 2011, "Density Estimation for Projected Exoplanet Quantities," The Astrophysical Journal, 733, 68.

 

       Exoplanet searches using radial velocity (RV) and microlensing (ML) produce samples of "projected" mass and orbital radius, respectively. We present a new method for estimating the probability density distribution (density) of the unprojected quantity from such samples. For a sample of n data values, the method involves solving n simultaneous linear equations to determine the weights of delta functions for the raw, unsmoothed density of the unprojected quantity that cause the associated cumulative distribution function (CDF) of the projected quantity to exactly reproduce the empirical CDF of the sample at the locations of the n data values. We smooth the raw density using nonparametric kernel density estimation with a normal kernel of bandwidth σ. We calibrate the dependence of σ on n by Monte Carlo experiments performed on samples drawn from a theoretical density, in which the integrated square error is minimized. We scale this calibration to the ranges of real RV samples using the Normal Reference Rule. The resolution and amplitude accuracy of the estimated density improve with n. For typical RV and ML samples, we expect the fractional noise at the PDF peak to be approximately 80 n -log 2. For illustrations, we apply the new method to 67 RV values given a similar treatment by Jorissen et al. in 2001, and to the 308 RV values listed at exoplanets.org on 2010 October 20. In addition to analyzing observational results, our methods can be used to develop measurement requirements.particularly on the minimum sample size n.for future programs, such as the microlensing survey of Earth-like exoplanets recommended by the Astro 2010 committee.

 

Bro., M., Rozehnal, J., 2011, "Eurybates - the only asteroid family among Trojans?," Monthly Notices of the Royal Astronomical Society, 414, 565-574.

 

       We study the orbital and physical properties of Trojan asteroids of Jupiter. We try to discern all the families previously discussed in the literature, but we conclude that there is only one significant family among the Trojans, namely the cluster around the asteroid (3548) Eurybates. This is the only cluster that has all of the following characteristics: (i) it is clearly concentrated in the proper-element space; (ii) the size-frequency distribution is different from that of background asteroids; (iii) we have a reasonable collisional/dynamical model of the family. Henceforth, we can consider it as a real collisional family. We also report the discovery of a possible family around the asteroid (4709) Ennomos, composed mostly of small asteroids. The asteroid (4709) Ennomos is known to have a very high albedo pV ≃ 0.15, which may be related to the hypothetical cratering event that exposed ice. The relation between the collisional family and the exposed surface of the parent body offers a unique means to study the physics of cratering events. However, more data are needed to confirm the existence of this family and its relationship with Ennomos.

 

 

Buchhave, L.A., Bakos, G.Á, Hartman, J.D., Torres, G., Latham, D.W., Andersen, J., Ková, G., Noyes, R.W., Shporer, A., Esquerdo, G.A., Fischer, D.A., Johnson, J.A., Marcy, G.W., Howard, A.W., Bé, B., Sasselov, D.D., F?ré, G., Quinn, S.N., Stefanik, R.P., Szklená T., Berlind, P., Calkins, M.L., Lár, J., Papp, I., Sá, P., 2011, "Hat-P-28b and Hat-P-29b: Two Sub-Jupiter Mass Transiting Planets," The Astrophysical Journal, 733, 116.

 

       We present the discovery of two transiting exoplanets. HAT-P-28b orbits a V = 13.03 G3 dwarf star with a period P = 3.2572 days and has a mass of 0.63 ± 0.04 M J and a radius of 1.21+0.11 - 0.08 R J yielding a mean density of 0.44 ± 0.09 g cm-3. HAT-P-29b orbits a V = 11.90 F8 dwarf star with a period P = 5.7232 days and has a mass of 0.78+0.08 - 0.04 M J and a radius of 1.11+0.14 - 0.08 R J yielding a mean density of 0.71 ± 0.18 g cm-3. We discuss the properties of these planets in the context of other known transiting planets.

 

 

Chan, T., Ingemyr, M., Winn, J.N., Holman, M.J., Sanchis-Ojeda, R., Esquerdo, G., Everett, M., 2011, "The Transit Light-curve Project. XIV. Confirmation of Anomalous Radii for the Exoplanets TrES-4b, HAT-P-3b, and WASP-12b," The Astronomical Journal, 141, 179.

 

       We present transit photometry of three exoplanets, TrES-4b, HAT-P-3b, and WASP-12b, allowing for refined estimates of the systems' parameters. TrES-4b and WASP-12b were confirmed to be "bloated" planets, with radii of 1.706 ± 0.056R Jup and 1.736 ± 0.092R Jup, respectively. These planets are too large to be explained with standard models of gas giant planets. In contrast, HAT-P-3b has a radius of 0.827 ± 0.055R Jup, smaller than a pure hydrogen-helium planet and indicative of a highly metal-enriched composition. Analyses of the transit timings revealed no significant departures from strict periodicity. For TrES-4, our relatively recent observations allow for improvement in the orbital ephemerides, which is useful for planning future observations.

 

 

Cornish, N.J., 2011, "Detection strategies for extreme mass ratio inspirals," Classical and Quantum Gravity, 28, 4016.

 

       The capture of compact stellar remnants by galactic black holes provides a unique laboratory for exploring the near-horizon geometry of the Kerr spacetime, or possible departures from general relativity if the central cores prove not to be black holes. The gravitational radiation produced by these extreme mass ratio inspirals (EMRIs) encodes a detailed map of the black hole geometry, and the detection and characterization of these signals is a major scientific goal for the LISA mission. The waveforms produced are very complex, and the signals need to be coherently tracked for tens of thousands of cycles to produce a detection, making EMRI signals one of the most challenging data analysis problems in all of gravitational wave astronomy. Estimates for the number of templates required to perform an exhaustive grid-based matched-filter search for these signals are astronomically large, and far out of reach of current computational resources. Here I describe an alternative approach that employs a hybrid between genetic algorithms and Markov chain Monte Carlo techniques, along with several time-saving techniques for computing the likelihood function. This approach has proven effective at the blind extraction of relatively weak EMRI signals from simulated LISA data sets.

 

 

Crepp, J.R., Johnson, J.A., 2011, "Estimates of the Planet Yield from Ground-based High-contrast Imaging Observations as a Function of Stellar Mass," The Astrophysical Journal, 733, 126.

 

       We use Monte Carlo simulations to estimate the number of extrasolar planets that are directly detectable in the solar neighborhood using current and forthcoming high-contrast imaging instruments. Our calculations take into consideration the important factors that govern the likelihood for imaging a planet, including the statistical properties of stars in the solar neighborhood, correlations between star and planet properties, observational effects, and selection criteria. We consider several different ground-based surveys, both biased and unbiased, and express the resulting planet yields as a function of stellar mass. Selecting targets based on their youth and visual brightness, we find that strong correlations between star mass and planet properties are required to reproduce high-contrast imaging results to date (i.e., HR 8799, ? Pic). Using the most recent empirical findings for the occurrence rate of gas-giant planets from radial velocity (RV) surveys, our simulations indicate that naive extrapolation of the Doppler planet population to semimajor axes accessible to high-contrast instruments provides an excellent agreement between simulations and observations using present-day contrast levels. In addition to being intrinsically young and sufficiently bright to serve as their own beacon for adaptive optics correction, A-stars have a high planet occurrence rate and propensity to form massive planets in wide orbits, making them ideal targets. The same effects responsible for creating a multitude of detectable planets around massive stars conspire to reduce the number orbiting low-mass stars. However, in the case of a young stellar cluster, where targets are approximately the same age and situated at roughly the same distance, MK-stars can easily dominate the number of detections because of an observational bias related to small number statistics. The degree to which low-mass stars produce the most planet detections in this special case depends upon whether multiple formation mechanisms are at work. Upon relaxing our assumption that planets in ultra-wide (a > 100 AU) orbits resemble the RV sample, our simulations suggest that the companions found orbiting late-type stars (AB Pic, 1RXSJ1609, GSC 06214, etc.) are consistent with a formation channel distinct from that of RV planets. These calculations explain why planets have thus far been imaged preferentially around A-stars and K-, M-stars, but no spectral types in between, despite concerted efforts targeting F-, G-stars.

 

 

Deng, X., Finn, L.S., 2011, "Pulsar timing array observations of gravitational wave source timing parallax," Monthly Notices of the Royal Astronomical Society, 414, 50-58.

 

       Pulsar timing arrays (PTAs) act to detect gravitational waves by observing the small, correlated effect the waves have on pulse arrival times at the Earth. This effect has conventionally been evaluated assuming the gravitational wave phase fronts are planar across the array, an assumption that is valid only for sources at distances R≫ 2πL2/λ, where L is physical extent of the array and λ is the radiation wavelength. In the case of PTAs, the array size is of the order of the pulsar-Earth distance (kpc) and λ is of the order of parsec. Correspondingly, for point gravitational wave sources closer than .100 Mpc, the PTA response is sensitive to the source parallax across the pulsar-Earth baseline. Here, we evaluate the PTA response to gravitational wave point sources including the important wavefront curvature effects. Taking the wavefront curvature into account, the relative amplitude and phase of the timing residuals associated with a collection of pulsars allow us to measure the distance to, and the sky position of, the source.

