A Reconnaissance of the 900-1200 A Spectra of Early O Stars in the Magellanic Clouds

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Session 30 -- First Results from Astro 2
Oral presentation, Tuesday, June 13, 1995, 2:00pm - 5:30pm

[30.08] A Reconnaissance of the 900-1200 A Spectra of Early O Stars in the Magellanic Clouds

N.R. Walborn, K.S. Long (STScI), R.-P. Kudritzki, D.J. Lennon (Munich Univ.)

The Hopkins Ultraviolet Telescope on the Astro-2 mission has enabled the first survey of O-type spectra below 1200 A in the Magellanic Clouds. Nine O stars and one WN were observed, half in each of the Large and Small Clouds. Among them are four O3 giants, including an LMC object which is the current candidate for the most massive star known, and one in the SMC with an evident large N/C ratio in its wind. The systematics of the O VI wind features in such spectra can now be studied for the first time. Two O4 If stars in the LMC, which have very similar parameters except for the rotational velocities, are found to have quite different relative strengths of their CNO features. An O7 If supergiant and the unstable WN binary HD 5980 in the SMC were also observed. The future of this subject lies in the Magellanic Clouds, because just a few tenths of a magnitude of reddening is sufficient for the associated extinction and molecular hydrogen absorption to obliterate the far-UV spectra of the OB stars. All of the O stars in the present sample are included in the Munich HST/ESO programs at longer wavelengths, so that the new far-UV information can be immediately incorporated into their model analyses. The results will be relevant to the study of massive stellar winds and evolution at different metallicities, as well as to the synthesis of starburst spectra.

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