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Astron. Astrophys. 335, 510-516 (1998)

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Hot UV bright stars in globular clusters *

S. Moehler 1, 2, W. Landsman 3 and R. Napiwotzki 1

1 Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstrasse 7, D-96049 Bamberg, Germany
2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
3 Raytheon STX, NASA/GSFC, Greenbelt, MD 20770, USA

Received 19 February 1998 / Accepted 1 April 1998

Abstract

We have obtained medium-resolution spectra of seven UV-bright stars discovered on images of four southern globular clusters obtained with the Ultraviolet Imaging Telescope (UIT). Effective temperatures, surface gravities and helium abundances are derived from LTE and non-LTE model atmosphere fits. Three of the stars have sdO spectra, including M4-Y453 ([FORMULA] = 58800 K, [FORMULA] = 5.15), NGC 6723-III60 ([FORMULA] = 40600 K, [FORMULA] = 4.46) and NGC 6752-B2004 ([FORMULA] = 37000 K, [FORMULA] = 5.25). All seven stars lie along either post-extended horizontal branch (EHB) or post-early AGB evolutionary tracks. The post-early AGB stars show solar helium abundances, while the post-EHB stars are helium deficient, similar to their EHB progenitors.

Key words: stars: Post-AGB – globular clusters: individual: NGC 2808; NGC 6121; NGC 6723; NGC 6752 – ultraviolet: stars

* Based on observations collected at the European Southern Observatory (ESO N[FORMULA] 57.E-0101)

Send offprint requests to: S. Moehler

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© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998
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