Computer Science
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt........12r&link_type=abstract
Thesis (PhD). THE JOHNS HOPKINS UNIVERSITY, Source DAI-B 63/10, p. 4723, Apr 2003, 155 pages.
Computer Science
2
Scientific paper
The gas in circumstellar (CS) disks, about which little is known, has been the focus of recent intensive study with multiband spectroscopy. CS disks divide into two primary classes, (1)primordial disks, which are composed of unprocessed interstellar molecular cloud material, and (2)debris disks, which are composed of gas and dust produced by the destruction of solid planetary bodies. To these two classes, a third may be added, transitional disks, which are in the process of evolving from primordial to debris disks. The timescale over which the primordial CS gas disappears and the exact conditions of the transformation are of critical importance to our understanding of planetary formation. This dissertation presents a study of CS gas in several disk systems, using UV spectroscopy with HST-STIS and FUSE. The systems observed are β Pictoris, AB Aurigae, 51 Ophiuchi, HD 100546, and HD 163296. This study focusses on, but is not limited to, molecular gas abundances and star-grazing planetesimals. This work 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 Aur is surrounded by a diffuse envelope of gas and dust, a remnant of the molecular cloud that collapsed to form the star. CO and C I are observed in the β Pic debris disk; when compared to the lack of H2 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. Preliminary analysis of the transitional disk systems HD 100546 and HD 163296 show several indications of a young evolutionary state.
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