tag:blogger.com,1999:blog-48226872351491043652024-03-08T10:20:20.334-08:00astro-ph.EP : Earth and Planetary AstrophysicsSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger2382125tag:blogger.com,1999:blog-4822687235149104365.post-30023890936384038982013-08-06T00:05:00.023-07:002013-08-06T00:05:17.256-07:001308.0599 (Dimitri Veras et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0599">An Exoplanet's Response to Anisotropic Stellar Mass-Loss During Birth
and Death</a> [<a href="http://arxiv.org/pdf/1308.0599">PDF</a>]</h2>Dimitri Veras, John D. Hadjidemetriou, Christopher A. Tout<a name='more'></a><blockquote class="abstract">The birth and death of planets may be affected by mass outflows from their parent stars during the T-Tauri or post-main-sequence phases of stellar evolution. These outflows are often modelled to be isotropic, but this assumption is not realistic for fast rotators, bipolar jets and supernovae. Here we derive the general equations of motion for the time evolution of a single planet, brown dwarf, comet or asteroid perturbed by anisotropic mass loss in terms of a complete set of planetary orbital elements, the ejecta velocity, and the parent star's co-latitude and longitude. We restrict our application of these equations to 1) rapidly rotating giant stars, and 2) arbitrarily-directed jet outflows. We conclude that the isotropic mass-loss assumption can safely be used to model planetary motion during giant branch phases of stellar evolution within distances of hundreds of au. In fact, latitudinal mass loss variations anisotropically affect planetary motion only if the mass loss is asymmetric about the stellar equator. Also, we demonstrate how constant-velocity, asymmetric bipolar outflows in young systems incite orbital inclination changes. Consequently, this phenomenon readily tilts exoplanetary orbits external to a nascent disc on the order of degrees.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0599">http://arxiv.org/abs/1308.0599</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-26416755477234155792013-08-06T00:05:00.021-07:002013-08-06T00:05:14.331-07:001308.0596 (Alex Dunhill et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0596">The curiously circular orbit of Kepler-16b</a> [<a href="http://arxiv.org/pdf/1308.0596">PDF</a>]</h2>Alex Dunhill, Richard Alexander<a name='more'></a><blockquote class="abstract">The recent discovery of a number of circumbinary planets lends a new tool to astrophysicists seeking to understand how and where planet formation takes place. Of the increasingly numerous circumbinary systems, Kepler-16 is arguably the most dynamically interesting: it consists of a planet on an almost perfectly circular orbit (e = 0.0069) around a moderately eccentric binary (e = 0.16). We present high-resolution 3D smoothed-particle hydrodynamics simulations of a Kepler-16 analogue embedded in a circumbinary disc, and show that the planet's eccentricity is damped by its interaction with the protoplanetary disc. We use this to place a lower limit on the gas surface density in the real disc through which Kepler-16b migrated of \Sigma_min ~ 10 g cm^-2. This suggests that Kepler-16b, and other circumbinary planets, formed and migrated in relatively massive discs. We argue that secular evolution of circumbinary discs requires that these planets likely formed early on in the lifetime of the disc and migrated inwards before the disc lost a significant amount of its original mass.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0596">http://arxiv.org/abs/1308.0596</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-63098476703738173182013-08-06T00:05:00.019-07:002013-08-06T00:05:13.432-07:001308.0607 (Rosemary A. Mardling)<h2 class="title"><a href="http://arxiv.org/abs/1308.0607">New developments for modern celestial mechanics. I. General coplanar
three-body systems. Application to exoplanets</a> [<a href="http://arxiv.org/pdf/1308.0607">PDF</a>]</h2>Rosemary A. Mardling<a name='more'></a><blockquote class="abstract">Modern applications of celestial mechanics include the study of closely packed systems of exoplanets, circumbinary planetary systems, binary-binary interactions in star clusters, and the dynamics of stars near the galactic centre. While developments have historically been guided by the architecture of the Solar System, the need for more general formulations with as few restrictions on the parameters as possible is obvious. Here we present clear and concise generalisations of two classic expansions of the three-body disturbing function, simplifying considerably their original form and making them accessible to the non-specialist. Governing the interaction between the inner and outer orbits of a hierarchical triple, the disturbing function in its general form is the conduit for energy and angular momentum exchange and as such, governs the secular and resonant evolution of the system and its stability characteristics. Focusing here on coplanar systems, the first expansion is one in the ratio of inner to outer semimajor axes and is valid for all eccentricities, while the second is an expansion in eccentricity and is valid for all semimajor axis ratios [...]