 

 

Donnison, J.R., 2011, "The Hill stability of binary asteroid and binary Kuiper Belt systems," Monthly Notices of the Royal Astronomical Society, 699.

 

       The dynamical stability of a bound triple system composed of a binary asteroid system or Kuiper Belt binary system moving on an orbit inclined to a central third body, the Sun, is discussed in terms of Hill stability for the full three-body problem. The regions of Hill stability of these triple systems, where the binary mass is very small compared with that of the third body, can be determined against the possibility of disruption, component exchange and capture. The critical Hill stability curves for the binary mass range of these types of systems are determined for different secondary-to-primary mass ratios as a function of their orbital eccentricity. The regions of stability are found to increase with increasing binary mass. The regions, however, decrease in size substantially with increasing orbital eccentricity and also decrease slightly as the secondary/primary mass ratio of the binary is decreased.

 

The currently observed binary and multiple asteroid systems are discussed generally. In the majority of systems, the primary component is very much larger than the secondary component, forming an asteroid-satellite system. It was found that those systems where the binary mass is well determined would lie in stable regions if they moved on circular orbits, but when their eccentricity is taken into account, it is less clear that the systems are stable. The same is likely to be true for the systems where the masses are not well established. Upper mass limits could be placed on these systems that would ensure they are Hill stable. The currently observed Kuiper Belt binaries were also discussed generally. The majority of these binary systems have secondary components which are often comparable to the diameter of the primary component forming a true binary system. Similar to the asteroid binaries, it was found that binary systems where the mass was well determined were stable if they moved on circular orbits relative to the Sun. When the eccentricity is taken into account, it is less clear that the systems are stable. The same conclusions are also likely to be true for the systems with unknown masses. Upper mass limits again can be placed on these systems that would ensure they are Hill stable.

 

 

Emelyanov, N.V., Andreev, M.V., Berezhnoi, A.A., Bekhteva, A.S., Vashkovyak, S.N., Velikodskii, Y.I., Vereshchagina, I.A., Gorshanov, D.L., Devyatkin, A.V., Izmailov, I.S., Ivanov, A.V., Irsmambetova, T.R., Kozlov, V.A., Karashevich, S.V., Kurenya, A.N., Naiden, Y.V., Naumov, K.N., Parakhin, N.A., Raskhozhev, V.N., Selyaev, S.A., Sergeev, A.V., Sokov, E.N., Khovrichev, M.Y., Khrutskaya, E.V., Chernikov, M.M., 2011, "Astrometric results of observations at Russian observatories of mutual occultations and eclipses of Jupiter's Galilean satellites in 2009," Solar System Research, 45, 264-277.

 

       In 2009, in five Russian observatories photometric observations of Jupiter's Galilean satellites during their mutual occultations and eclipses were carried out. Based on these observations, an original method was used to ascertain astrometric results such as the difference between the coordinates of pairs of satellites. Fifty-three phenomena were successfully observed. A total of 94 light curves of satellites were measured. The error in the coordinates of satellites due to random errors in photometry, calculated on all data obtained, was 0.041″ in right ascension and 0.046″ in declination. The discrepancies between the theory and observations in these coordinates was found to be 0.060″ and 0.057″, respectively. The results were uploaded to the common database for all observations of natural satellites of planets at the Natural Satellites Data Center (NSDC), which is available online at http://www.sai.msu.ru/neb/nss/index.htm. For the first time in the practice of photometric observations of satellites in epochs of mutual occultations and eclipses a new method of observation was tested, which eliminates from astrometric results the major systematic errors caused by an inaccurate account of the background level. The tests were conducted in the Terskol Observatory and the observatory of the Crimean laboratory of the Sternberg State Astronomical Institute of the Moscow State University. The application of the new method showed that the elimination of the background level at these observatories was carried out correctly.

 

Escapa, A., 2011, "Corrections stemming from the non-osculating character of the Andoyer variables used in the description of rotation of the elastic Earth," Celestial Mechanics and Dynamical Astronomy, 110, 99-142.

 

       We explore the evolution of the angular velocity of an elastic Earth model, within the Hamiltonian formalism. The evolution of the rotation state of the Earth is caused by the tidal deformation exerted by the Moon and the Sun. It can be demonstrated that the tidal perturbation to spin depends not only upon the instantaneous orientation of the Earth, but also upon its instantaneous angular velocity. Parameterizing the orientation of the Earth figure axis with the three Euler angles, and introducing the canonical momenta conjugated to these, one can then show that the tidal perturbation depends both upon the angles and the momenta. This circumstance complicates the integration of the rotational motion. Specifically, when the integration is carried out in terms of the canonical Andoyer variables (which are the rotational analogues to the orbital Delaunay variables), one should keep in mind the following subtlety: under the said kind of perturbations, the functional dependence of the angular velocity upon the Andoyer elements differs from the unperturbed dependence (Efroimsky in Proceedings of Journé 2004: Systès de rérence spatio-temporels. l'Observatoire de Paris, pp 74-81) This happens because, under angular velocity dependent perturbations, the requirement for the Andoyer elements to be canonical comes into a contradiction with the requirement for these elements to be osculating, a situation that parallels a similar antinomy in orbital dynamics. Under the said perturbations, the expression for the angular velocity acquires an additional contribution, the so called convective term. Hence, the time variation induced on the angular velocity by the tidal deformation contains two parts. The first one comes from the direct terms, caused by the action of the elastic perturbation on the torque-free expressions of the angular velocity. The second one arises from the convective terms. We compute the variations of the angular velocity through the approach developed in Getino and Ferráiz (Celest. Mech. Dyn. Astron. 61:117-180), but considering the contribution of the convective terms. Specifically, we derive analytical formulas that determine the elastic perturbations of the directional angles of the angular velocity with respect to a non-rotating reference system, and also of its Cartesian components relative to the Tisserand reference system of the Earth. The perturbation of the directional angles of the angular velocity turns out to be different from the evolution law found in Kubo (Celest. Mech. Dyn. Astron. 105:261-274), where it was stated that the evolution of the angular velocity vector mimics that of the figure axis. We investigate comprehensively the source of this discrepancy, concluding that the difference between our results and those obtained in Ibid. stems from an oversimplification made by Kubo when computing the direct terms. Namely, in his computations Kubo disregarded the motion of the tide raising bodies with respect to a non-rotating reference system when compared with the Earth rotational motion. We demonstrate that, from a numerical perspective, the convective part provides the principal contribution to the variation of the directional angles and of length of day. In the case of the x and y components in the Tisserand system, the convective contribution is of the same order of magnitude as the direct one. Finally, we show that the approximation employed in Kubo ( Ibid.) leads to significant numerical differences at the level of a hundred micro-arcsecond.

 

 

Greenberg, R., Van Laerhoven, C., 2011, "Tidal Evolution of a Secularly Interacting Planetary System," The Astrophysical Journal, 733, 8.

 

       In a multi-planet system, a gradual change in one planet's semimajor axis will affect the eccentricities of all the planets, as angular momentum is distributed via secular interactions. If tidal dissipation in the planet is the cause of the change in semimajor axis, it also damps that planet's eccentricity, which in turn also contributes to the evolution of all the eccentricities. Formulae quantifying the combined effects on the whole system due to semimajor axis changes, as well as eccentricity damping, are derived here for a two-planet system. The CoRoT 7 system is considered as an example.

 

 

Guillochon, J., Ramirez-Ruiz, E., Lin, D., 2011, "Consequences of the Ejection and Disruption of Giant Planets," The Astrophysical Journal, 732, 74.

 

       The discovery of Jupiter-mass planets in close orbits about their parent stars has challenged models of planet formation. Recent observations have shown that a number of these planets have highly inclined, sometimes retrograde orbits about their parent stars, prompting much speculation as to their origin. It is known that migration alone cannot account for the observed population of these misaligned hot Jupiters, which suggests that dynamical processes after the gas disk dissipates play a substantial role in yielding the observed inclination and eccentricity distributions. One particularly promising candidate is planet-planet scattering, which is not very well understood in the nonlinear regime of tides. Through three-dimensional hydrodynamical simulations of multi-orbit encounters, we show that planets that are scattered into an orbit about their parent stars with closest approach distance being less than approximately three times the tidal radius are either destroyed or completely ejected from the system. We find that as few as 9 and as many as 12 of the currently known hot Jupiters have a maximum initial apastron for scattering that lies well within the ice line, implying that these planets must have migrated either before or after the scattering event that brought them to their current positions. If stellar tides are unimportant (Q * >~ 107), disk migration is required to explain the existence of the hot Jupiters present in these systems. Additionally, we find that the disruption and/or ejection of Jupiter-mass planets deposits a Sun's worth of angular momentum onto the host star. For systems in which planet-planet scattering is common, we predict that planetary hosts have up to a 35% chance of possessing an obliquity relative to the invariable plane of greater than 90°.

