Irradiated Planets

Abstract

We have modeled irradiated planets located near a dM5 and a G2 primary star. The impinging radiation field was explicitly included in the solution of the radiative transfer equation and in the computation of the atmospheric structure. We find that large errors in both the thermal and reflected flux will result from models that do not include the impinging radiation in a self-consistent manner. A cool (T_eff = 500 K) and a hot (T_eff = 1000 K) planet were modeled at various orbital separations from both the dM5 star and the G2 primary. In all scenarios, we compared the effects of the irradiation in two extreme cases: one where dust clouds form and remain suspended in the atmosphere and another where dust clouds form but completely settle out of the atmosphere. The atmospheric structure and emergent spectrum strongly depend on the presence or absence of dust clouds. We find that in the absence of dust opacity, the impinging radiation significantly alters the innermost layers of an extrasolar giant planet atmosphere and that they are actually brighter in the optical than dusty planets. Our models also indicate that the planet-to-star brightness ratio in the optical will be less that 1 × 10^-5 for objects like τ Bootis, which is consistent with recently reported upper limit values.