. Our generalizations make both formulations valid for arbitrary mass ratios. [...]. We demonstrate the equivalence of the new expansions, identifying the role of the spherical harmonic order m in both and its physical significance in the three-body problem, and introducing the concept of principal resonances. Several examples of the accessibility of both expansions are given including resonance widths and the secular rates of change of the elements. Results in their final form are gathered together at the end of the paper for the reader mainly interested in their application, including a guide for the choice of expansion.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0607">http://arxiv.org/abs/1308.0607</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-74049665109723833012013-08-06T00:05:00.017-07:002013-08-06T00:05:12.742-07:001308.0616 (David Russell)<h2 class="title"><a href="http://arxiv.org/abs/1308.0616">A Proposal for New Definitions of Solar System Bodies - Planet, Moon,
and Satellite</a> [<a href="http://arxiv.org/pdf/1308.0616">PDF</a>]</h2>David Russell<a name='more'></a><blockquote class="abstract">A new classification system for Solar System bodies is proposed which takes into account both physical and dynamical perspectives as well as critiques of the IAU resolutions for the definitions of planet, dwarf planet, and small solar system bodies. In this proposal there are four classes of planets which correspond with environments of planetary formation in the early history of the Solar System: Terrestrial, Cerian, Jovian, and Kuiperian. Specific physical criteria are adopted for identifying an object as a planet and the four classes naturally address dynamical concerns. The proposal also addresses the problem of calling all satellites in the growing list of objects discovered orbiting the Jovian planets as moons by defining two classes of satellites: moons and satellites. Advantages of the new system over the current IAU definitions are discussed.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0616">http://arxiv.org/abs/1308.0616</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-40198700574634650422013-08-06T00:05:00.015-07:002013-08-06T00:05:11.792-07:001308.0629 (Jason W. Barnes et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0629">Measurement of Spin-Orbit Misalignment and Nodal Precession for the
Planet around Pre-Main-Sequence Star PTFO 8-8695 From Gravity Darkening</a> [<a href="http://arxiv.org/pdf/1308.0629">PDF</a>]</h2>Jason W. Barnes, Julian C. van Eyken, Brian K. Jackson, David R. Ciardi, Jonathan J. Fortney<a name='more'></a><blockquote class="abstract">PTFO 8-8695b represents the first transiting exoplanet candidate orbiting a pre-main-sequence star. We find that the unusual lightcurve shapes of PTFO 8-8695 can be explained by transits of a planet across an oblate, gravity-darkened stellar disk. We simultaneously and self-consistently fit two separate lightcurves observed in 2009 December and 2010 December. Our two self-consistent fits yield M_p = 3.0 M_Jup and M_p = 3.6 M_Jup for assumed stellar masses of M_* = 0.34 M_Sun and M_* = 0.44 M_Sun respectively. The two fits have precession periods of 293 days and 581 days. These mass determinations (consistent with previous upper limits) along with the strength of the gravity-darkened precessing model together validate PTFO 8-8695b as just the second Hot Jupiter known to orbit an M-dwarf. Our fits show a high degree of spin-orbit misalignment in the PTFO 8-8695 system: 69 +/- 2 or 73.1 +/- 0.5 degrees, in the two cases. The large misalignment is consistent with the hypothesis that planets become Hot Jupiters with random orbital plane alignments early in a system's lifetime. We predict that as a result of the highly misaligned, precessing system, the transits should disappear for months at a time over the course of the system's precession period. The precessing, gravity-darkened model also predicts other observable effects: changing orbit inclination that could be detected by radial velocity observations, changing stellar inclination that would manifest as varying v sin i, changing projected spin-orbit alignment that could be seen by the Rossiter-McLaughlin effect, changing transit shapes over the course of the precession, and differing lightcurves as a function of wavelength. Our measured planet radii of 1.64 R_Jup and 1.68 R_Jup in each case are consistent with a young, hydrogen-dominated planet that results from a hot-start formation mechanism.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0629">http://arxiv.org/abs/1308.0629</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-36201011048262497882013-08-06T00:05:00.013-07:002013-08-06T00:05:10.737-07:001308.0648 (Zhaohuan Zhu et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0648">Particle Concentration At Planet Induced Gap Edges and Vortices: I.