 

 

 

Hadjidemetriou, J.D., Voyatzis, G., 2011, "The 1/1 resonance in extrasolar systems," Celestial Mechanics and Dynamical Astronomy, 19.

 

       We present families of symmetric and asymmetric periodic orbits at the 1/1 resonance, for a planetary system consisting of a star and two small bodies, in comparison to the star, moving in the same plane under their mutual gravitational attraction. The stable 1/1 resonant periodic orbits belong to a family which has a planetary branch, with the two planets moving in nearly Keplerian orbits with non zero eccentricities and a satellite branch, where the gravitational interaction between the two planets dominates the attraction from the star and the two planets form a close binary which revolves around the star. The stability regions around periodic orbits along the family are studied. Next, we study the dynamical evolution in time of a planetary system with two planets which is initially trapped in a stable 1/1 resonant periodic motion, when a drag force is included in the system. We prove that if we start with a 1/1 resonant planetary system with large eccentricities, the system migrates, due to the drag force, along the family of periodic orbits and is finally trapped in a satellite orbit. This, in principle, provides a mechanism for the generation of a satellite system: we start with a planetary system and the final stage is a system where the two small bodies form a close binary whose center of mass revolves around the star.

 

 

Harbison, R.A., Thomas, P.C., Nicholson, P.C., 2011, "Rotational modeling of Hyperion," Celestial Mechanics and Dynamical Astronomy, 110, 1-16.

 

       Saturn's moon, Hyperion, is subject to strongly-varying solid body torques from its primary and lacks a stable spin state resonant with its orbital frequency. In fact, its rotation is chaotic, with a Lyapunov timescale on the order of 100 days. In 2005, Cassini made three close passes of Hyperion at intervals of 40 and 67 days, when the moon was imaged extensively and the spin state could be measured. Curiously, the spin axis was observed at the same location within the body, within errors, during all three fly-bys.~ 30° from the long axis of the moon and rotating between 4.2 and 4.5 times faster than the synchronous rate. Our dynamical modeling predicts that the rotation axis should be precessing within the body, with a period of ~ 16 days. If the spin axis retains its orientation during all three fly-bys, then this puts a strong constraint on the in-body precessional period, and thus the moments of inertia. However, the location of the principal axes in our model are derived from the shape model of Hyperion, assuming a uniform composition. This may not be a valid assumption, as Hyperion has significant void space, as shown by its density of 544± 50 kg m -3 (Thomas et al. in Nature 448:50). This paper will examine both a rotation model with principal axes fixed by the shape model, and one with offsets from the shape model. We favor the latter interpretation, which produces a best-fit with principal axes offset of ~ 30° from the shape model, placing the A axis at the spin axis in 2005, but returns a lower reduced  χ 2 than the best-fit fixed-axes model.

 

 

 

Hoyer, S., Rojo, P., Ló-Morales, M., Dí, R.F., Chambers, J., Minniti, D., 2011, "Five New Transit Epochs of the Exoplanet OGLE-TR-111b," The Astrophysical Journal, 733, 53.

 

       We report five new transit epochs of the extrasolar planet OGLE-TR-111b, observed in the v-HIGH and Bessell I bands with the FORS1 and FORS2 at the ESO Very Large Telescope between 2008 April and May. The new transits have been combined with all previously published transit data for this planet to provide a new transit timing variations (TTVs) analysis of its orbit. We find no TTVs with amplitudes larger than 1.5 minutes over a four-year observation time baseline, in agreement with the recent result by Adams et al. Dynamical simulations fully exclude the presence of additional planets in the system with masses greater than 1.3, 0.4, and 0.5 M ⊕ at the 3:2, 1:2, and 2:1 resonances, respectively. We also place an upper limit of about 30 M ⊕ on the mass of potential second planets in the region between the 3:2 and 1:2 mean-motion resonances.

 

 

Iorio, L., 2011, "On the anomalous secular increase of the eccentricity of the orbit of the Moon," Monthly Notices of the Royal Astronomical Society, 706.

 

       A recent analysis of a Lunar Laser Ranging (LLR) data record spanning 38.7 yr revealed an anomalous increase of the eccentricity e of the lunar orbit amounting to de/dtmeas = (9 +/- 3) 10-12 yr-1. The present-day models of the dissipative phenomena occurring in the interiors of both the Earth and the Moon are not able to explain it. In this paper, we examine several dynamical effects, not modelled in the data analysis, in the framework of long-range modified models of gravity and of the standard Newtonian/Einsteinian paradigm. It turns out that none of them can accommodate ?. Many of them do not even induce long-term changes in e; other models do, instead, yield such an effect, but the resulting magnitudes are in disagreement with ?. In particular, the general relativistic gravitomagnetic acceleration of the Moon due to the Earth's angular momentum has the right order of magnitude, but the resulting Lense-Thirring secular effect for the eccentricity vanishes. A potentially viable Newtonian candidate would be a trans-Plutonian massive object (Planet X/Nemesis/Tyche) since it, actually, would affect e with a non-vanishing long-term variation. On the other hand, the values for the physical and orbital parameters of such a hypothetical body required to obtain at least the right order of magnitude for ? are completely unrealistic: suffices it to say that an Earth-sized planet would be at 30 au, while a jovian mass would be at 200 au. Thus, the issue of finding a satisfactorily explanation for the anomalous behaviour of the Moon's eccentricity remains open.

 

 

Johansen, A., Klahr, H., Henning, T., 2011, "High-resolution simulations of planetesimal formation in turbulent protoplanetary discs," Astronomy and Astrophysics, 529, 62.

 

       We present high-resolution computer simulations of dust dynamics and planetesimal formation in turbulence generated by the magnetorotational instability. We show that the turbulent viscosity associated with magnetorotational turbulence in a non-stratified shearing box increases when going from 2563 to 5123 grid points in the presence of a weak imposed magnetic field, yielding a turbulent viscosity of α ≈ 0.003 at high resolution. Particles representing approximately meter-sized boulders concentrate in large-scale high-pressure regions in the simulation box. The appearance of zonal flows and particle concentration in pressure bumps is relatively similar at moderate (2563) and high (5123) resolution. In the moderate-resolution simulation we activate particle self-gravity at a time when there is little particle concentration, in contrast with previous simulations where particle self-gravity was activated during a concentration event. We observe that bound clumps form over the next ten orbits, with initial birth masses of a few times the dwarf planet Ceres. At high resolution we activate self-gravity during a particle concentration event, leading to a burst of planetesimal formation, with clump masses ranging from a significant fraction of to several times the mass of Ceres. We present a new domain decomposition algorithm for particle-mesh schemes. Particles are spread evenly among the processors and the local gas velocity field and assigned drag forces are exchanged between a domain-decomposed mesh and discrete blocks of particles. We obtain good load balancing on up to 4096 cores even in simulations where particles sediment to the mid-plane and concentrate in pressure bumps.

 

 

Jura, M., 2011, "An Upper Bound to the Space Density of Interstellar Comets," The Astronomical Journal, 141, 155.

 

       Two well-studied white dwarfs with helium-dominated atmospheres (DBs) each possess less hydrogen than carried by a single average-mass comet. Plausibly, the wind rates from these stars are low enough that most accreted hydrogen remains with the star. If so, and presuming their nominal effective temperatures, then these DBs have faced minimal impact by interstellar comets during their 50 Myr cooling age; interstellar iceballs with radii between 10 m and 2 km contain less than 1% of all interstellar oxygen. This analysis suggests that most stars do not produce comets at the rate predicted by "optimistic" scenarios for the formation of the Oort Cloud.

 

 

 

Kazeminejad, B., Atkinson, D.H., Lebreton, J.-P., 2011, "Titan.s new pole: Implications for the Huygens entry and descent trajectory and landing coordinates," Advances in Space Research, 47, 1622-1632.

 

       The European Space Agency.s Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC). It performed a successful entry and descent sequence and softly landed on Titan.s surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. Since the publication of the official project entry and descent trajectory reconstruction effort by the Descent Trajectory Working Group in 2007 (referred to as DTWG#4) various other efforts have been performed and published. This paper presents an overview of the most relevant reconstructions and compares their methodologies and results. Furthermore, the results of a new reconstruction effort (DTWG#5) are presented, which is based on the same methodology as DTWG#4 but takes into account new estimates of Titan.s pole coordinates which were derived from radar images of different Cassini Titan flybys. It can be shown that the primary effect can be observed in the meridional direction which is represented by a stark southward shift of the trajectory by about 0.3 deg. A much smaller effect is seen in the zonal direction (i.e., less than 0.01 deg in the west to east direction). The revised probe landing coordinates are 192.335 deg W and 10.573 deg S. A comparison of these coordinates with results of recent landing site investigations using visual and radar images of the Cassini VIMS instrument shows excellent agreement of the two independently derived landing coordinates, i.e., longitude and latitude residuals of respectively 0.035 deg and 0.007 deg.

