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Astronomy Colloquium
"Recent results from the Cosmic Origins Spectrograph HD 209458b...."
Date: Thursday, October 28th
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Jeffrey Linsky, JILA, University of Colorado
Abstract: 209458b was the first transiting planet to be studied in detail. <br>
It is a Jupiter mass exoplanet with a 3.5 day orbit around a solarlike star. We have used the new Cosmic Origins Spectrograph on Hubble to obtain very sensitive ultraviolet spectra during transit and three nontransit phases in order to measure the mass loss properties of the exoplanet. During transit, absorption by singly-ionized carbon and doubly-ionized silicon in the planet's exosphere reduces the observed stellar emission by 8% compared to the 1.5% reduction predicted by the planet's size. Velocity resolution of these line profiles leads to estimates of the mass loss rate and the identification of enhanced massloss directed away from the star. The planet has a cometlike tail!

I will also describe our preliminary analysis of molecular hydrogen pumping and fluorescence in the disks of premain sequence stars. The origin of the bright fluorescent emission seen in the ultraviolet spectra of these stars has been ascribed to pumping by the stellar Lyman-alpha emission line, but until now there has been no direct evidence for this pumping. The very sensitive COS instrument now allows us to observe absorption against the Lyman-alpha emission line at the pumping transitions. Energy balance between absorption and emission allows us to estimate the accretion rates for DF Tau and V4046 Sag.

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