Inviscid 3-D Hydro Disks</a> [<a href="http://arxiv.org/pdf/1308.0648">PDF</a>]</h2>Zhaohuan Zhu, James M. Stone, Roman R. Rafikov, Xuening Bai<a name='more'></a><blockquote class="abstract">We perform a systematic study of the dynamics of dust particles in protoplanetary disks with embedded planets using global 2-D and 3-D inviscid hydrodynamic simulations. We implement Lagrangian particles into magnetohydrodynamic code Athena with cylindrical coordinates and explore the behavior of dust grains with sizes spanning more than 6 orders of magnitude --- from the well-coupled to decoupled limits. We find two distinct outcomes depending on the mass of the embedded planet, which is varied between 8 M_earth to 9 M_{J}. In the presence of a low mass planet (8 M_earth), two narrow gaps start to open in the gas on each side of the planet where the density waves shock. Although these gaps are quite shallow, they dramatically affect particle drift speed and cause significant, axisymmetric dust depletion near the planet. On the other hand, a more massive planet (>0.1 M_{J}) carves out a deeper gap with sharp edges, which are unstable to the formation of vortices that later merge into a single vortex. The vortex is intrinsically 2-dimensional without strong vertical motion, and it orbits around the central star at an almost Keplerian speed. Particles with a wide range of sizes are trapped and settle to the midplane in the vortex. Dust surface density inside the vortex can be increased by more than 100 in a non-axisymmetric fashion. For very big particles we find strong eccentricity excitation, in particular around the planet and in the vicinity of the mean motion resonances, facilitating gap opening there. Our results imply that in weakly turbulent protoplanetary disk regions (e.g. the "dead zone") dust particles with a very wide range of sizes can be trapped at gap edges and inside vortices induced by planets with mass smaller than M_{J}, potentially accelerating planetesimal and planet formation there, and giving rise to distinctive features that can be probed by ALMA and EVLA.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0648">http://arxiv.org/abs/1308.0648</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-30618553274340442292013-08-06T00:05:00.011-07:002013-08-06T00:05:09.974-07:001308.0825 (Farzana Meru et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0825">Growth and fragmentation of centimetre-sized dust aggregates: the
dependence on aggregate size and porosity</a> [<a href="http://arxiv.org/pdf/1308.0825">PDF</a>]</h2>Farzana Meru, Ralf J. Geretshauser, Christoph Schaefer, Roland Speith, Wilhelm Kley<a name='more'></a><blockquote class="abstract">We carry out three-dimensional Smoothed Particle Hydrodynamics simulations of spherical homogeneous SiO2 dust aggregates to investigate how the mass and the porosity of the aggregates affects their ability to survive an impact at various different collision velocities (between 1 - 27.5m/s). We explore how the threshold velocities for fragmentation vary with these parameters. Crucially, we find that the porosity plays a part of utmost importance in determining the outcome of collisions. In particular, we find that aggregates with filling factors >37% are significantly weakened and that the velocity regime in which the aggregates grow is reduced or even non-existent (instead, the aggregates either rebound off each other or break apart). At filling factors less than ~37% we find that more porous objects are weaker but not as weak as highly compact objects with filling factors >37%. In addition we find that (for a given aggregate density) collisions between very different mass objects have higher threshold velocities than those between very similar mass objects. We find that fragmentation velocities are higher than the typical values of 1m/s and that growth can even occur for velocities as high as 27.5m/s. Therefore, while the growth of aggregates is more likely if collisions between different sized objects occurs or if the aggregates are porous with filling factor <37%, it may also be hindered if the aggregates become too compact.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0825">http://arxiv.org/abs/1308.0825</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-50407437469566148122013-08-06T00:05:00.009-07:002013-08-06T00:05:09.024-07:001308.0882 (Ing-Guey Jiang et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0882">Investigating Close-in Exoplanets through Transit Observations</a> [<a href="http://arxiv.org/pdf/1308.0882">PDF</a>]</h2>Ing-Guey Jiang, Li-Chin Yeh, Parijat Thakur, Ping Chien, Yi-Ling Lin, Yu-Ting Wu, Hong-Yu Chen, Zhao Sun, Jianghui Ji<a name='more'></a><blockquote class="abstract">Through the international collaborators, we recently established a network of existing and working meter-class telescopes to look for planetary transit events. As a first step, we focus on the TrES3 system, and conclude that there could be some level of transit timing variations.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0882">http://arxiv.org/abs/1308.0882</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-15516138523774693472013-08-06T00:05:00.007-07:002013-08-06T00:05:08.259-07:001308.0899 (P. von Paris et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0899">The dependence of the ice-albedo feedback on atmospheric properties</a> [<a href="http://arxiv.org/pdf/1308.0899">PDF</a>]</h2>P. von Paris, F. Selsis, D. Kitzmann, H. Rauer<a name='more'></a><blockquote class="abstract">The ice-albedo feedback is a potentially important de-stabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) for this feedback. A plane-parallel radiative transfer model is used for the calculation of planetary albedos. We varied CO2 partial pressures as well as the H2O, CH4, and O3 content in the atmosphere for planets orbiting Sun-like and M-type stars. Results suggest that for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases can considerably change the strength of the ice-albedo feedback. For dense CO2 atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO2 pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H2O and CH4 in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O3 could also lead to a very strong decrease of the ice-albedo feedback at high CO2 pressures. (abridged)</blockquote>View original: <a href="http://arxiv.org/abs/1308.0899">http://arxiv.org/abs/1308.0899</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-29420141232495461342013-08-06T00:05:00.005-07:002013-08-06T00:05:07.202-07:001308.0921 (Thorben Kelling et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0921">Accretion through the inner edges of protoplanetary disks by a giant
