Astron. Astrophys. 361, 937-944 (2000)

Blue horizontal branch stars in metal-rich globular clusters

II. 47 Tucanae and NGC 362

S. Moehler ^{*  1}, W.B. Landsman ² and B. Dorman <sup>2

1</sup> Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany (ai13@sternwarte.uni-erlangen.de)
² Raytheon ITSS, NASA/GSFC, Greenbelt, MD 20770, USA (landsman@mpb.gsfc.nasa.gov; dorman@veris.gsfc.nasa.gov)

Received 3 July 2000 / Accepted 11 August 2000

Abstract

Atmospheric parameters (, ), and radial velocities are derived for twelve candidate blue horizontal branch (HB) stars in the globular clusters 47 Tuc and NGC 362, which so far have been known to contain primarily red HB stars. The spectroscopic targets were selected from the catalog of hot stars detected in these clusters at 1600 Å using the Ultraviolet Imaging Telescope (UIT). Spectroscopic analyses of these stars reveal, however, that one of the four HB candidates targets in 47 Tuc, and five out of the eight targets in NGC 362 are probably background stars belonging to the Small Magellanic Cloud. With the exception of the photometric binary MJ38529 in 47 Tuc, the parameters of those stars that are probable members of 47 Tuc and NGC 362 agree well with canonical HB evolution. The three hot stars in 47 Tuc all have 10,000 K 15,000 K and include one photometric binary, which suggests that they might have a different physical origin than the dominant red HB population. The somewhat cooler blue HB stars in NGC 362 show more continuity with the dominant red HB population and might simply arise from red giants with unusually high mass loss.

Key words: stars: early-type stars: horizontal-branch stars: Population II Galaxy: globular clusters: individual: NGC 104, NGC 362

* Based on observations collected at the European Southern Observatory (ESO N^o 60.E-0145)

Send offprint requests to: S. Moehler

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Contents

• 1. Introduction
• 2. Observations
• 3. Data reduction
• 4. Atmospheric parameters
  • 4.1. derived from energy distributions
  • 4.2. Balmer line profile fits
  • 4.3. Comparison of effective temperatures obtained with different methods
  • 4.4. Masses
• 5. Discussion
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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