* Astronomy

Blobrana · L

RE: Hot Jupiters

Blobrana · L

Title: C/O and O/H Ratios Suggest Some Hot Jupiters Originate Beyond the Snow Line
Author: John M. Brewer, Debra A. Fischer, Nikku Madhusudhan

The elemental compositions of planet hosting stars serve as proxies for the primordial compositions of the protoplanetary disks within which the planets form. The temperature profile of the disk governs the condensation fronts of various compounds, and although these chemically distinct regions migrate and mix during the disk lifetime, they can still leave an imprint on the compositions of the forming planets. Observable atmospheric compositions of hot Jupiters when compared against their host stars could potentially constrain their formation and migration processes. We compared the measured planetary and stellar abundances of carbon and oxygen for ten systems with hot Jupiters. If the planets formed by core accretion with significant planetesimal accretion and migrated through the disk, the hot Jupiter atmospheres should be substantially super-stellar in O/H and sub-stellar in C/O. On the contrary, however, we find that currently reported abundances of hot Jupiters have generally super-stellar C/O ratios, though present uncertainties on the reported O/H and C/O ratios are too large to reach a firm conclusion. In one case however, HD 209458b, the elevated C/O and depleted O/H of the planet compared to the host star is significant enough to suggest an origin far beyond the ice line, with predominantly gas accretion, and subsequent disk-free migration. Improved measurements from the James Webb Space Telescope will enable more precise measurements for more hot Jupiters and we predict, based on the current marginal trend, that a sizeable fraction of hot Jupiters will show enrichment of C/O and lower O/H than their hosts, similar to HD 209458b.

Read more (212kb, PDF)

Blobrana · L

Cloudy Nights, Sunny Days on Distant Hot Jupiters

The weather forecast for faraway, blistering planets called "hot Jupiters" might go something like this: Cloudy nights and sunny days, with a high of about 1,300 degrees Celsius, or 1,600 Kelvin.
These mysterious worlds are too far away for us to see clouds in their atmospheres. But a recent study using NASA's Kepler space telescope and computer modeling techniques finds clues to where such clouds might gather and what they're likely made of.
Read more

Blobrana · L

Title: A hot Jupiter for breakfast? --- Early stellar ingestion of planets may be common
Author: Titos Matsakos, Arieh Königl

Models of planet formation and evolution predict that giant planets form efficiently in protoplanetary disks, that most of these migrate rapidly to the disk's inner edge, and that, if the arriving planet's mass is \lesssim Jupiter's mass, it could remain stranded near that radius. We argue that such planets would be ingested by tidal interaction with the host star on a timescale \lesssim 1Gyr, and that, in the case of a solar-type host, this would cause the stellar spin to approach the direction of the ingested planet's orbital axis even if the two were initially highly misaligned. Primordially misaligned stars whose effective temperatures are \gtrsim 6250K cannot be realigned in this way because, in contrast with solar-type hosts, their angular momenta are typically higher than the orbital angular momentum of the ingested planet as a result of inefficient magnetic braking and of a comparatively large moment of inertia. Hot Jupiters located farther out from the star can contribute to this process, but their effect is weaker because the tidal interaction strength decreases rapidly with increasing semimajor axis. We demonstrate that, if ~50% of planetary systems harboured a stranded hot Jupiter, this scenario can in principle account for (1) the good alignment exhibited by planets around cool stars irrespective of the planet's mass or orbital period, (2) the prevalence of misaligned planets around hot stars, (3) the apparent upper bound on the mass of hot Jupiters on retrograde orbits, and (4) the inverse correlation between stellar spin periods and hot-Jupiter masses.

Read more (63kb, PDF)

Blobrana · L

Hot Jupiter exoplanets

Blobrana · L

RE: Hot Jupiters

Blobrana · L

Title: Planets on the Edge
Author: Francesca Valsecchi, Frederic A. Rasio

Hot Jupiters formed through circularization of high-eccentricity orbits should be found at orbital separations a exceeding twice that of their Roche limit aR. Nevertheless, about a dozen giant planets have now been found well within this limit (aR<a<2aR), with one coming as close as 1.2aR. In this Letter, we show that orbital decay (starting beyond 2aR) driven by tidal dissipation in the star can naturally explain these objects. For a few systems (WASP-4 and 19), this explanation requires the linear reduction in convective tidal dissipation proposed originally by Zahn (1966) and verified by recent numerical simulations (Penev et al. 2007), but rules out the quadratic prescription proposed by Goldreich and Nicholson (1977). Additionally, we find that WASP-19-type systems could potentially provide empirical support to the Zahn's (1966) prescription through high precision transit timing measurements of their orbital decay rate.

