First Detection of Both Absorption and Emission of Molecular Hydrogen in Classical T Tauri Stars

Details First Detection of Both Absorption and Emission of Molecular Hydrogen in Classical T Tauri Stars First Detection of Both Absorption and Emission of Molecular Hydrogen in Classical T Tauri Stars

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733918l&link_type=abstract

American Astronomical Society, AAS Meeting #217, #339.18; Bulletin of the American Astronomical Society, Vol. 43, 2011

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Scientific paper

Classical T Tauri stars (CTTSs) show bright emission lines of molecular hydrogen in their ultraviolet spectra. These fluorescent emission lines are pumped by molecular hydrogen transitions coincident with the hydrogen Lyman-alpha emission line and other UV emission lines. While these emission lines have been studied in the UV spectra of many CTTSs, the pumping transitions have never been detected in absorption against the Lyman alpha emission line. Spectra obtained with the excellent sensitivity and low background of the new Cosmic Origin Spectrograph (COS) on HST now show absorption by the pumping transitions in two CTTSs, V4046 Sag and DF Tau. We compare the energy absorbed in each pumping transition to the energy emitted in the resulting fluorescent emission lines. The absorption/emission ratios are very different from unity, but the ratios at different wavelengths across the Lyman-alpha emission line of each star can be brought close to unity by assuming additional Lyman-alpha absorption along the line of sight. For V4046 Sag, a CTTS observed nearly face-on, the required absorption is near +290 km/s most likely due to hydrogen accreting onto the star. For DF Tau, a CTTS observed nearly edge-on, the line of sight absorption is near 0 km/s, indicating absorption in the disk. We shows models for both stars.
This work is supported by a NASA grant to the University of Colorado.

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