Tau Boo b: Hunting for reflected starlight

TL;DR

This study searches for reflected starlight from Tau Boo b to determine its atmospheric albedo and orbital inclination, but only sets upper limits due to non-detection, confirming the planet's low reflectivity.

Contribution

First high-resolution spectral analysis attempting to detect reflected light from Tau Boo b, providing constraints on its atmospheric properties and orbital inclination.

Findings

No definitive detection of reflected light was made.

Upper limits on planet-to-star flux ratio were established.

The geometric albedo is constrained to be less than 0.40.

Abstract

Aims. We attempt to detect starlight reflected from the hot Jupiter orbiting the main-sequence star Tau Boo, in order to determine the albedo of the planetary atmosphere, the orbital inclination of the planetary system and the exact mass of the planetary companion. Methods. We analyze high-precision, high-resolution spectra, collected over two half nights using UVES at the VLT/UT2, by way of data synthesis. We interpret our data using two different atmospheric models for hot Jupiters. Results. Although a weak candidate signal appears near the most probable radial velocity amplitude, its statistical significance is insufficient for us to claim a detection. However, this feature agrees very well with a completely independently obtained result by another research group, which searched for reflected light from Tau Boo b. As a consequence of the non-detection of reflected light, we place upper limits to the planet-to-star flux ratio at the 99.9% significance level. For the most probable orbital inclination around i = 46 degrees, we can limit the relative reflected radiation to be less than 5.7 x 10^-5 for grey albedo. This implies a geometric albedo smaller than 0.40, assuming a planetary radius of 1.2 R_Jup .