Read more (853kb, PDF)

Blobrana · L

The Strange Attraction of Hot Jupiters

When the Space Age began, astronomers knew of exactly zero planets outside the solar system. What a difference 50 years makes.Modern, ground-based telescopes and NASA's Kepler spacecraft have now confirmed more than 850 exoplanets, while thousands more await confirmation.

Blobrana · L

Title: Evidence for the Tidal Destruction of Hot Jupiters by Subgiant Stars
Authors: Kevin C. Schlaufman, Joshua N. Winn

Tidal transfer of angular momentum is expected to cause hot Jupiters to spiral into their host stars. Although the timescale for orbital decay is very uncertain, it should be faster for systems with larger and more evolved stars. Indeed, it is well established that hot Jupiters are found less frequently around subgiant stars than around main-sequence stars. However, the interpretation of this finding has been ambiguous, because the subgiants are also thought to be more massive than the F- and G-type stars that dominate the main-sequence sample. Consequently it has been unclear whether the absence of hot Jupiters is due to tidal destruction, or inhibited formation of those planets around massive stars. Here we show that the Galactic space motions of the planet-hosting subgiant stars demand that on average they be similar in mass to the planet-hosting main-sequence F- and G-type stars. Therefore the two samples are likely to differ only in age, and provide a glimpse of the same exoplanet population both before and after tidal evolution. As a result, the lack of hot Jupiters orbiting subgiants is clear evidence for their tidal destruction. Questions remain, though, about the interpretation of other reported differences between the planet populations around subgiants and main-sequence stars, such as their period and eccentricity distributions and overall occurrence rates.

Read more (415kb, PDF)

Blobrana · L

Title: Warm Spitzer Photometry of Three Hot Jupiters: HAT-P-3b, HAT-P-4b and HAT-P-12b
Authors: Kamen O. Todorov, Drake Deming, Heather A. Knutson, Adam Burrows, Jonathan J. Fortney, Nikole K. Lewis, Nicolas B. Cowan, Eric Agol, Jean-Michel Desert, Pedro V. Sada, David Charbonneau, Gregory Laughlin, Jonathan Langton, Adam P. Showman

We present Warm Spitzer/IRAC secondary eclipse time series photometry of three short-period transiting exoplanets, HAT-P-3b, HAT-P-4b and HAT-P-12b, in both the available 3.6 and 4.5 micron bands. HAT-P-3b and HAT-P-4b are Jupiter-mass, objects orbiting an early K and an early G dwarf stars, respectively. For HAT-P-3b we find eclipse depths of 0.112%+0.015%-0.030% (3.6 micron) and 0.094%+0.016%-0.009% (4.5 micron). The HAT-P-4b values are 0.142%+0.014%-0.016% (3.6 micron) and 0.122%+0.012%-0.014% (4.5micron). The two planets' photometry is consistent with inefficient heat redistribution from their day to night sides (and low albedos), but it is inconclusive about possible temperature inversions in their atmospheres. HAT-P-12b is a Saturn-mass planet and is one of the coolest planets ever observed during secondary eclipse, along with hot Neptune GJ 436b and hot Saturn WASP-29b. We are able to place 3\sigma upper limits on the secondary eclipse depth of HAT-P-12b in both wavelengths: < 0.042% (3.6 micron) and <0.085% (4.5 micron). We discuss these results in the context of the Spitzer secondary eclipse measurements of GJ 436b and WASP-29b. It is possible that we do not detect the eclipses of HAT-P-12b due to high eccentricity, but find that weak planetary emission in these wavelengths is a more likely explanation. We place 3 sigma upper limits on the |e cos(omega)| quantity (where e is eccentricity and omega is the argument of periapsis) for HAT-P-3b (<0.0081) and HAT-P-4b (<0.0042), based on the secondary eclipse timings.

Read more (699kb, PDF)