Computer Science
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt........18s&link_type=abstract
Thesis (PhD). CORNELL UNIVERSITY, Source DAI-B 62/03, p. 1433, Sep 2001, 205 pages.
Computer Science
1
Scientific paper
We present 8-13 μm spectra at resolution R ~ 600 of 29 northern Galactic Wolf-Rayet stars, covering a broad range of spectral subtypes, including 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN star. Most constitute the first ever reported mid-infrared spectrum. Lines of He I and He II, accompanied in some stars by [Ne II] and [S IV], are strongly present in 22 of the sources observed, while 6 of the sources exhibit the powerful emission of heated circumstellar carbon dust. Correspondence with optically determined subtypes is found to be incomplete, with significant deviations for later types seen in both WN and WC. For a single WC star, WR 121, neon abundance is estimated from [Ne II] emission, and found to be ~7× the cosmic value, as predicted by long-standing but contested evolved core nucleosynthesis calculations. The observed line parameters are used in a population synthesis model to quantify the contribution of WR stars to the total integrated emission of a single 106 Msolar stellar population formed in an instantaneous burst, and including a T <= 70 K dust emission component with L ir/Lblue = 0.1. After ~5 Myr, the infrared emission lines which form in the WR winds achieve similar line luminosities and equivalent widths in the aggregate starburst spectrum as the commonly used optical λ4686 ``WR Bump'', when the stars are embedded in dust providing AV >= 5 magnitudes of screen extinction. We address the possibility of direct detection of these infrared wind lines, which may be possible in star- forming galaxies if a significant population of recently formed stars is hidden by dust, and the starburst is observed against a relatively low-level stellar background. A mid-infrared spectrum of Wolf-Rayet Galaxy NGC 5253 is presented, but hot dust overwhelms these line features. We estimate that 5 × 105 WR stars would be required for direct detection of mid- infrared wind lines in this nearby dwarf galaxy, with substantially fewer required for strong near-infrared lines. Observations were made with SCORE, a unique mid-infrared spectrograph built as a prototype of SIRTF's short-wavelength high-resolution spectrograph module. SCORE achieves spectral sensitivity similar to the Infrared Space Observatory. Important details of the instrument are presented, along with new techniques developed for the extraction of SCORE spectral data.
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