 

 

Kör, R., 2011, "The orbit of GG Tauri A," Astronomy and Astrophysics, 530, 126.

 

Aims: We present a study of the orbit of the pre-main-sequence binary system GG Tau A and its relation to its circumbinary disk, in order to find an explanation for the sharp inner edge of the disk.

 

Methods: Three new relative astrometric positions of the binary were obtained with NACO at the VLT. We combine them with data from the literature and fit orbit models to the dataset.

 

Results: We find that an orbit coplanar with the disk and compatible with the astrometric data is too small to explain the inner gap of the disk. On the other hand, orbits large enough to cause the gap are tilted with respect to the disk. If the disk gap is indeed caused by the stellar companion, then the most likely explanation is a combination of underestimated astrometric errors and a misalignment between the planes of the disk and the orbit.

 

 

Koot, L., de Viron, O., 2011, "Atmospheric contributions to nutations and implications for the estimation of deep Earth's properties from nutation observations," Geophysical Journal International, 185, 1255-1265.

 

       We propose a new estimation of the atmospheric contributions to Earth's nutations based on three reanalyses of atmospheric global circulation models (GCM), namely the two reanalyses of the National Center for Environmental Prediction (NCEP) and the ERA-40 reanalysis of the European Center for Medium-Range Weather Forecasts (ECMWF). We estimate the complex amplitudes of the periodic terms in the atmospheric forcing and convolve them with a transfer function for a three-layers Earth with an anelastic mantle and dissipative couplings at the fluid core boundaries. Unlike previous estimations based on operational GCMs, the results we obtain here from the three reanalysis GCMs are in good agreement, which makes them more reliable. From a joint inversion of the three atmospheric models on their common time span (from 1979 to 2002.3), we estimate the atmospheric contributions to nutations to be -38.2 ± 0.4 μas in-phase (ip) and 65.1 ± 0.4 μas out-of-phase (op) on the prograde annual term (S1), -64 ± 5 μas ip and 29 ± 5 μas op on the retrograde annual term (ψ1), and -11.3 ± 0.3 μas ip and 41.5 ± 0.3 μas op on the prograde semi-annual term (P1). As the atmospheric contributions to nutation vary in time, we also compute their time-variability on the time span from 1979 to 2010. In particular, we show that the contribution to ψ1has a very large time variability but that these variations are well determined by the atmospheric models that we use. Finally, we explore the implications of the atmospheric contribution to ψ1 on the estimation of Earth's deep interior properties from nutation observations. We show that this contribution is too small to affect significantly the estimation of these properties.

 

 

Kubo, Y., 2011, "Kinematical modeling of the Earth rotation, focusing on the Oppolzer terms in a rigid Earth and the Oppolzer-like terms in an elastic Earth," Celestial Mechanics and Dynamical Astronomy, 110, 143-168.

 

       Under perturbations from outer bodies, the Earth experiences changes of its angular momentum axis, figure axis and rotational axis. In the theory of the rigid Earth, in addition to the precession and nutation of the angular momentum axis given by the Poisson terms, both the figure axis and the rotational axis suffer forced deviation from the angular momentum axis. This deviation is expressed by the so-called Oppolzer terms describing separation of the averaged figure axis, called CIP (Celestial Intermediate Pole) or CEP (Celestial Ephemeris Pole), and the mathematically defined rotational axis, from the angular momentum axis. The CIP is the rotational axis in a frame subject to both precession and nutation, while the mathematical rotational axis is that in the inertial (non-rotating) frame. We investigate, kinematically, the origin of the separation between these two axes - both for the rigid Earth and an elastic Earth. In the case of an elastic Earth perturbed by the same outer bodies, there appear further deviations of the figure and rotational axes from the angular momentum axis. These deviations, though similar to the Oppolzer terms in the rigid Earth, are produced by quite a different physical mechanism. Analysing this mechanism, we derive an expression for the Oppolzer-like terms in an elastic Earth. From this expression we demonstrate that, under a certain approximation (in neglect of the motion of the perturbing outer bodies), the sum of the direct and convective perturbations of the spin axis coincides with the direct perturbation of the figure axis. This equality, which is approximate, gets violated when the motion of the outer bodies is taken into account.

 

 

 

Lambert, S.B., Le Poncin-Lafitte, C., 2011, "Improved determination of γ by VLBI," Astronomy and Astrophysics, 529, 70.

 

       Aims: This study revisits the estimate of the post-Newtonian relativistic parameter γ reported previously. We use (i) improved geophysical and astronomical modeling in the analysis software package, and (ii) a higher number of observations, a large part of which come from a relatively small number of VLBA experiments at 8 GHz. 

Methods: We analyzed more than seven million group delays measured by very long baseline interferometry between August 1979 and August 2010. The parameter γ was least squares fitted to delays as a global parameter over the entire observational time period. 

Results: The most complete solution of this study yielded γ = 0.99992 ± 0.00012, whereas it was 0.99984 ± 0.00015 in our 2009 paper. The item (i), which is recognized as important for geodesy and reference frame realization, provides estimates of |γ - 1| that are smaller than 10-4. As expected, the formal error in γ decreases when additional sessions are processed. In particular, we demonstrate that the inclusion of more than 1.7 million observations from the VLBA (mainly from the RDV and VLBA calibrator survey experiments) in the analysis decreases the formal error in the estimate of γ by about 15% with respect to our previous determination.

 

 

Lanza, A.F., Damiani, C., Gandolfi, D., 2011, "Constraining tidal dissipation in F-type main-sequence stars: the case of CoRoT-11," Astronomy and Astrophysics, 529, 50.

 

       Context. Tidal dissipation in late-type stars is presently poorly understood and the study of planetary systems hosting hot Jupiters can provide new observational constraints to test proposed theories. 
Aims: We focus on systems with F-type main-sequence stars and find that the recently discovered system CoRoT-11 is presently the best suited for this kind of investigation. 

Methods: A classic constant tidal lag model is applied to reproduce the evolution of the system from a plausible nearly synchronous state on the zero-age main sequence (ZAMS) to the present state, thus putting constraints on the average modified tidal quality factor < Q_s' > of its F6V star.Initial conditions with the stellar rotation period longer than the orbital period of the planet can be excluded on the basis of the presently observed state in which the star spins faster than the planet orbit. 

Results: It is found that 4 ×106 ≲ < Q_s' > ≲ 2 ×107, if the system started its evolution on the ZAMS close to synchronization, with an uncertainty related to the constant tidal lag hypothesis and the estimated stellar magnetic braking within a factor of ≈5-6.For a non-synchronous initial state of the system, < Qs' > ≲ 4 ×106 implies an age younger than ~1 Gyr, while < Q_s' > ≳ 2 ×107 may be tested by comparing the theoretically derived initial orbital and stellar rotation periods with those of a sample of observed systems. Moreover, we discuss how the present value of Qs' can be measured by a timing of the mid-epoch and duration of the transits as well as of the planetary eclipses to be observed in the infrared with an accuracy of ~0.5-1 s over a time baseline of ~25 yr. 

Conclusions: CoRoT-11 is a highly interesting system that potentially allows us a direct measure of the tidal dissipation in an F-type star as well as the detection of the precession of the orbital plane of the planet that provides us with an accurate upper limit for the obliquity of the stellar equator. If the planetary orbit has a significant eccentricity (e ≳ 0.05), it will be possible to also detect the precession of the line of the apsides and derive information on the Love number of the planet and its tidal quality factor.

 

Lara, M., Fukushima, T., Ferrer, S., 2011, "Ceres' rotation solution under the gravitational torque of the Sun," Monthly Notices of the Royal Astronomical Society, 712.

 

       Available observations of the shape of Ceres show it as a rotationally symmetric oblate spheroid. However, deviations from axisymmetry even at the level of observational accuracy may show significant effects on its rotational dynamics. These presumed deviations can be accounted for in a purely analytical way by means of perturbation theory. In our approach, the spherical rotor is taken as the unperturbed part of the motion instead of the more common torque-free motion or uniaxial body approaches. This alternative allows us to compute an analytical solution for the rotation of Ceres under the gravitational pull of the Sun by proceeding with a successive elimination of the different angles, which only involves quadratures of straightforward computation.

 

 

Lee, K.J., Wex, N., Kramer, M., Stappers, B.W., Bassa, C.G., Janssen, G.H., Karuppusamy, R., Smits, R., 2011, "Gravitational wave astronomy of single sources with a pulsar timing array," Monthly Notices of the Royal Astronomical Society, 628.

