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D. Deming (NASA GSFC), G. Wiedemann (ESO), G. Bjoraker (NASA GSFC)
We have searched for a methane signature in the infrared spectrum of Tau Bootis, produced by the planetary companion. The observations comprise 598 low-noise (S/N ~ 100), high resolution (4 x 104) spectra near 3044 cm-1, which we analyze by cross-correlating with a modeled planetary spectrum based on the work of Burrows and Sharp (1999), and Sudarsky et al. (2000). The 3-sigma random noise level of our analysis is ~6 x 10-5 stellar continuum flux units, and the confusion noise limit is ~ 2.5 x 10-4.
We find a significant cross-correlation amplitude of ~ 3.3 x 10-4 continuum units at a velocity near that of the star. A weaker, and much more diffuse, feature of intensity amplitude ~2 x 10-4 continuum units occurs at a velocity amplitude of 71 (±10) km sec-1, in agreement with the orbit claimed for the planet by Cameron et al. (1999). Both features have passed several tests designed to reject systematic errors. We interpret the first feature as evidence for circumstellar methane absorption, and we discuss the possibility that the second feature is due to the planet.
This work was supported by the NASA Origins of Solar Systems program.