Article

# Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b

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(Impact Factor: 6.28). 12/2008; 686(1):649. DOI: 10.1086/591078
Source: arXiv

ABSTRACT We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, λ = 3.7°± 2.1°. The small value of λ for this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial velocity measurements with those obtained previously.

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##### Article: Theoretical Radii of Extrasolar Giant Planets: the Cases of TrES-4, XO-3b, and HAT-P-1b
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ABSTRACT: To explain their observed radii, we present theoretical radius-age trajectories for the extrasolar giant planets (EGPs) TrES-4, XO-3b, and HAT-P-1b. We factor in variations in atmospheric opacity, the presence of an inner heavy-element core, and possible heating due to orbital tidal dissipation. A small, yet non-zero, degree of core heating is needed to explain the observed radius of TrES-4, unless its atmospheric opacity is significantly larger than a value equivalent to that at 10$\times$solar metallicity with equilibrium molecular abundances. This heating rate is reasonable, and corresponds for an energy dissipation parameter ($Q_p$) of $\sim10^{3.8}$ to an eccentricity of $\sim$0.01, assuming 3$\times$solar atmospheric opacity and a heavy-element core of $M_c = 30$ $M_{\oplus}$. For XO-3b, which has an observed orbital eccentricity of 0.26, we show that tidal heating needs to be taken into account to explain its observed radius. Furthermore, we reexamine the core mass needed for HAT-P-1b in light of new measurements and find that it now generally follows the correlation between stellar metallicity and core mass suggested recently. Given various core heating rates, theoretical grids and fitting formulae for a giant planet's equilibrium radius and equilibration timescale are provided for planet masses $M_p=$ 0.5, 1.0, and 1.5 $M_J$ with $a =$ 0.02-0.06 AU, orbiting a G2V star. When the equilibration timescale is much shorter than that of tidal heating variation, the effective age'' of the planet is shortened, resulting in evolutionary trajectories more like those of younger EGPs. Motivated by the work of \citet{jackson08a,jackson08b}, we suggest that this effect could indeed be important in better explaining some observed transit radii. Comment: 11 pages; references added; ApJ accepted version
The Astrophysical Journal 05/2008; 687(2). DOI:10.1086/592189 · 6.28 Impact Factor
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##### Article: A time-dependent radiative model for the atmosphere of the eccentric exoplanets
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ABSTRACT: We present a time-dependent radiative model for the atmosphere of extrasolar planets that takes into account the eccentricity of their orbit. In addition to the modulation of stellar irradiation by the varying planet-star distance, the pseudo-synchronous rotation of the planets may play a significant role. We include both of these time-dependent effects when modeling the planetary thermal structure. We investigate the thermal structure and spectral characteristics for time-dependent stellar heating for two highly eccentric planets. Finally, we discuss observational aspects for those planets suitable for Spitzer measurements and investigate the role of the rotation rate.
The Astrophysical Journal 07/2008; 712(1). DOI:10.1017/S1743921308027099 · 6.28 Impact Factor