 

The stability of radio millisecond pulsars as celestial clocks allows for the possibility to detect and study the properties of gravitational waves (GWs) when the received pulses are timed jointly in a 'Pulsar Timing Array' (PTA) experiment. Here, we investigate the potential of detecting the GW from individual binary black hole systems using PTAs and calculate the accuracy for determining the GW properties. This is done in a consistent analysis, which at the same time accounts for the measurement of the pulsar distances via the timing parallax.

 

We find that, at low redshift, a PTA is able to detect the nano-hertz GW from super-massive black hole binary systems with masses of .108-1010 Mȯ less than .105 yrs before the final merger. Binaries with more than .103-104 yr before merger are effectively monochromatic GW, and those with less than .103-104 yr before merger may allow us to detect the evolution of binaries.

 

For our findings, we derive an analytical expression to describe the accuracy of a pulsar distance measurement via timing parallax. We consider 5 yr of bi-weekly observations at a precision of 15 ns for close-by (.0.5-1 kpc) pulsars. Timing 20 pulsars would allow us to detect a GW source with an amplitude larger than 5 ×10-17. We calculate the corresponding GW and binary orbital parameters and their measurement precision. The accuracy of measuring the binary orbital inclination angle, the sky position and the GW frequency is calculated as functions of the GW amplitude. We note that the 'pulsar term', which is commonly regarded as noise, is essential for obtaining an accurate measurement for the GW source location.

 

We also show that utilizing the information encoded in the GW signal passing the Earth also increases the accuracy of pulsar distance measurements. If the GW is strong enough, one can achieve sub-parsec distance measurements for nearby pulsars with distance less than .0.5-1 kpc.

 

 

Libert, A.-S., Hubaux, C., Carletti, T., 2011, "The Global Symplectic Integrator: an efficient tool for stability studies of dynamical systems. Application to the Kozai resonance in the restricted three-body problem," Monthly Notices of the Royal Astronomical Society, 414, 659-667.

 

       Following the discovery of extrasolar systems, the study of long-term evolution and stability of planetary systems is enjoying a renewed interest. While non-symplectic integrators are very time-consuming because of the very long time-scales and the small integration steps required to have a good energy preservation, symplectic integrators are well suited for the study of such orbits on long time-spans. However, stability studies of dynamical systems generally rely on non-symplectic integrations of deviation vectors. In this work we propose a numerical approach to distinguish between regular and chaotic orbits in Hamiltonian systems, hereby called Global Symplectic Integrator. It consists of the simultaneous integration of the orbit and the deviation vectors using a symplectic scheme of any order. In particular, due to its symplectic properties, the proposed method allows us to recover the correct orbit characteristics using very large integration time-steps, fluctuations of energy around a constant value and short CPU times. It proves to be more efficient than non-symplectic schemes to correctly identify the behaviour of a given orbit, especially on dynamics acting on long time-scales. To illustrate the numerical performances of the global symplectic integrator, we will apply it to the well-known toy problem of Hén-Heiles and the challenging problem of the Kozai resonance in the restricted three-body problem, whose secular effects have periods of the order of 104-105 yr.

 

 

Lin, M.-K., Papaloizou, J.C.B., 2011, "Edge modes in self-gravitating disc-planet interactions," Monthly Notices of the Royal Astronomical Society, 876.

 

       We study the stability of gaps opened by a giant planet in a self-gravitating protoplanetary disc. We find a linear instability associated with both the self-gravity of the disc and local vortensity maxima which coincide with gap edges. For our models, these edge modes develop and extend to twice the orbital radius of a Saturn mass planet in discs with total masses Md≳ 0.06M*, where M* is the central stellar mass, corresponding to a Toomre Q≲ 1.5 at twice the planet's orbital radius. The disc models, although massive, are such that they are stable in the absence of the planet. Unlike the previously studied local vortex forming instabilities associated with gap edges in weakly or non-self-gravitating discs with low viscosity, the edge modes we consider are global and exist only in sufficiently massive discs, but for the typical viscosity values adopted for protoplanetary discs. It is shown through analytic modelling and linear calculations that edge modes may be interpreted as a localized disturbance associated with a gap edge inducing activity in the extended disc, through the launching of density waves excited through gravitational potential perturbation at Lindblad resonances. We also perform hydrodynamic simulations in order to investigate the evolution of edge modes in the linear and non-linear regimes in disc-planet systems. The form and growth rates of developing unstable modes are found to be consistent with linear theory. Their dependence on viscosity and gravitational softening is also explored. We also performed a first study of the effect of edge modes on disc-planet torques and the orbital migration of the planet. We found that if edge modes develop, then the average torque on the planet becomes more positive with increasing disc mass. In simulations where the planet was allowed to migrate, although a fast type III migration could be seen that was similar to that seen in non-self-gravitating discs, we found that it was possible for the planet to interact gravitationally with the spiral arms associated with an edge mode and that this could result in the planet being scattered outwards. Thus orbital migration is likely to be complex and non-monotonic in massive discs of the type we consider.

 

 

Liu, H., Zhou, J.-L., Wang, S., 2011, "Modeling Planetary System Formation with N-body Simulations: Role of Gas Disk and Statistics Compared to Observations," The Astrophysical Journal, 732, 66.

 

       During the late stage of planet formation, when Mars-sized cores appear, interactions among planetary cores can excite their orbital eccentricities, accelerate their merging, and thus sculpt their final orbital architecture. This study contributes to the final assembling of planetary systems with N-body simulations, including the type I or II migration of planets and gas accretion of massive cores in a viscous disk. Statistics on the final distributions of planetary masses, semimajor axes, and eccentricities are derived and are comparable to those of the observed systems. Our simulations predict some new orbital signatures of planetary systems around solar mass stars: 36% of the surviving planets are giant planets (>10 M ⊕). Most of the massive giant planets (>30 M ⊕) are located at 1-10 AU. Terrestrial planets are distributed more or less evenly at <1-2 AU. Planets in inner orbits may accumulate at the inner edges of either the protostellar disk (3-5 days) or its magnetorotational instability dead zone (30-50 days). There is a planet desert in the mass-eccentricity diagram, i.e., a lack of planets with masses 0.005-0.08MJ in highly eccentric orbits (e > 0.3-0.4). The average eccentricity (~0.15) of the giant planets (>10 M⊕) is greater than that (~0.05) of the terrestrial planets (<10 M ⊕). A planetary system with more planets tends to have smaller planet masses and orbital eccentricities on average.

 

 

Liu, X., Baoyin, H., Ma, X., 2011, "Equilibria, periodic orbits around equilibria, and heteroclinic connections in the gravity field of a rotating homogeneous cube," Astrophysics and Space Science, 333, 409-418.

 

       This paper investigates the dynamics of a particle orbiting around a rotating homogeneous cube, and shows fruitful results that have implications for examining the dynamics of orbits around non-spherical celestial bodies. This study can be considered as an extension of previous research work on the dynamics of orbits around simple shaped bodies, including a straight segment, a circular ring, an annulus disk, and simple planar plates with backgrounds in celestial mechanics. In the synodic reference frame, the model of a rotating cube is established, the equilibria are calculated, and their linear stabilities are determined. Periodic orbits around the equilibria are computed using the traditional differential correction method, and their stabilities are determined by the eigenvalues of the monodromy matrix. The existence of homoclinic and heteroclinic orbits connecting periodic orbits around the equilibria is examined and proved numerically in order to understand the global orbit structure of the system. This study contributes to the investigation of irregular shaped celestial bodies that can be divided into a set of cubes.

 

 

Martin, R.G., Lubow, S.H., 2011, "Tidal truncation of circumplanetary discs," Monthly Notices of the Royal Astronomical Society, 413, 1447-1461.

 

       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.

 

 

 

Minton, D.A., Malhotra, R., 2011, "Secular Resonance Sweeping of the Main Asteroid Belt During Planet Migration," The Astrophysical Journal, 732, 53.

 

       We calculate the eccentricity excitation of asteroids produced by the sweeping ν6 secular resonance during the epoch of planetesimal-driven giant planet migration in the early history of the solar system. We derive analytical expressions for the magnitude of the eccentricity change and its dependence on the sweep rate and on planetary parameters; the ν6 sweeping leads to either an increase or a decrease of eccentricity depending on an asteroid's initial orbit. Based on the slowest rate of ν6 sweeping that allows a remnant asteroid belt to survive, we derive a lower limit on Saturn's migration speed of ~0.15 AU Myr-1 during the era that the ν6 resonance swept through the inner asteroid belt (semimajor axis range 2.1-2.8 AU). This rate limit is for Saturn's current eccentricity and scales with the square of its eccentricity; the limit on Saturn's migration rate could be lower if its eccentricity were lower during its migration. Applied to an ensemble of fictitious asteroids, our calculations show that a prior single-peaked distribution of asteroid eccentricities would be transformed into a double-peaked distribution due to the sweeping of the ν6 resonance. Examination of the orbital data of main belt asteroids reveals that the proper eccentricities of the known bright (H <= 10.8) asteroids may be consistent with a double-peaked distribution. If so, our theoretical analysis then yields two possible solutions for the migration rate of Saturn and for the dynamical states of the pre-migration asteroid belt: a dynamically cold state (single-peaked eccentricity distribution with mean of ~0.05) linked with Saturn's migration speed ~4 AU Myr-1 or a dynamically hot state (single-peaked eccentricity distribution with mean of ~0.3) linked with Saturn's migration speed ~0.8 AU Myr-1.

