Physics
Scientific paper
Jun 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........6p&link_type=abstract
Ph.D. Thesis California Inst. of Tech., Pasadena.
Physics
1
Metallicity, Molecular Clouds, Photosphere, Pre-Main Sequence Stars, Stellar Spectra, T Tauri Stars, Aluminum, Calcium, Iron, Nickel, Spectrographs, Titanium, Turbulence, Vanadium
Scientific paper
This thesis investigation uses photospheric abundance analysis techniques to determine metal abundances both for individual weakly active T Tauri stars and the molecular clouds with which these stars are associated. Using the high resolution echelle spectrographs of the Palomar 1.5m and the Las Campanas Observatory 2.5m telescopes, high signal-to-noise ratio spectra have been obtained for 53 low pre-main sequence stars in six major northern and southern hemisphere star formation regions. Spectra were also taken of 14 main sequence stars with known effective temperatures and metallicity to serve as spectral standards. Equivalent widths of a large number of Fe I absorption lines have been measured, as well as lines of Ca I, Al I, V I, Ni I, Ti I, K I, and Li I. Temperature-sensitive line ratios of neutral iron and vanadium calibrated against the spectral standards are used to derive effective temperatures for 30 weak-line T Tauri stars, which are much improved over the low resolution spectral classifications found for these objects in the literature. Microturbulent velocities have also been found for 16 of the pre-main sequence stars in the sample. Several stars with abnormally high microturbulences for their spectral type have been found. Using these improved stellar parameters, metallicities of a large number of T Tauri stars have been determined for the first time. Abundance analyses of iron, aluminum, calcium, nickel, and titanium are performed on 30 low masses, pre-main sequence stars. In the star-formation regions of Taurus-Auriga, Orion, Chamaeleon, and Ophiuchus, which each contributed five or more association members to the young star survey, bulk metallicities have been determined. The results indicate that the current metal abundances in these clouds are near or slightly above solar values. Cloud material metallicities are then used to calibrate ultraviolet line-of-sight metal depletion studies for the Orion and rho Ophiuchi clouds. The final chapter of this work is a lithium abundance analysis for the entire sample of 53 pre-main sequence stars.
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