AAS 201st Meeting, January, 2003
Session 25. Circumstellar Material and Mass Loss
Oral, Monday, January 6, 2003, 10:00-11:30am, 602-604

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[25.02D] Ultraviolet Spectroscopy of Circumstellar Disks

A. Roberge, P. D. Feldman (JHU), A. Lecavelier des Etangs, A. Vidal-Madjar (IAP), M. Deleuil, J.-C. Bouret (LAS de Marseille, CNRS)

We present a study of gas in several young circumstellar (CS) disk systems, using UV absorption spectroscopy with HST-STIS and FUSE. The systems observed are Beta~Pictoris, AB~Aurigae, 51~Ophiuchi, HD~100546, and HD~163296. This study focusses on molecular gas abundances and star-grazing planetesimals, and shows that the characteristics of the CS gas can aid in the evolutionary classification of disk systems. CS molecular gas abundances, which have been the subject of considerable recent controversy, may also provide information on the composition of extrasolar planetesimals.

Important results on the individual systems are listed below. The primordial disk system AB~Aurigae is surrounded by a diffuse envelope of gas and dust, a remnant of the molecular cloud that collapsed to form the star. Carbon monoxide and CI are observed in the Beta~Pic debris disk; when compared to the lack of molecular hydrogen gas, this indicates that the CO gas is produced by evaporation of icy, comet-like planetesimals. Volatile-depleted or metal-rich CS gas is seen infalling toward the star in spectra of 51~Oph; this gas is likely produced by vaporization of star-grazing planetesimals. Analysis of the transitional disk systems HD~100546 and~HD 163296 shows extraordinary hot, dense molecular hydrogen near these stars.

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