 

 

Mitrovica, J.X., Wahr, J., 2011, "Ice Age Earth Rotation *," Annual Review of Earth and Planetary Sciences, 39, 577-616.

 

       Modern predictions of the rotational stability of an ice age Earth reflect a convergence of two classic problems in geophysical analysis -- the modeling of the glacial isostatic adjustment (GIA) process and the rotational stability of terrestrial planets. Recent theoretical advances in this area have been motivated not by conventional applications, such as the inference of Earth's deep-mantle viscosity, but rather by efforts to address vexing problems in global climate change research. These advances have demonstrated that traditional calculations of the ongoing motion of the rotation pole relative to the surface geography, or true polar wander (TPW), driven by ice age loading have systematically overestimated this motion by up to a factor of 4 by underestimating by .1% the background flattening of Earth's oblate form. The physics of this sensitivity is related to concepts that appear in canonical, mid-twentieth century discussions of Earth rotation, and avoiding the associated inaccuracy resolves numerous perplexing sensitivities evident in previous predictions of ice age TPW. Moreover, these updated predictions provide both an important step in reconciling a recently defined enigma of modern global sea-level rise and a robust framework for analyzing a suite of space-geodetic constraints on Earth's climate system.

 

 

MoóA., Frey, S., Lambert, S.B., Titov, O.A., Bakos, J., 2011, "On the Connection of the Apparent Proper Motion and the VLBI Structure of Compact Radio Sources," The Astronomical Journal, 141, 178.

 

       Many of the compact extragalactic radio sources that are used as fiducial points to define the celestial reference frame are known to have proper motions detectable with long-term geodetic/astrometric very long baseline interferometry (VLBI) measurements. These changes can be as high as several hundred microarcseconds per year for certain objects. When imaged with VLBI at milliarcsecond (mas) angular resolution, these sources (radio-loud active galactic nuclei) typically show structures dominated by a compact, often unresolved "core" and a one-sided "jet." The positional instability of compact radio sources is believed to be connected with changes in their brightness distribution structure. For the first time, we test this assumption in a statistical sense on a large sample rather than on only individual objects. We investigate a sample of 62 radio sources for which reliable long-term time series of astrometric positions as well as detailed 8 GHz VLBI brightness distribution models are available. We compare the characteristic direction of their extended jet structure and the direction of their apparent proper motion. We present our data and analysis method, and conclude that there is indeed a correlation between the two characteristic directions. However, there are cases where the ~1-10 mas scale VLBI jet directions are significantly misaligned with respect to the apparent proper motion direction.

 

 

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, 413, 554-572.

 

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.

 

 

Oberti, P., Pocart, B., 2011, "Intermediary orbits for oscillating motions," Astrophysics and Space Science, 333, 71-78.

 

       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.

 

 

Papaloizou, J.C.B., 2011, "Tidal interactions in multi-planet systems," Celestial Mechanics and Dynamical Astronomy, 23.

 

       We study systems of close orbiting planets evolving under the influence of tidal circularization. It is supposed that a commensurability forms through the action of disk induced migration and orbital circularization. After the system enters an inner cavity or the disk disperses the evolution continues under the influence of tides due to the central star which induce orbital circularization. We derive approximate analytic models that describe the evolution away from a general first order resonance that results from tidal circularization in a two planet system and which can be shown to be a direct consequence of the conservation of energy and angular momentum. We consider the situation when the system is initially very close to resonance and also when the system is between resonances. We also perform numerical simulations which confirm these models and then apply them to two and four planet systems chosen to have parameters related to the GJ 581 and

 

 

 

Pollney, D., Reisswig, C., 2011, "Gravitational Memory in Binary Black Hole Mergers," The Astrophysical Journal, 732, L13.

 

       In addition to the dominant oscillatory gravitational wave signals produced during binary inspirals, a non-oscillatory component arises from the nonlinear "memory" effect, sourced by the emitted gravitational radiation. The memory grows significantly during the late-inspiral and merger, modifying the signal by an almost step-function profile, and making it difficult to model by approximate methods. We use numerical evolutions of binary black holes (BHs) to evaluate the nonlinear memory during late-inspiral, merger, and ringdown. We identify two main components of the signal: the monotonically growing portion corresponding to the memory, and an oscillatory part which sets in roughly at the time of merger and is due to the BH ringdown. Counterintuitively, the ringdown is most prominent for models with the lowest total spin. Thus, the case of maximally spinning BHs anti-aligned to the orbital angular momentum exhibits the highest signal-to-noise ratio (S/N) for interferometric detectors. The largest memory offset, however, occurs for highly spinning BHs, with an estimated value of htot 20 ~= 0.24 in the maximally spinning case. These results are central to determining the detectability of nonlinear memory through pulsar timing array measurements.

 

 

Pont, F., Husnoo, N., Mazeh, T., Fabrycky, D., 2011, "Determining eccentricities of transiting planets: a divide in the mass-period plane," Monthly Notices of the Royal Astronomical Society, 414, 1278-1284.

 

       The two dominant features in the distribution of orbital parameters for close-in exoplanets are the prevalence of circular orbits for very short periods, and the observation that planets on closer orbits tend to be heavier. The first feature is interpreted as a signature of tidal evolution, while the origin of the second, a 'mass-period relation' for hot Jupiters, is not understood. In this paper we reconsider the ensemble properties of transiting exoplanets with well-measured parameters, focusing on orbital eccentricity and the mass-period relation. We recalculate the constraints on eccentricity in a homogeneous way, using new radial velocity data, with particular attention to statistical biases. We find that planets on circular orbits gather in a well-defined region of the mass-period plane, close to the minimum period for any given mass. Exceptions to this pattern reported in the literature can be attributed to statistical biases. The ensemble data is compatible with classical tide theory with orbital circularization caused by tides raised on the planet, and suggest that tidal circularization and the stopping mechanisms for close-in planets are closely related to each other. The position mass-period relation is compatible with a relation between a planet's Hill radius and its present orbit.

 

 

Qian, S.-B., Liu, L., Liao, W.-P., Li, L.-J., Zhu, L.-Y., Dai, Z.-B., He, J.-J., Zhao, E.-G., Zhang, J., Li, K., 2011, "Detection of a planetary system orbiting the eclipsing polar HU Aqr," Monthly Notices of the Royal Astronomical Society, 414, L16-L20.

 

       Using the precise times of mid-egress of the eclipsing polar HU Aqr, we discovered that this polar is orbited by two or more giant planets. The two planets detected so far have masses of at least 5.9 and 4.5MJup. Their respective distances from the polar are 3.6 and 5.4 au with periods of 6.54 and 11.96 yr, respectively. The observed rate of decrease of period derived from the downward parabolic change in the observed - calculated (O - C) curve is a factor of 15 larger than the value expected for gravitational radiation. This indicates that it may be only a part of a long-period cyclic variation, revealing the presence of one more planet. It is interesting to note that the two detected circumbinary planets follow the Titus-Bode law of solar planets with n= 5 and 6. We estimate that another 10 yr of observations will reveal the presence of the predicted third planet.

 

 

 

Rein, H., Tremaine, S., 2011, "Symplectic integrators in the shearing sheet," Monthly Notices of the Royal Astronomical Society, 845.

 

       The shearing sheet is a model dynamical system that is used to study the small-scale dynamics of astrophysical discs. Numerical simulations of particle trajectories in the shearing sheet usually employ the leapfrog integrator, but this integrator performs poorly because of velocity-dependent (Coriolis) forces. We describe two new integrators for this purpose; both are symplectic, time-reversible and second-order accurate, and can easily be generalized to higher orders. Moreover, both the integrators are exact when there are no small-scale forces such as mutual gravitational forces between disc particles. In numerical experiments these integrators have errors that are often several orders of magnitude smaller than competing methods. The first of our new integrators (.SEI.) is well suited for discs in which the typical interparticle separation is large compared to the particles. Hill radii (e.g., planetary rings), and the second one (.SEKI.) is designed for discs in which the particles are on bound orbits or the separation is smaller than the Hill radius (e.g. irregular satellites of the giant planets).

