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D. Deming (GSFC), L. J. Richardson (LASP & GSFC), C. Goukenleuque (GSFC), J. Harrington (Cornell Univ.), G. Wiedemann (Univ. Jena)
We have conducted ground-based infrared spectroscopic observations during two secondary eclipses of the only known transiting extrasolar planet, HD209458b. We are using the technique of "occultation spectroscopy" (Richardson et al. 2003, Ap.J., in press) to separate the 2 to 4 micron spectrum of the planet from the combined light of the system. Frequent observations of a close comparison star (HD210483) allow us to remove the effects of the terrestrial atmosphere and minimize other errors in excess of the photon noise. Due to excellent observing conditions, we were able to acquire approximately 2500 spectra, equally divided between HD209458 and HD210483, using the SpeX spectrometer at the NASA IRTF on Mauna Kea in September 2001. We exploit the secondary eclipse - when the planet passes behind the star - to isolate the spectrum of the planet. Models of the exoplanet spectrum predict a maximum planet-to-star contrast in the L band near 3.9 microns, with peak contrast values in the approximate range from 3000 to 800 parts-per-million (ppm). Our 1-sigma error level is currently about 500 ppm - already sufficient to rule out the most optimistic contrast values. We are working to decorrelate the remaining noise sources from our data, and refine our analysis toward a measurement of the infrared spectrum of HD209458b.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.