A search for starlight reflected from upsilon And's innermost planet

Abstract

In data from three clear nights of a WHT/UES run in 2000 Oct/Nov, and using improved Doppler tomographic signal-analysis techniques, we have carried out a deep search for starlight reflected from the innermost of upsilon And's three planets. We place upper limits on the planet's radius R_p as functions of its projected orbital velocity K_p ~ 139 sin i km/sec for various assumptions about the wavelength-dependent geometric albedo spectrum p(λ) of its atmosphere. For a grey albedo p we find R_p \sqrt{p} < 0.98 R_Jup with 0.1 percent false-alarm probability (4-sigma). For a Sudarsky et al (2000) Class V model atmosphere, the mean albedo in our 380-676 nm bandpass is ~ 0.42, requiring R_p < 1.51 R_Jup, while an (isolated) Class IV model with ~ 0.19 requires R_p < 2.23 R_Jup. The star's v sin{i} ~ 10 km/sec and estimated rotation period P_{rot} ~ 10 d suggest a high orbital inclination i ~ 70-80 degrees. We also develop methods for assessing the false-alarm probabilities of faint candidate detections, and for extracting information about the albedo spectrum and other planetary parameters from faint reflected-light signals.