Physics – Optics
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........3o&link_type=abstract
Thesis (PhD). UNIVERSITY OF VIRGINIA, Source DAI-B 61/06, p. 3094, Dec 2000, 243 pages.
Physics
Optics
Scientific paper
This work covers the far-ultraviolet (FUV; 900-1200 Å) imaging performance of telescope mirrors for the Far Ultraviolet Spectroscopic Explorer (FUSE) and presents Ultraviolet Imaging Telescope (UIT) observations of early-type galaxies (1550 Å) and FUSE spectra of a subdwarf B star and two O7 supergiants. FUSE Mirror Imaging Performance. The imaging performance of optics at short wavelengths (UV-X-ray) is dependent on figure quality and small-scale surface roughness. We developed a novel interferometric alignment technique for off-axis parabolic mirrors used for laboratory testing. During mirror assembly, we investigated and mitigated mount- related distortions which contributed to figure error. We performed extensive metrology, image testing and analysis to predict the on-orbit, FUV point spread function. The FUSE mirrors meet mission imaging requirements. UIT Observations of Early-Type Galaxies. Early UV space astronomy missions revealed that early-type galaxies harbor a population of stars with effective temperatures greater than that of the main sequence turn-off (~6,000 K) and UV emission that is very sensitive to characteristics of the stellar population. We present UV (1550 Å) surface photometry and UV-B color profiles for 8 E and S0 galaxies observed by UIT. Some objects have de Vaucouleurs surface brightness profiles, while others have disk-like profiles, but we find no other evidence for the presence of a disk or young, massive stars. There is a wide range of UV-B color gradients, but there is no correlation with metallicity gradients. Analysis of the FUSE Spectrum of a Subdwarf B Star. Subdwarf B (sdB) stars are the leading candidate UV emitters in old, high metallicity stellar populations (e.g., early-type galaxies). We observed the Galactic sdB star PG0749+658 with FUSE and derived abundances with the aim of constraining models of the heavy element distribution in sdB atmospheres. All of the elements measured are depleted with respect to solar, except for Cr and Mn, which are about solar, and Ni, which is enhanced. FUSE Observations of O Star Winds. The resonance transitions of ions in the rarefied, supersonic winds of massive stars form distinctive UV absorption and emission lines called P Cygni profiles, which can reveal the velocity and density structure of the wind. We discuss some of the P Cygni profiles in the FUSE spectra of two O7 supergiants, one in the Small and one in the Large Magellanic Cloud. We measure the terminal velocity of the wind of each star and the total column density of C and N ions. This analysis sheds light on the main sequence mass loss of two stars with similar spectral type in different populations.
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