solid state pump</a> [<a href="http://arxiv.org/pdf/1308.0921">PDF</a>]</h2>Thorben Kelling, Gerhard Wurm<a name='more'></a><blockquote class="abstract">At the inner edge of a protoplanetary disk solids are illuminated by stellar light. This illumination heats the solids and creates temperature gradients along their surfaces. Interactions with ambient gas molecules lead to a radial net gas flow. Every illuminated solid particle within the edge is an individual small gas pump transporting gas inward. In total the inner edge can provide local mass flow rates as high as $\dot{M} = 10^{-5} M_{\odot}$ yr$^{-1}$.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0921">http://arxiv.org/abs/1308.0921</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-11236404665122004092013-08-06T00:05:00.003-07:002013-08-06T00:05:06.549-07:001308.0996 (Yang Ming et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0996">Confirmation of 8 Planets in 4 Multi-planet Systems via TTVs in 1350
Days</a> [<a href="http://arxiv.org/pdf/1308.0996">PDF</a>]</h2>Yang Ming, Liu Hui-Gen, Zhang Hui, Zhou Ji-Lin<a name='more'></a><blockquote class="abstract">Analysis of the transit timing variations (TTVs) of candidate pairs near mean-motion resonances (MMRs) is an effective method to confirm planets. Hitherto, 66 planets in 33 multi-planet systems have been confirmed via TTVs. We analyse the TTVs of all candidates from the most recent {\it{Kepler}} data with a time span as long as about 1350 days (Q0-Q15). The anti-correlations and mass upper limits of candidate pairs in the same system are calculated, using an improved method suitable for long-period TTVs. If the flase alarm probabality (FAP) of a candidate pair is less than $10^{-3}$ and the mass upper limit for each candidate is less than 13 $M_{\rm J}$, we confirm them as planets in the same system. Finally, 8 planets in 4 multi-planet systems are confirmed via analysis of their TTVs. All of the 4 planet pairs are near first-order MMRs, including KOI-2672 near 2:1 MMR, KOI-1236, KOI-1563 and KOI-2038 near 3:2 MMR. Four planets have relatively long periods ($>$ 35 day). KOI-2672.01 has a period of 88.51658 day and a mass upper limit about $17.086 M_\oplus$. It is the second longest periodical planet confirmed via TTVs.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0996">http://arxiv.org/abs/1308.0996</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-29137963405023642212013-08-06T00:05:00.001-07:002013-08-06T00:05:05.729-07:001308.1058 (G. R. Mamatsashvili et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.1058">Revisiting linear dynamics of non-axisymmetric perturbations in weakly
magnetized accretion discs</a> [<a href="http://arxiv.org/pdf/1308.1058">PDF</a>]</h2>G. R. Mamatsashvili, G. D. Chagelishvili, G. Bodo, P. Rossi<a name='more'></a><blockquote class="abstract">We investigate linear dynamics of non-axisymmetric perturbations in incompressible, vertically stratified Keplerian discs with a weak vertical magnetic field in the shearing box approximation. Perturbations are decomposed into shearing waves whose evolution is followed via numerical integration of the linearized ideal MHD equations. There are two basic modes in the system -- inertia-gravity waves and magnetic mode, which displays the magnetorotational instability (MRI). As distinct from previous studies, we introduce `eigenvariables' characterizing each (counter-propagating) component of the inertia-gravity and magnetic modes, which are governed by a set of four first order coupled ordinary differential equations. This allowed us to identify a new process of linear coupling of the two above non-axisymmetric modes due to the disc's differential rotation. We did a comparative analysis of the dynamics of non-axisymmetric and axisymmetric magnetic mode perturbations. It is shown that the growth of optimal and close-to-optimal non-axisymmetric harmonics of this mode, having transient nature, can prevail over the exponential growth of axisymmetric ones (i.e., over the axisymmetric MRI) during dynamical time. A possible implication of this result for axisymmetric channel solutions is discussed. Specifically, the formation of the channel may be affected/impeded by non-axisymmetric modes already at the early linear stage leading to its untimely disruption -- the outcome strongly depends on the amplitude and spectrum of initial perturbation. So, this competition may result in an uncertainty in the magnetic mode's non-linear dynamics. It is also shown that a maximum non-axisymmetric growth is at vertical wavelengths close to the scale-height for which compressibility effects are important. This indirectly suggests that compressibility plays a role in the dynamics of the non-axisymmetric MRI.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1058">http://arxiv.org/abs/1308.1058</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-12168930531441080032013-08-05T00:04:00.013-07:002013-08-05T00:04:07.211-07:001308.0562 (S. Ueta et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0562">Structure of Surface-H2O Layers of Ice-covered Planets with
