* Astronomy

Blobrana · L

Hot Jupiter atmospheres

Blobrana · L

RE: Hot Jupiters

Blobrana · L

Title: A paucity of proto-hot Jupiters on super-eccentric orbits
Authors: Rebekah I. Dawson, Ruth A. Murray-Clay, John Asher Johnson

Gas giant planets orbiting within 0.1 AU of their host stars, unlikely to have formed in situ, are evidence for planetary migration. It is debated whether the typical hot Jupiter smoothly migrated inward from its formation location through the proto-planetary disk or was perturbed by another body onto a highly eccentric orbit, which tidal dissipation subsequently shrank and circularised during close stellar passages. Socrates and collaborators predicted that the latter class of model should produce a population of super-eccentric proto-hot Jupiters readily observable by Kepler. We find a paucity of such planets in the Kepler sample, disagreeing with the theoretical prediction with 98.7% confidence. Observational effects are unlikely to explain this discrepancy. We find that the fraction of hot Jupiters with orbital period P > 3 days produced by the stellar binary Kozai mechanism does not exceed 0.15 +0.29/-0.11. Our results may indicate that disk migration is the dominant channel for producing hot Jupiters with P > 3 days. Alternatively, the typical hot Jupiter may have been perturbed to a high eccentricity by interactions with a planetary rather than stellar companion and began tidal circularisation much interior to the ice line after multiple scatterings. A final alternative is that tidal circularisation occurs much more rapidly early in the tidal circularisation process at high eccentricities than later in the process at low eccentricities, contrary to current tidal theories.

Read more (2075kb, PDF)

Blobrana · L

Title: Atmospheric circulation of hot Jupiters: insensitivity to initial conditions
Authors: Beibei Liu, Adam P. Showman

The ongoing characterisation of hot Jupiters has motivated a variety of circulation models of their atmospheres. Such models must be integrated starting from an assumed initial state, which is typically taken to be a wind-free, rest state. Here, we investigate the sensitivity of hot-Jupiter atmospheric circulation models to initial conditions. We consider two classes of models---shallow-water models, which have proven successful at illuminating the dynamical mechanisms at play on these planets, and full three-dimensional models similar to those being explored in the literature. Models are initialised with zonal jets, and we explore a variety of different initial jet profiles. We demonstrate that, in both classes of models, the final, equilibrated state is independent of initial condition. Otherwise identical models initialised with vastly different initial conditions all converge to the same statistical steady state. In some cases, the models exhibit modest time variability; this variability results in random fluctuations about the statistical steady state, but we emphasise that, even in these cases, the statistical steady state itself does not depend on initial conditions. Although the outcome of hot-Jupiter circulation models depend on details of the radiative forcing and frictional drag, aspects of which remain uncertain, we conclude that the specification of initial conditions is not a source of uncertainty, at least over the parameter range explored in most current models.

Read more (3181kb, PDF)

Blobrana · L

Title: Effects of Collisions with Rocky Planets on the Properties of Hot Jupiters
Authors: Kassandra R. Anderson, Fred C. Adams

Observed Hot Jupiters exhibit a wide range of physical properties. For a given mass, many planets have inflated radii, while others are surprisingly compact and may harbour large central cores. Motivated by the observational sample, this paper considers possible effects from collisions of smaller rocky planets with gas giant planets. In this scenario, the Jovian planets migrate first and enter into (approximately) 4 day orbits, whereas rocky planets (mass = 0.1-20 that of Earth) migrate later and then encounter the gaseous giants. Previous work indicates that the collision rates are high for such systems. This paper calculates the trajectories of incoming rocky planets as they orbit within the gaseous planets and are subjected to gravitational, frictional, and tidal forces. These collisions always increase the metallicity of the Jovian planets. If the incoming rocky bodies survive tidal destruction and reach the central regions, they provide a means of producing large planetary cores. Both the added metallicity and larger cores act to decrease the radii of the gas giants at fixed mass. The energy released during these collisions provides the Jovian planet with an additional heat source; here we determine the radial layers where kinetic energy of the colliding body is dissipated, including the energy remaining upon impact with the existing core. This process could have long-term effects if the colliding body deposits significant energy deep in the interior, in regions of high opacity. Both Hot Jupiters and newly formed gas giants have inflated radii, large enough to allow incoming rocky planets to survive tidal disruption, enhance the central core mass, and deposit significant energy (in contrast, denser giant planets with the mass and radius of Jupiter are expected to tidally destroy incoming rocky bodies).

