On using the Rossiter Effect to Detect Terrestrial Planets

Abstract. We explore the possibility that the transit signature of an Earthsize planet can be detected in spectroscopic velocity shifts via the Rossiter effect. Under optimistic but not unrealistic conditions, it should be possible to detect a large terrestrial-size planet. While not suitable for discovering planets, this method can be used to confirm suspected planets. The Rossiter effect is seen as a radial velocity “anomaly ” during transit (see Gaudi & Winn 2007, and the contribution by Winn in these proceedings). The distortion in the radial velocity curve can be large because the effect scales with the rotational velocity of the star which is very much larger than its orbital velocity, e.g. km/s vs. m/s. So even though a small fractional area of the star is occulted, the loss of light breaks the exquisite symmetry of the photosphere and a distortion of the line profile occurs. The skewed line profile then gives rise to an apparent radial velocity shift. It is important to realize that there is no real change in stellar velocity — there is only a change in line shape that mimics a change in velocity when the line is used to measure the Doppler reflex