The Search for an Atmospheric Signature of the Transiting Exoplanet HD 149026b1

Abstract

HD 149026b is a short-period, Saturn-mass planet that transits ametal-rich star. The planet's radius, determined by photometry, isremarkably small compared to other known transiting planets, with aheavy-element core that apparently comprises ~70% of the total planetmass. Time-series spectra were obtained at Keck before and duringtransit in order to model the Rossiter-McLaughlin effect. Here we makeuse of these observations to carry out a differential comparison ofspectra obtained in and out of transit to search for signatures ofneutral atomic lithium and potassium from the planet atmosphere. Nosignal was detected at the 2% level; we therefore place upper limits onthe column density of these atoms.Based on observations obtained at the W. M. Keck Observatory, which isoperated by the University of California and the California Institute ofTechnology. Keck time has been granted by NASA.