The New Transiting Planet OGLE‐TR‐56b: Orbit and Atmosphere

Abstract

Motivated by the identification of the very close-in extrasolar giant planet OGLE-TR-56b (P = 1.2 days, a = 0.023 AU, Mp = 0.9MJ), we explore implications of its existence for problems of tidal dissipation, planet migration, and atmospheric stability. The small orbit of OGLE-TR-56b makes the planet an interesting test particle case for tidal dissipation in stellar convection zones. We show that it favors prescriptions of suppressed convective eddy viscosity. Precise timing of the transits of OGLE-TR-56b might place interesting constraints on stellar convection theory if orbital period change is detected in the near future. Another interesting issue related to the new planet is the origin of its close orbit; OGLE-TR-56b may be a survivor of Roche lobe overflow mass loss. Living in such close proximity to its parent star, OGLE-TR-56b should have temperatures in the dayside hemisphere reaching 1900 K, and we find that only few condensates could form clouds, if at all, under those conditions—mostly Al2O3 and Fe(s). We explore the issue of atmosphere evaporation and find that the planet's atmosphere is stable over its lifetime. The large size of the planet (Rp = 1.3 ± 0.15 RJ) might also require additional energy, similar to HD 209458b.