Photometric Light Curves and Polarization of Close-in Extrasolar Giant Planets

The close-in extrasolar giant planets (CEGPs), <~0.05 AU from their parent stars, may have a large component of optically reflected light. We present theoretical optical photometric light curves and polarization curves for the CEGP systems from reflected planetary light. Different particle sizes of three condensates are considered. In the most reflective case, the variability is ~100 μmag, which will be easily detectable by the upcoming satellite missions Microvariability and Oscillations of Stars (MOST), COROT, and Measuring Oscillations in Nearby Stars (MONS), and possibly from the ground in the near future. The least reflective case is caused by small, highly absorbing grains such as solid Fe, with variation of much less than 1 μmag. Polarization for all cases is lower than current detectability limits. We also discuss the temperature-pressure profiles and resulting emergent spectra of the CEGP atmospheres. We discuss the observational results of τ Boo b by Cameron et al. and Charbonneau et al. in context of our model results. The predictions-the shape and magnitude of the light curves and polarization curves-are highly dependent on the sizes and types of condensates present in the planetary atmosphere.