* Astronomy

Two new exoplanets and an unknown celestial object are the latest findings of the COROT mission. These discoveries mean that the mission has now found a total of four new exoplanets.
These results were presented this week at the IAU symposium 253 in Massachusetts, USA.

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Title: XO-4b: An Extrasolar Planet Transiting an F5V Star
Authors: P. R. McCullough, Christopher J. Burke, Jeff A. Valenti, Doug Long, Christopher M. Johns-Krull, P. Machalek, K. A. Janes, B. Taylor, J. Gregorio, C. N. Foote, Bruce L. Gary, M. Fleenor, Enrique García-Melendo, T. Vanmunster

We report the discovery of the planet XO-4b, which transits the star XO-4 (GSC 03793-01994, V=10.7, F5V). Transits are 1.0% deep and 4.4 hours in duration. The star XO-4 has a mass of 1.32 M_sun.... The planet XO-4b has a mass of 1.72 M_Jup....radius of 1.34 R_Jup...orbital period 4.125 days. We analyse scintillation-limited differential R-band photometry of XO-4b in transit made with a 1.8-m telescope under photometric conditions, yielding photometric precision of 0.6 to 2.0 millimag per one-minute interval. The declination of XO-4 places it within the continuous viewing zone of the Hubble Space Telescope (HST), which permits observation without interruption caused by occultation by the Earth. Because the stellar rotation periods of the three hottest stars orbited by transiting gas-giant planets are 2.0, 1.1, and 2.0 times the planetary orbital periods, we note the possibility of resonant interaction.

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Title: Theoretical Radii of Extrasolar Giant Planets: the Cases of TrES-4, XO-3b, and HAT-P-1b
Authors: Xin Liu, Adam Burrows, Laurent Ibgui

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 x solar metallicity with equilibrium molecular abundances. This heating rate is reasonable, and corresponds for an energy dissipation parameter (Q_p) of  ~10^5 to an eccentricity of  ~0.04, assuming 3 x solar atmospheric opacity. 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 re-examine 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 by burrows07b. 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  jackson08a,jackson08b, we suggest that this "clock-reset" effect could indeed be important in better explaining some observed transit radii.

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Title: Planetary Systems in Binaries. I. Dynamical Classification
Authors: Genya Takeda, Ryosuke Kita, Frederic A. Rasio (Northwestern Univ.)
(Version v2)

Many recent observational studies have concluded that planetary systems commonly exist in multiple-star systems. At least ~20% of the known extrasolar planetary systems are associated with one or more stellar companions. The orbits of stellar binaries hosting planetary systems are typically wider than 100 AU and often highly inclined with respect to the planetary orbits. The effect of secular perturbations from such an inclined binary orbit on a coupled system of planets, however, is little understood theoretically. In this paper we investigate various dynamical classes of double-planet systems in binaries through numerical integrations and we provide an analytic framework based on secular perturbation theories. Differential nodal precession of the planets is the key property that separates two distinct dynamical classes of multiple planets in binaries: (1) dynamically-rigid systems in which the orbital planes of planets precess in concert as if they were embedded in a rigid disk, and (2) weakly-coupled systems in which the mutual inclination angle between initially coplanar planets grows to large values on secular timescales. In the latter case, the quadrupole perturbation from the outer planet induces additional Kozai cycles and causes the orbital eccentricity of the inner planet to oscillate with large amplitudes. The cyclic angular momentum transfer from a stellar companion propagating inward through planets can significantly alter the orbital properties of the inner planet on shorter timescales. This perturbation propagation mechanism may offer important constraints on the presence of additional planets in known single-planet systems in binaries.

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