Quantitative Studies of the Far-Ultraviolet, Ultraviolet, and Optical Spectra of Late O- and Early B-Type Supergiants in the Magellanic Clouds
Abstract
We present quantitative studies of eight late O- and early B-type supergiants in the Magellanic Clouds using far-ultraviolet Far Ultraviolet Spectroscopic Explorer, ultraviolet International Ultraviolet Explorer/Hubble Space Telescope, and optical VLT-UVES spectroscopy. Temperatures, mass-loss rates, and CNO abundances are obtained using the non-LTE, spherical, line-blanketed model atmosphere code of Hillier & Miller. We support recent results for lower temperatures of OB-type supergiants as a result of stellar winds and blanketing, which amounts to ~2000 K at B0 Ia. In general, Hα-derived mass-loss rates are consistent with UV and far-UV spectroscopy, although from consideration of the S IV λλ1063, 1073 doublet, clumped winds are preferred over homogenous models. AV 235 (B0 Iaw) is a notable exception, which has an unusually strong Hα profile that is inconsistent with the other Balmer lines and UV wind diagnostics. We also derive CNO abundances for our sample, revealing substantial nitrogen enrichment, with carbon and oxygen depletion. Our results are supported by comparison with the Galactic supergiant HD 2905 (BC0.7 Ia) for which near-solar CNO abundances are obtained. This bolsters previous suggestions that ``normal'' OB-type supergiants exhibit atmospheric compositions indicative of partial CNO processing.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated by Johns Hopkins University under NASA contract NAS5-32985. Also based in part on observations collected at the European Southern Observatory Very Large Telescope in program 67.D-0238, plus archival data obtained with the NASA-ESA Hubble Space Telescope and the NASA-ESA-PPARC International Ultraviolet Explorer.- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2004
- DOI:
- 10.1086/421769
- arXiv:
- arXiv:astro-ph/0404231
- Bibcode:
- 2004ApJ...610.1021E
- Keywords:
-
- Stars: Early-Type;
- Stars: Fundamental Parameters;
- Stars: Mass Loss;
- Ultraviolet: Stars;
- Astrophysics
- E-Print:
- 47 pages, 15 figures (reduced size). Accepted for publication in ApJ. A postscript version with full res. figs is available from http://www.ing.iac.es/~cje/lateO.ps.gz