 

 

Rodríez, A., Ferraz-Mello, S., Michtchenko, T.A., BeaugéC., Miloni, O., 2011, "Tidal decay and orbital circularization in close-in two-planet systems," Monthly Notices of the Royal Astronomical Society, 800.

 

       The motion of two planets around a Sun-like star under the combined effects of mutual interaction and tidal dissipation is investigated. The secular behaviour of the system is analysed using two different approaches. First, we solve the exact equations of motion through the numerical simulation of the system evolution. In addition to the orbital decay and circularization, we show that the final configuration of the system is affected by the shrinking of the inner orbit. Our second approach consists of the analysis of the stationary solutions of mean equations of motion based on a Hamiltonian formalism. We consider the case of a hot super-Earth planet with a more massive outer companion. As a real example, the CoRoT-7 system is analysed, solving the exact and mean equations of motion. The star-planet tidal interaction produces orbital decay and circularization of the orbit of CoRoT-7b. In addition, the long-term tidal evolution is such that the eccentricity of CoRoT-7c is also circularized and a pair of final circular orbits is obtained. A curve in the space of eccentricities can be constructed through the computation of stationary solutions of mean equations including dissipation. The application to the CoRoT-7 system shows that the stationary curve agrees with the result of numerical simulations of exact equations. A similar investigation performed in a super-Earth-Jupiter two-planet system shows that the doubly circular state is accelerated when there is a significant orbital migration of the inner planet, in comparison with previous results where migration is neglected.

 

 

Roy, K., Peltier, W.R., 2011, "GRACE era secular trends in Earth rotation parameters: A global scale impact of the global warming process?," Geophysical Research Letters, 38, 10306.

 

       Recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail, namely those associated with the speed and direction of polar wander and with the non-tidal acceleration of the rate of axial rotation (via the measurement of the changing oblateness of the Earth's shape). It is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992. It is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets, and from the very large number of small ice-sheets and glaciers that are also being influenced by the global warming phenomenon. The modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the Gravity Recovery and Climate Experiment (GRACE). These changes in secular rates might greatly assist in understanding why the GRACE-inferred values of the time derivatives of the degree two and order one Stokes coefficients differ so significantly from those associated with Late Quaternary ice-age influence.

 

 

Schaeffer, N., Pais, M.A., 2011, "On symmetry and anisotropy of Earth-core flows," Geophysical Research Letters, 38, 10309.

 

       Quasi-geostrophic (QG) flows are a recently developed and very promising paradigm for modeling decadal secular variation (SV). Here we examine the effects of allowing anisotropy and departures of the flow from quasigeostrophy. We perform dedicated numerical experiments of the flow dynamics and magnetic induction inside the Earth's liquid core at time scales characteristic of secular variation of the geomagnetic field. Obtained results motivate new flow inversion regularization featuring an equatorially anti-symmetric component superimposed to quasi-geostrophic columns, and stronger latitudinal than longitudinal flow gradients. Applying these constraints allows to explain the observed SV for the whole period 1840.2010, and most significantly, provides a clearly improvement in prediction for decadal length-of-day variations for the period 1980.2000. Furthermore, the trace of the inner-core appears clearly without any assumption for the 1997.2010 period covered by satellite geomagnetic data. Our results support QG being the appropriate description of the force balance within the core on decadal time scales and large spatial scales.

 

 

 

 

Sharma, B.K., 2011, "The Architectural Design Rules of Solar Systems Based on the New Perspective," Earth Moon and Planets, 108, 15-37.

 

       In this paper I present a new perspective of the birth and evolution of Planetary Systems. This new perspective presents an all encompassing and self consistent Paradigm of the birth and evolution of the solar systems. In doing so it redefines astronomy and rewrites astronomical principles. Kepler and Newton defined a stable and non-evolving elliptical orbits. While this perspective defines a collapsing or expanding spiral orbit of planets except for Brown Dwarfs. Brown Dwarfs are significant fraction of the central star. Hence they rapidly evolve from non-Keplerian state to the end point which is a Keplerian state where it is in stable elliptical orbits. On the basis of the Lunar Laser Ranging Data released by NASA on the Silver Jubilee Celebration of Man's Landing on Moon on 21st July 1969-1994, theoretical formulation of Earth-Moon tidal interaction was carried out and Planetary Satellite Dynamics was established. It was found that this mathematical analysis could as well be applied to Star and Planets system and since every star could potentially contain an extra-solar system, hence we have a large ensemble of exo-planets to test our new perspective on the birth and evolution of solar systems. Till date 403 exo-planets have been discovered in 390 extra-solar systems by radial velocity method, by transiting planet method, by gravitational lensing method, by direct imaging method and by timing method. I have taken 12 single planet systems, four Brown Dwarf - Star systems and two Brown Dwarf pairs. Following architectural design rules are corroborated through this study of exo-planets. All planets are born at inner Clarke's Orbit what we refer to as inner geo-synchronous orbit in case of Earth-Moon System. The inner Clarke's Orbit is an orbit of unstable equilibrium. By any perturbative force such as cosmic particles or radiation pressure, the planet gets tipped long of aG1 or short of aG1. Here aG1is inner Clarke's Orbit. If planet is long of aG1 then it is said to be in extra-synchronous orbit. Here Gravitational Sling Shot effect is in play. In gravity assist planet fly-by maneuver in space flights, gravitational sling shot is routinely used to boost the space craft to its destination. The exo-planet can either be launched on death spiral as CLOSE HOT JUPITERS or can be launched on an expanding spiral path as the planets in our Solar System are. In death spiral, exo-planet less than 5 mJ will get pulverized and vaporized in close proximity to the host star. If the mass is between 5 and 7.5 mJ then it will be partially vaporized and partially engulfed by the host star and if it is greater than 7.5 mJ, then it will be completely ingested by the host star. In the process the planet will deposit all its material and angular momentum in the Host Star. This will leave tell-tale imprints of ingestion: in such cases host Star will have higher 7Li, host star will become a rapidly rotating progenitor and the host star will have excess IR. All these have been confirmed by observations of Transiting Planets. It was also found that if the exo-planet are significant fraction of the host star then those exo-planets rapidly migrate from aG1 to aG2 and have very short Time Constant of Evolution as Brown Dwarfs have. But if exo-planets are insignificant fraction of the host star as our terrestrial planets are then they are stay put in their original orbit of birth. By corollary this implies that Giant exo-planets reach nearly Unity Evolution Factor in a fraction of the life span of a solar system. This is particularly true for brown dwarfs orbiting main sequence stars. In this study four star systems hosting Brown Dwarfs, two Brown Dwarf pairs and 12 extrasolar systems hosting Jupiter sized planets are selected. In Brown Dwarfs evolution factor is invariably UNITY or near UNITY irrespective of their respective age and Time Constant of Evolution is very short of the order of year or tens of years. In case of 12 exo-planets system with increasing mass ratio evolution factor increases and time constant of evolution shortens from Gy to My though there are two exceptions. TW Hydrae is a special case. This Solar System is newly born system which is only 9 million years old. Hence its exo-planet has just been born and it is very near its birth place just as predicted by my hypothesis. In fact it is only slightly greater than aG1. This vindicates our basic premise that planets are always born at inner Clarke's Orbit. This study vindicates the design rules which had been postulated at 35th COSPAR Scientific Assembly in 2004 at Paris, France, under the title "New Perspective on the Birth & Evolution of Solar Systems".

 

 

Singh, J., 2011, "Nonlinear stability in the restricted three-body problem with oblate and variable mass," Astrophysics and Space Science, 333, 61-69.

 

       This study investigates the nonlinear stability of the triangular equilibrium points when the bigger primary is an oblate spheroid and the infinitesimal body varies (decreases) it's mass in accordance with Jeans' law. It is found that these points are stable for all mass ratios in the range of linear stability except for three mass ratios depending upon oblateness coefficient A and b a constant due to the variation in mass governed by Jeans' law.

 

 

Tereno, I., Semboloni, E., Schrabback, T., 2011, "COSMOS weak-lensing constraints on modified gravity," Astronomy and Astrophysics, 530, 68.

 

       The observed acceleration of the universe, explained through dark energy, could alternatively be explained through a modification of gravity that would also induce modifications in the evolution of cosmological perturbations. We use new weak lensing data from the COSMOS survey to test for deviations from general relativity (GR). The departure from GR is parametrized in a model-independent way that consistently parametrizes the two-point cosmic shear amplitude and growth. Using CMB priors, we perform a likelihood analysis. We find constraints on the amplitude of the signal that do not indicate a deviation from GR.

 

 

Thalmann, C., Usuda, T., Kenworthy, M., Janson, M., Mamajek, E.E., Brandner, W., Dominik, C., Goto, M., Hayano, Y., Henning, T., Hinz, P.M., Minowa, Y., Tamura, M., 2011, "Piercing the Glare: A Direct Imaging Search for Planets in the Sirius System," The Astrophysical Journal, 732, L34.

