Search for an Atmospheric Signature of the Transiting Exoplanet HD 149026

HD149026b is a short-period, Saturn-mass planet that transits a metalrich star. The planet radius, determined by photometry, is remarkably small compared to other known transiting planets, with a heavy element core that apparently comprises ∼ 70% of the total planet mass. Time series spectra were obtained at Keck before and during transit in order to model the RossiterMcLaughlin effect. Here, we make use of these observations to carry out a differential comparison of spectra obtained in and out-of-transit to search for signatures of neutral atomic lithium and potassium from the planet atmosphere. No signal was detected at the 2% level; we therefore place upper limits on the column density of these atoms. Subject headings: planetary systems — stars: individual (HD 149026) — transit effects Based on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Keck time has been granted by NASA. Department of Physics & Astronomy, San Francisco State University, San Francisco, CA 94132; [email protected] Space Science and Astrobiology Division, NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035; [email protected] Spitzer Fellow SETI Institute, 515 North Whisman Road, Mountain View, CA 94043 Department of Astronomy, University of California, Berkeley, CA USA 94720