High-pressure Ice</a> [<a href="http://arxiv.org/pdf/1308.0562">PDF</a>]</h2>S. Ueta, T. Sasaki<a name='more'></a><blockquote class="abstract">Many extrasolar (bound) terrestrial planets and free-floating (unbound) planets have been discovered. The existence of bound and unbound terrestrial planets with liquid water is an important question, and of particular importance is the question of their habitability. Even for a globally ice-covered planet, geothermal heat from the planetary interior may melt the interior ice, creating an internal ocean covered by an ice shell. In this paper, we discuss the conditions that terrestrial planets must satisfy for such an internal ocean to exist on the timescale of planetary evolution. The question is addressed in terms of planetary mass, distance from a central star, water abundance, and abundance of radiogenic heat sources. In addition, we investigate the structures of the surface-H2O layers of ice-covered planets by considering the effects of ice under high pressure (high-pressure ice). As a fiducial case, 1M$\oplus$ planet at 1 AU from its central star and with 0.6 to 25 times the H2O mass of Earth could have an internal ocean. We find that high-pressure ice layers may appear between the internal ocean and the rock portion on a planet with an H2O mass over 25 times that of Earth. The planetary mass and abundance of surface water strongly restrict the conditions under which an extrasolar terrestrial planet may have an internal ocean with no high-pressure ice under the ocean. Such high-pressure-ice layers underlying the internal ocean are likely to affect the habitability of the planet.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0562">http://arxiv.org/abs/1308.0562</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-64506770278534102342013-08-05T00:04:00.011-07:002013-08-05T00:04:06.218-07:001308.0561 (Vincent Bourrier et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0561">3D model of hydrogen atmospheric escape from HD209458b and HD189733b:
radiative blow-out and stellar wind interactions</a> [<a href="http://arxiv.org/pdf/1308.0561">PDF</a>]</h2>Vincent Bourrier, Alain Lecavelier des Etangs<a name='more'></a><blockquote class="abstract">Transit observations in Ly-alpha of HD209458b and HD189733b revealed signatures of neutral hydrogen escaping the planets. We present a 3D particle model of the dynamics of the escaping atoms, and calculate theoretical Ly-alpha absorption line profiles, which can be directly compared with the absorption observed in the blue wing of the line. For HD209458b the observed velocities of the escaping atoms up to -130km/s are naturally explained by radiation-pressure acceleration. The observations are well-fitted with an ionizing flux of about 3-4 times solar and a hydrogen escape rate in the range 10^9-10^11g/s, in agreement with theoretical predictions. For HD189733b absorption by neutral hydrogen was observed in 2011 in the velocity range -230 to -140km/s. These velocities are higher than for HD209458b and require an additional acceleration mechanism for the escaping hydrogen atoms, which could be interactions with stellar wind protons. We constrain the stellar wind (temperature ~3x10^4K, velocity 200+-20km/s and density in the range 10^3-10^7/cm3) as well as the escape rate (4x10^8-10^11g/s) and ionizing flux (6-23 times solar). We also reveal the existence of an 'escape-limited' saturation regime in which most of the escaping gas interacts with the stellar protons. In this regime, which occurs at proton densities above ~3x10^5/cm3, the amplitude of the absorption signature is limited by the escape rate and does not depend on the wind density. The non-detection of escaping hydrogen in earlier observations in 2010 can be explained by the suppression of the stellar wind at that time, or an escape rate of about an order of magnitude lower than in 2011. For both planets, best-fit simulations show that the escaping atmosphere has the shape of a cometary tail.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0561">http://arxiv.org/abs/1308.0561</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-87903179669196042102013-08-05T00:04:00.009-07:002013-08-05T00:04:05.477-07:001308.0337 (D. Föhring et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0337">ULTRACAM z'-band Detection of the Secondary Eclipse of WASP-12b</a> [<a href="http://arxiv.org/pdf/1308.0337">PDF</a>]</h2>D. Föhring, V. S. Dhillon, Nikku Madhusudhan, T. R. Marsh, C. M. Copperwheat, S. P. Littlefair, Richard W. Wilson<a name='more'></a><blockquote class="abstract">We present z'-band secondary eclipse photometry of the highly irradiated hot Jupiter WASP-12b using ULTRACAM on the 4.2m William Herschel Telescope. We measure a decrease in flux of \delta = 0.130+/-0.013% during the passage of the planet behind the star, which is significantly deeper than the previous measurement at this wavelength (0.082+/-0.015%, L\'opez-Morales et al. 2010). Our secondary eclipse is best fit with a mid-eclipse phase, \phi, that is compatible with a circular orbit \phi = 0.501+/-0.002, in agreement with previous results (Croll et al. 2011). In combination with existing data, our eclipse depth measurement allows us to constrain the characteristics of the planet's atmosphere, which is consistent with a carbon-rich model, with no evidence for a strong thermal inversion. If the difference in eclipse depth reported here compared to that of L\'opez-Morales et al. (2010) is of physical origin, as opposed to due to systematics, it may be caused by temporal variability in the flux, due to atmospheric dynamics.