An Upper Limit on the Reflected Light from the Planet Orbiting the Star τ Bootis

The planet orbiting τ Boo at a separation of 0.046 AU could produce a reflected light flux as bright as 1 × 10-4 relative to that of the star. A spectrum of the system will contain a reflected light component which varies in amplitude and Doppler shift as the planet orbits the star. Assuming the secondary spectrum is primarily the reflected stellar spectrum, we can limit the relative reflected light flux to be less than 5 × 10-5. This implies an upper limit of 0.3 for the planetary geometric albedo near 480 nm, assuming a planetary radius of 1.2 RJup. This albedo is significantly less than that of any of the giant planets of the solar system and is not consistent with certain published theoretical predictions.