A New Search for Carbon Monoxide Absorption in the Transmission Spectrum of the Extrasolar Planet HD 209458b1

We have revisited the search for carbon monoxide absorption features in transmission during the transit of the extrasolar planet HD209458b. In AugustSeptember 2002 we acquired a total of 1077 high resolution spectra (λ/δλ ∼ 25, 000) in the K-band (2 μm) wavelength region using NIRSPEC on the Keck II telescope during three transits. These data are more numerous and of better quality than the data analyzed in an initial search by Brown et al. Our analysis achieves a sensitivity sufficient to test the degree of CO absorption in the first overtone bands during transit, based on plausible models of the planetary atmosphere. We analyze our observations by comparison to theoretical tangent Data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. NASA’s Goddard Space Flight Center, Planetary Systems Branch, Code 693, Greenbelt MD 20771, email: [email protected] High Altitude Observatory/National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder CO 80307, email: [email protected] The National Center for Atmospheric Research is sponsored by the National Science Foundation. California Institute of Technology, 105-24 (Astronomy), 1200 E. California Blvd., Pasadena, CA 91125, Present address: Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-16, Cambridge, MA 02138, email: [email protected] Center for Radiophysics and Space Research, Cornell University, 326 Space Sciences Bldg., Ithaca, NY 14853-6801, email: [email protected] National Research Council, NASA’s Goddard Space Flight Center, Infrared Astrophysics Branch, Code 685, Greenbelt MD 20771, email: [email protected]