Read more (1636kb, PDF)

Blobrana · L

Title: On the Formation of Hot Jupiters in Stellar Binaries
Authors: Smadar Naoz, Will M. Farr, Frederic A. Rasio

We study the production of Hot Jupiters (HJs) in stellar binaries. We show that the "eccentric Kozai-Lidov" (EKL) mechanism can play a key role in the dynamical evolution of a star-planet-star triple system. We run a large set of Monte Carlo simulations including the secular evolution of the orbits, general relativistic precession, and tides, and we determine the semi-major axis, eccentricity, inclination and spin-orbit angle distributions of the HJs that are produced. We explore the effect of different tidal friction parameters on the results. We find that the efficiency of forming HJs when taking the EKL mechanism into account is higher then previously estimated. Accounting for the frequency of stellar binaries, we find that this production mechanism can account for about 30% of the observed HJ population. Current observations of spin-orbit angles are consistent with this mechanism producing ~30% of all HJs, and up to 100% of the misaligned systems. Based on the properties of binaries without a HJ in our simulations, we predict the existence of many Jupiter-like planets with moderately eccentric and inclined orbits and semi-major axes of several AU.

Read more (103kb, PDF)

Blobrana · L

Title: The Frequency of Hot Jupiters Orbiting Nearby Solar-Type Stars
Authors: J. T. Wright, G. W. Marcy, A. W. Howard, John Asher Johnson, T. Morton, D. A. Fischer

We determine the fraction of F, G, and K dwarfs in the Solar Neighbourhood hosting hot jupiters as measured by the California Planet Survey from the Lick and Keck planet searches. We find the rate to be 1.2\pm0.38%, which is consistent with the rate reported by Mayor et al. (2011) from the HARPS and CORALIE radial velocity surveys. These numbers are more than double the rate reported by Howard et al. (2011) for Kepler stars and the rate of Gould et al. (2006) from the OGLE-III transit search, however due to small number statistics these differences are of only marginal statistical significance. We explore some of the difficulties in estimating this rate from the existing radial velocity data sets and comparing radial velocity rates to rates from other techniques.

Read more (15kb, PDF)

Blobrana · L

Title: Kepler constraints on planets near hot Jupiters
Authors: Jason H. Steffen (1), Darin Ragozzine (2), Daniel C. Fabrycky (3), Joshua A. Carter (2), Eric B. Ford (4), Matthew J. Holman (2), Jason F. Rowe (5), William F. Welsh (6), William J. Borucki (5), Alan P. Boss (7), David R. Ciardi (8), Samuel N. Quinn (2) ((1) Fermilab Center for Particle Astrophysics, (2) Harvard-Smithsonian Center for Astrophysics, (3) Department of Astronomy and Astrophysics, University of California, (4) Astronomy Department, University of Florida, (5) NASA Ames Research Centre, (6) Astronomy Department, San Diego State University, (7) Department of Terrestrial Magnetism Carnegie Institution for Science, (8) NASA Exoplanet Science Institute/California Institute of Technology)

We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 days) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 2:1 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly 2/3 to 5 times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations or TTVs) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history.

Read more (644kb, PDF)

Blobrana · L

Some giant planets in other systems most likely to be alone

"Hot Jupiter-type" planets are most likely to be alone in their systems, according to research by a University of Florida astronomer and others, made public today.
"Hot Jupiters" are giant planets beyond our solar system, roughly the size of Jupiter but orbiting close to their parent stars and thus much hotter than the Earth or Jupiter, said UF professor Eric Ford. They have very short orbital periods, completing a turn around their stars in fewer than 10 days. This study, published in the journal Proceedings of the National Academy of Sciences, provides new insights into how they are formed.
Read more

Blobrana · L

Title: Seven transiting hot-Jupiters from WASP-South, Euler and TRAPPIST: WASP-47b, WASP-55b, WASP-61b, WASP-62b, WASP-63b, WASP-66b & WASP-67b
Authors: Coel Hellier, D. R. Anderson, A. Collier Cameron, A. P. Doyle, M. Gillon, E. Jehin, M. Lendl, P. F. L. Maxted, F. Pepe, D. Pollacco, D. Queloz, D. Segransan, B. Smalley, A. M. S. Smith, J. Southworth, A. H. M. J. Triaud, S. Udry, R. G. West

We present seven new transiting hot Jupiters from the WASP-South survey. The planets are all typical hot Jupiters orbiting stars from F4 to K0 with magnitudes of V = 10.3 to 12.5. The orbital periods are all in the range 3.9--4.6 d, the planetary masses range from 0.4--2.3 Mjup and the radii from 1.1--1.4 Mjup. In line with known hot Jupiters, the planetary densities range from Jupiter-like to inflated (rho = 0.13--1.07 rho_jup). We use the increasing numbers of known hot Jupiters to investigate the distribution of their orbital periods and the 3--4-d "pile-up".

Read more (713kb, PDF)