Predicting Photometric and Spectroscopic Signatures of Rings Around Transiting Extrasolar Planets

We present theoretical predictions for the photometric and spectroscopic signatures of rings around transiting extrasolar planets. On the basis of a general formulation for the transiting signature in the stellar light curve and the velocity anomaly due to the Rossiter effect, we compute the expected signals analytically for a face-on ring system, and numerically for more general configurations. We study the detectability of a ring around a transiting planet located at a = 3 AU for a variety of obliquity and azimuthal angles, and find that it is possible to detect the ring signature both photometrically and spectroscopically unless the ring is almost edge-on (i.e., the obliquity angle, θ, of the ring is much less than unity). We also consider the detectability of planetary rings around a close-in planet, HD 209458b (θ ≈ 90° − i orbit ≈ 3 32), and Saturn (θ ≈ 26 7) as illustrative examples. While the former is difficult to detect with the current precision (photometric precision of 10 −4 and radial velocity precision of 1 m s −1 ), a marginal detection of the latter is possible photometrically. If the future precision of the radial velocity measurement goes below 0.1 m s −1 , they will even be detectable from ground-based spectroscopic observations.