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0337">http://arxiv.org/abs/1308.0337</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-12212048780180038022013-08-05T00:04:00.007-07:002013-08-05T00:04:04.766-07:001308.0373 (A. Hees et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0373">How to test SME with space missions ?</a> [<a href="http://arxiv.org/pdf/1308.0373">PDF</a>]</h2>A. Hees, B. Lamine, C. Le Poncin-Lafitte, P. Wolf<a name='more'></a><blockquote class="abstract">In this communication, we focus on possibilities to constrain SME coefficients using Cassini and Messenger data. We present simulations of radioscience observables within the framework of the SME, identify the linear combinations of SME coefficients the observations depend on and determine the sensitivity of these measurements to the SME coefficients. We show that these datasets are very powerful for constraining SME coefficients.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0373">http://arxiv.org/abs/1308.0373</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-73661046049919131042013-08-05T00:04:00.005-07:002013-08-05T00:04:04.054-07:001308.0446 (J. Hanuš et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0446">Sizes of main-belt asteroids by combining shape models and Keck adaptive
aptics observations</a> [<a href="http://arxiv.org/pdf/1308.0446">PDF</a>]</h2>J. Hanuš, F. Marchis, J. Ďurech<a name='more'></a><blockquote class="abstract">We select 50 main-belt asteroids with a diameter between 20 and 400 km for which we have (i) shape models derived by the lightcurve inversion method (LI) and (ii) resolved observations of good quality collected with the Keck II adaptive optics (AO) system in the near-infrared. We derive the size of these asteroids by minimizing the difference between the contours from deconvolved AO images and the projected silhouettes calculated from the shape model at the time of the AO observations. We compute the volume-equivalent diameters for 48 of these asteroids. For 15 of them, we remove the ambiguity of the pole orientation typical for shape models derived by the LI. We have found that our equivalent diameters are smaller by 3%, 7%, and 2% compared with the effective diameters derived from mid-IR photometric observations provided by IRAS, WISE and AKARI. For 40 asteroids with previously determined mass estimates, we compute their bulk densities and discuss the mass-density dependence with respect to taxonomic types.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0446">http://arxiv.org/abs/1308.0446</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-33904452989168809672013-08-05T00:04:00.003-07:002013-08-05T00:04:03.386-07:001308.0511 (F. Tian)<h2 class="title"><a href="http://arxiv.org/abs/1308.0511">Conservation of Total Escape from Hydrodynamic Planetary Atmospheres</a> [<a href="http://arxiv.org/pdf/1308.0511">PDF</a>]</h2>F. Tian<a name='more'></a><blockquote class="abstract">Atmosphere escape is one key process controlling the evolution of planets. However, estimating the escape rate in any detail is difficult because there are many physical processes contributing to the total escape rate. Here we show that as a result of energy conservation the total escape rate from hydrodynamic planetary atmospheres where the outflow remains subsonic is nearly constant under the same stellar XUV photon flux when increasing the escape efficiency from the exobase level, consistent with the energy limited escape approximation. Thus the estimate of atmospheric escape in a planet's evolution history can be greatly simplified.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0511">http://arxiv.org/abs/1308.0511</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-83258823090896323402013-08-05T00:04:00.001-07:002013-08-05T00:04:00.419-07:001308.0563 (Malgorzata Krolikowska et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0563">Near-parabolic comets observed in 2006-2010. The individualized approach
to 1/a-determination and the new distribution of original and future orbits</a> [<a href="http://arxiv.org/pdf/1308.0563">PDF</a>]</h2>Malgorzata Krolikowska, Piotr A. Dybczynski<a name='more'></a><blockquote class="abstract">Dynamics of a complete sample of 22 small perihelion distance near-parabolic comets discovered in the years 2006 - 2010 is studied. First, osculating orbits are obtained after a careful positional data inspection and processing, including where appropriate, the method of data partitioning for determination of pre- and post-perihelion orbit for tracking then its dynamical evolution. The nongravitational acceleration in the motion is detected for 50 per cent of investigated comets, in a few cases for the first time. Different sets of nongravitational parameters are determined from pre- and post-perihelion data for some of them. The influence of the positional data structure on the possibility of the detection of nongravitational effects and the overall precision of orbit determination is widely discussed. Secondly, both original and future orbits were derived by means of numerical integration of swarms of virtual comets obtained using a Monte Carlo cloning method. This method allows to follow the uncertainties of orbital elements at each step of dynamical evolution. The complete statistics of original and future orbits that includes significantly different uncertainties of 1/a-values is presented, also in the light of our results obtained earlier. Basing on 108 comets examined by us so far, we conclude that only one of them, C/2007 W1 Boattini, seems to be a serious candidate for an interstellar comet. We also found that 53 per cent of 108 near-parabolic comets escaping in the future from the Solar system, and the number of comets leaving the Solar system as so called Oort spike comets is 14 per cent. A new method for cometary orbit quality assessment is also proposed that leads to a better diversification of orbit quality classes for contemporary comets.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0563">http://arxiv.org/abs/1308.0563</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-29796511163397239862013-08-05T00:03:00.001-07:002013-08-05T00:03:59.386-07:001308.0571 (J. M. Madiedo et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0571">Spectroscopy and Orbital Analysis of Bright Bolides Observed over the
