Abstract: We report on the first detection of the orbital velocity of an extrasolar planet, HD209458b. High dispersion ground-based spectroscopy during a transit of this planet reveals absorption lines from carbon monoxide produced in the planet atmosphere, which shift significantly in wavelength due to the change in the radial component of the planet orbital velocity. These observations result in an assumption-free mass determination of the star and planet using only Newton's law of gravity. A blueshift of the carbon monoxide signal with respect to the systemic velocity of the host star suggests the presence of a strong wind flowing from the irradiated dayside to the non-irradiated nightside of the planet within the 0.01-0.1 mbar atmospheric pressure range probed by these observations. The strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10^-3 in this planet’s upper atmosphere.

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ExoClimes 2010, Exeter, Wednesday 8^th Sep 2010