 

       Astrometric monitoring of the Sirius binary system over the past century has yielded several predictions for an unseen third system component, the most recent one suggesting a lsim50 M Jup object in a ~6.3 year orbit around Sirius A. Here we present two epochs of high-contrast imaging observations performed with Subaru IRCS and AO188 in the 4.05 μm narrowband Br α filter. These data surpass previous observations by an order of magnitude in detectable companion mass, allowing us to probe the relevant separation range down to the planetary-mass regime (6-12 M Jup at 1'', 2-4 M Jup at 2'', and 1.6 M Jup beyond 4''). We complement these data with one epoch of M-band observations from MMT/AO Clio, which reach comparable performance. No data set reveals any companion candidates above the 5σ level, allowing us to refute the existence of Sirius C as suggested by the previous astrometric analysis. Furthermore, our Br α photometry of Sirius B confirms the lack of an infrared excess beyond the white dwarf's blackbody spectrum.

 

 

Tingley, B., 2011, "Searching for transits in data with long time baselines and poor sampling," Astronomy and Astrophysics, 529, 6.

 

       Aims: The standard method of searching parameter space for transits is ill-suited to data sets with long time baselines and poor temporal coverage, such as that anticipated from Gaia. In this paper, we present an alternative method for identifying transit candidates is such data, one focusing on finding periodicity in high S/N outliers. 

Methods: We describe a technique for testing a small number of flux measurements for periodicity and consistency with an origin in a transit with a constant change in flux and test their performance with Monte Carlo simulations. To complement this, we also include a description of a statistical method to analyze the distribution of these measurements to determine if they are normally distributed around a constant, reduce flux consistent with a planetary transits. 

Results: Large numbers of light curves can be quickly scanned for transit signatures with minimal loss in effectiveness for data sets with long time baselines and poor temporal coverage, where one observation per transit is the norm by testing for periodicity and analyzing their distribution. 

Conclusions: If the noise characteristics of the data set and the intrinsic noise of the individual stars are understood, this method focusing on statistical outliers is nearly equivalent to the standard method of scanning parameter space and significantly faster, if the signal ≫ noise, the individual transits are sampled no more than once and a periodicity test is employed. Moreover, the test for a transit origin can eliminate additional false positives.

 

 

Tinto, M., 2011, "Nanohertz Gravitational Wave Searches with Interferometric Pulsar Timing Experiments," Physical Review Letters, 106, 191101.

 

       We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same timekeeping subsystem (i.e., .the clock.). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band (10-9-10-8)Hz, this .interferometric. pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost 2 orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the NASA.s Deep Space Network and the forthcoming large arraying projects..

 

 

Watson, C.A., Littlefair, S.P., Diamond, C., Collier Cameron, A., Fitzsimmons, A., Simpson, E., Moulds, V., Pollacco, D., 2011, "On the alignment of debris discs and their host stars' rotation axis - implications for spin-orbit misalignment in exoplanetary systems," Monthly Notices of the Royal Astronomical Society, 413, L71-L75.

 

       It has been widely thought that measuring the misalignment angle between the orbital plane of a transiting exoplanet and the spin of its host star was a good discriminator between different migration processes for hot-Jupiters. Specifically, well-aligned hot-Jupiter systems (as measured by the Rossiter-McLaughlin effect) were thought to have formed via migration through interaction with a viscous disc, while misaligned systems were thought to have undergone a more violent dynamical history. These conclusions were based on the assumption that the planet-forming disc was well-aligned with the host star. Recent work by a number of authors has challenged this assumption by proposing mechanisms that act to drive the star-disc interaction out of alignment during the pre-main-sequence phase. We have estimated the stellar rotation axis of a sample of stars which host spatially resolved debris discs. Comparison of our derived stellar rotation axis inclination angles with the geometrically measured debris-disc inclinations shows no evidence for a misalignment between the two.

 

 

Williams, I.P., Ryabova, G.O., 2011, "Meteor shower features: are they governed by the initial formation process or by subsequent gravitational perturbations?," Monthly Notices of the Royal Astronomical Society, 910.

 

       The fine-structure properties found in a meteoroid stream determine what is observed in the associated meteor shower. These properties depend both on the ejection process of meteoroids from their parent body and on the subsequent orbital evolution which is determined by gravitational perturbations and radiation effects. Until about 30 years ago computing capabilities were not large enough to allow the integration of orbits of a significant number of meteoroids, therefore in practice it was impossible to combine an initial ejection process and follow the effects of perturbations. Computing capabilities have improved dramatically and the question of whether the structure that is present in streams today is determined primarily by the ejection process or by the subsequent orbital evolution can be considered. No single answer can be expected to the question that is the subject of our investigation. In some cases a structure introduced into the stream by the ejection process will survive to be observable today, in others it will not. We thus proceed by reviewing much of the previously published work that is relevant to this problem and we also produce some new results on the Geminid and Quadrantid streams.

 

 

Wyatt, M.C., Clarke, C.J., Booth, M., 2011, "Debris disk size distributions: steady state collisional evolution with Poynting-Robertson drag and other loss processes," Celestial Mechanics and Dynamical Astronomy, 24.

 

       We present a new scheme for determining the shape of the size distribution, and its evolution, for collisional cascades of planetesimals undergoing destructive collisions and loss processes like Poynting-Robertson drag. The scheme treats the steady state portion of the cascade by equating mass loss and gain in each size bin; the smallest particles are expected to reach steady state on their collision timescale, while larger particles retain their primordial distribution. For collision-dominated disks, steady state means that mass loss rates in logarithmic size bins are independent of size. This prescription reproduces the expected two phase size distribution, with ripples above the blow-out size, and above the transition to gravity-dominated planetesimal strength. The scheme also reproduces the expected evolution of disk mass, and of dust mass, but is computationally much faster than evolving distributions forward in time. For low-mass disks, P-R drag causes a turnover at small sizes to a size distribution that is set by the redistribution function (the mass distribution of fragments produced in collisions). Thus information about the redistribution function may be recovered by measuring the size distribution of particles undergoing loss by P-R drag, such as that traced by particles accreted onto Earth. Although cross-sectional area drops with age {∝ t-2} in the PR-dominated regime, dust mass falls {∝ t-2.8} , underlining the importance of understanding which particle sizes contribute to an observation when considering how disk detectability evolves. Other loss processes are readily incorporated; we also discuss generalised power law loss rates, dynamical depletion, realistic radiation forces and stellar wind drag.

 

 

Yardley, D.R.B., Coles, W.A., Hobbs, G.B., Verbiest, J.P.W., Manchester, R.N., van Straten, W., Jenet, F.A., Bailes, M., Bhat, N.D.R., Burke-Spolaor, S., Champion, D.J., Hotan, A.W., Oslowski, S., Reynolds, J.E., Sarkissian, J.M., 2011, "On detection of the stochastic gravitational-wave background using the Parkes pulsar timing array," Monthly Notices of the Royal Astronomical Society, 414, 1777-1787.

 

       We search for the signature of an isotropic stochastic gravitational-wave background in pulsar timing observations using a frequency-domain correlation technique. These observations, which span roughly 12 yr, were obtained with the 64-m Parkes radio telescope augmented by public domain observations from the Arecibo Observatory. A wide range of signal processing issues unique to pulsar timing and not previously presented in the literature are discussed. These include the effects of quadratic removal, irregular sampling and variable errors which exacerbate the spectral leakage inherent in estimating the steep red spectrum of the gravitational-wave background. These observations are found to be consistent with the null hypothesis that no gravitational-wave background is present, with 76 per cent confidence. We show that the detection statistic is dominated by the contributions of only a few pulsars because of the inhomogeneity of this data set. The issues of detecting the signature of a gravitational-wave background with future observations are discussed.

 

 

Zhao, W., 2011, "Constraint on the early Universe by relic gravitational waves: From pulsar timing observations," Physical Review D, 83, 104021.

 

Recent pulsar timing observations by the Parkers Pulsar Timing Array (PPTA) and European Pulsar Timing Array (EPTA) teams obtained the constraint on the relic gravitational waves at the frequency f*=1/yr, which provides the opportunity to constrain H*, the Hubble parameter, when these waves crossed the horizon during inflation. In this paper, we investigate this constraint by considering the general scenario for the early Universe: we assume that the effective (average) equation-of-state w before the big bang nucleosynthesis stage is a free parameter. In the standard hot big-bang scenario with w=1/3, we find that the current PPTA result follows a bound H*≤1.15×0-1mPl, and the EPTA result follows H*≤6.92×0-2mPl. We also find that these bounds become much tighter in the nonstandard scenarios with w>1/3. When w=1, the bounds become H*≤5.89×0-3mPl for the current PPTA and H*≤3.39×0-3mPl for the current EPTA. In contrast, in the nonstandard scenario with w=0, the bound becomes H*≤7.76mPl for the current PPTA.