Iberian Peninsula from 2010 to 2012</a> [<a href="http://arxiv.org/pdf/1308.0571">PDF</a>]</h2>J. M. Madiedo, J. M. Trigo-Rodriguez, J. L. Ortiz, A. J. Castro-Tirado, S. Pastor, J. A. de los Reyes, J. Cabrera-Cano<a name='more'></a><blockquote class="abstract">We present the analysis of the atmospheric trajectory and orbital data of four bright bolides observed over Spain, one of which is a potential meteorite dropping event. Their absolute magnitude ranges from -10 to -11. Two of these are of sporadic origin, although a Geminid and a kappa-Cygnid fireball are also considered. These events were recorded in the framework of the continuous fireball monitoring and spectroscopy campaigns developed by the SPanish Meteor Network (SPMN) between 2010 and 2012. The tensile strength of the parent meteoroids is estimated and the abundances of the main rock-forming elements in these particles are calculated from the emission spectrum obtained for three of these events. This analysis revealed a chondritic nature for these meteoroids.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0571">http://arxiv.org/abs/1308.0571</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-47694034744645102162013-08-04T00:06:00.011-07:002013-08-04T00:06:18.539-07:001308.0009 (David M. Kipping)<h2 class="title"><a href="http://arxiv.org/abs/1308.0009">Efficient, uninformative sampling of limb darkening coefficients for
two-parameter laws</a> [<a href="http://arxiv.org/pdf/1308.0009">PDF</a>]</h2>David M. Kipping<a name='more'></a><blockquote class="abstract">Stellar limb darkening affects a wide range of astronomical measurements and is frequently modeled with a parametric model using polynomials in the cosine of the angle between the line of sight and the emergent intensity. Two-parameter laws are particularly popular for cases where one wishes to fit freely for the limb darkening coefficients (i.e. an uninformative prior) due to the compact prior volume and the fact more complex models rarely obtain unique solutions with present data. In such cases, we show that the two limb darkening coefficients are constrained by three physical boundary conditions, describing a triangular region in the two-dimensional parameter space. We show that uniformly distributed samples may be drawn from this region with optimal efficiency by a technique developed by computer graphical programming: triangular sampling. Alternatively, one can use make draws using a uniform, bivariate Dirichlet distribution. We provide simple expressions for these parametrizations for both techniques applied to the case of quadratic, square-root and logarithmic limb darkening laws. For example, in the case of the popular quadratic law, we advocate fitting for q_1 = (u_1+u_2)^2 and q_2 = 0.5u_1(u_1+u_2)^{-1} with uniform priors in the interval [0,1] to implement triangular sampling easily. Employing these parametrizations allows one to derive model parameters which fully account for our ignorance about the intensity profile, yet never explore unphysical solutions, yielding robust and realistic uncertainty estimates. Furthermore, in the case of triangular sampling with the quadratic law, our parametrization leads to significantly reduced mutual correlations and provides an alternative geometric explanation as to why naively fitting the quadratic limb darkening coefficients precipitates strong correlations in the first place.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0009">http://arxiv.org/abs/1308.0009</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-8228118725027202542013-08-04T00:06:00.009-07:002013-08-04T00:06:16.698-07:001308.0014 (R. E. Pike et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0014">On a Possible Size/Color Relationship in the Kuiper Belt</a> [<a href="http://arxiv.org/pdf/1308.0014">PDF</a>]</h2>R. E. Pike, J. J. Kavelaars<a name='more'></a><blockquote class="abstract">Color measurements and albedo distributions introduce non-intuitive observational biases in size-color relationships among Kuiper Belt Objects (KBOs) that cannot be disentangled without a well characterized sample population with systematic photometry. Peixinho et al. report that the form of the KBO color distribution varies with absolute magnitude, H. However, Tegler et al. find that KBO color distributions are a property of object classification. We construct synthetic models of observed KBO colors based on two B-R color distribution scenarios: color distribution dependent on H magnitude (H-Model) and color distribution based on object classification (Class-Model). These synthetic B-R color distributions were modified to account for observational flux biases. We compare our synthetic B-R distributions to the observed 'Hot' and 'Cold' detected objects from the Canada-France Ecliptic Plane Survey and the Meudon Multicolor Survey. For both surveys, the Hot population color distribution rejects the H-Model, but is well described by the Class-Model. The Cold objects reject the H-Model, but the Class-Model (while not statistically rejected) also does not provide a compelling match for data. Although we formally reject models where the structure of the color distribution is a strong function of H magnitude, we also do not find that a simple dependence of color distribution on orbit classification is sufficient to describe the color distribution of classical KBOs.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0014">http://arxiv.org/abs/1308.0014</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-16580998576901087352013-08-04T00:06:00.007-07:002013-08-04T00:06:15.189-07:001308.0016 (Ryan M. O'Leary et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0016">It takes a village to raise a tide: nonlinear multiple-mode coupling and
