AAS 195th Meeting, January 2000
Session 24. Extrasolar Planets and Substellar Companions
Oral, Wednesday, January 12, 2000, 10:00-11:30am, Regency VI

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[24.03] Extrasolar Giant Planets Under Strong Stellar Irradiation

S. Seager (Institute for Advanced Study)

The discovery of 51 Peg b in 1995, only 0.05 AU from its parent star, heralded an unexpected new class of planets. Since that time, several more Jupiter-mass ``close-in'' extrasolar giant planets (CEGPs) have been discovered. Five times closer to their parent stars than Mercury is to our Sun, the CEGPs are highly irradiated by their parent stars. Their atmospheric structures and emergent spectra are strongly affected by the intense irradiation; at effective temperatures of 1100 to 1600~K their atmospheres are more similar to those of brown dwarfs and L dwarfs than to those of our own Solar System planets. Because of the proximity to the parent star, reflected optical stellar flux may make the CEGPs the first directly detected extrasolar planets.

I will present theoretical spectra, photometric light curves, polarization curves, and atmosphere temperature-pressure structures of the CEGPs. All of these are highly dependent on the type and size of condensates assumed to be present in the planet atmosphere. Using a three-condensate mix of MgSiO3, Fe, and Al2O3, and exploring a range of mean particle sizes, the light curves at 5500~Å~range in amplitude from 65~\mumag down to 0.25~\mumag, and for large particle size compared to wavelength can appear very different from a sine curve. The polarization of the CEGPs is not detectable with current technology, even in the best case. The spectra also vary strongly depending on the type and size of condensate assumed, and in the most reflective case the optical flux can be a few orders of magnitude greater than that of an isolated planet of the same effective temperature. However, in general the main features are: exact reflected stellar features in the blue and UV; reflected stellar light in the optical with neutral alkali metal absorption lines from the planet atmosphere; and H2O absorption bands in the infrared from thermal emission. CH4 is an excellent diagnostic, since the absorption features appear only in models where the condensates are not strongly absorbing, i.e. where the atmosphere is not strongly heated by the stellar radiation.

The author(s) of this abstract have provided an email address for comments about the abstract: seager@sns.ias.edu

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