Predicting Photometric and Spectroscopic Signatures of Rings around Transiting Extrasolar Planets

We present theoretical predictions for 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 = 3AU 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 of the ring θ is much less than unity). We also consider the detectability of planetary rings around a close-in planet, HD 209458b (θ ≈ 90 − iorbit ≈ 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 and radial velocity precision of 1 m s), a marginal detection of the latter is possible photometrically. If the future precision of the radial velocity measurement reaches even below 0.1 m s, they will be even detectable from the ground-based spectroscopic observations. Subject headings: planets:, techniques:spectroscopic also at Research Center for the Early Universe (RESCEU), School of Science, The University of Tokyo, Tokyo 113-0033, Japan. 2 also at Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8568, Japan