mode identification in KOI-54</a> [<a href="http://arxiv.org/pdf/1308.0016">PDF</a>]</h2>Ryan M. O'Leary, Joshua Burkart<a name='more'></a><blockquote class="abstract">We explore the tidal excitation of stellar modes in binary systems using Kepler observations of the remarkable eccentric binary KOI-54 (HD 187091; KIC 8112039), which displays strong ellipsoidal variation as well as a variety of linear and nonlinear pulsations. We report the amplitude and phase of over 120 harmonic and anharmonic pulsations in the system. We use pulsation phases to determine that the two largest-amplitude pulsations, the 90th and 91st harmonics, most likely correspond to axisymmetric m=0 modes in both stars, and thus cannot be responsible for resonance locks as had been recently proposed. We find evidence that the amplitude of at least one of these two pulsations is decreasing with a characteristic timescale of ~100 yr. We also use the pulsations' phases to confirm the onset of the traveling wave regime for harmonic pulsations with frequencies <~50 Omega_orbit, in agreement with theoretical expectations. We present evidence that many pulsations that are not harmonics of the orbital frequency correspond to modes undergoing simultaneous nonlinear coupling to multiple linearly driven parent modes. Since coupling among multiple modes can lower the threshold for nonlinear interactions, nonlinear phenomena may be easier to observe in highly eccentric systems, where broader arrays of driving frequencies are available. This may help to explain why the observed amplitudes of the linear pulsations are much smaller than the theoretical threshold for decay via three-mode coupling.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0016">http://arxiv.org/abs/1308.0016</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-8893434026049681822013-08-04T00:06:00.005-07:002013-08-04T00:06:11.673-07:001308.0114 (Aurora Sicilia-Aguilar et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0114">The low-mass stellar population in the young cluster Tr37: Disk
evolution, accretion, and environment</a> [<a href="http://arxiv.org/pdf/1308.0114">PDF</a>]</h2>Aurora Sicilia-Aguilar, Jinyoung Serena Kim, Andrej Sobolev, Konstantin Getman, Thomas Henning, Min Fang<a name='more'></a><blockquote class="abstract">We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr37. With a well-studied solar-type population, Tr37 is a benchmark for disk evolution. We used low-resolution spectroscopy to identify 141 members (78 new) and 64 probable members, mostly M-type stars. H\alpha\ emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the SEDs. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Including the new and previously known members, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr37 (4 Myr) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr), suggesting that other factors, like the environment/interactions, are likely to play a role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation or mini-clusters within Tr37.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0114">http://arxiv.org/abs/1308.0114</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-4822687235149104365.post-59341583066596639092013-08-04T00:06:00.003-07:002013-08-04T00:06:10.949-07:001308.0190 (N. V. Erkaev et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0190">Escape of the martian protoatmosphere and initial water inventory</a> [<a href="http://arxiv.org/pdf/1308.0190">PDF</a>]</h2>N. V. Erkaev, H. Lammer, L. Elkins-Tanton, A. Stökl, P. Odert, E. Marcq, E. A. Dorfi, K. G. Kislyakova, Yu. N. Kulikov, M. Leitzinger, M. Güdel<a name='more'></a><blockquote class="abstract">Latest research in planet formation indicate that Mars formed within a few million years (Myr) and remained a planetary embryo that never grew to a more massive planet. It can also be expected from dynamical models, that most of Mars' building blocks consisted of material that formed in orbital locations just beyond the ice line which could have contained ~0.1-0.2 wt. % of H2O. By using these constraints, we estimate the nebula-captured and catastrophically outgassed volatile contents during the solidification of Mars' magma ocean and apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere during the early active epoch of the young Sun. The amount of gas that has been captured from the protoplanetary disk into the planetary atmosphere is calculated by solving the hydrostatic structure equations in the protoplanetary nebula. Depending on nebular properties such as the dust grain depletion factor, planetesimal accretion rates and luminosities, hydrogen envelopes with masses >=3x10^{19} g to <=6.5x10^{22} g could have been captured from the nebula around early Mars. Depending of the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was ~100 times stronger compared to the present value, our results indicate that early Mars would have lost its nebular captured hydrogen envelope after the nebula gas evaporated, during a fast period of ~0.1-7.5 Myr. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of ~50-250 bar H2O and ~10-55 bar CO2 could have been lost during ~0.4-12 Myr, if the impact related energy flux of large planetesimals and small embryos to the planet's surface lasted long enough, that the steam atmosphere could have been prevented from condensing. If this was not the case... (continued)</blockquote>View original: <a href="http://arxiv.org/abs/1308.0190">http://arxiv.org/abs/1308.0190</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0