Astron. Astrophys. 337, 39-42 (1998)

Young massive stellar populations in M 33

G.R. Ivanov

Department of Astronomy, Sofia University, 5 James Bourchier Avn., BG-1164 Sofia, Bulgaria

Received 7 October 1997 / Accepted 27 March 1998

Abstract

In this paper we estimate the ratio OB stars to red supergiants (OB/R) as a function of the distance from the centre of M 33. We found a gradient of the ratio (OB/R) really exists. Our study is based on a new approach in estimating the errors on the ratio (OB/R). On the other hand, by applying a new correlation technique between OB star candidates and red supergiant candidates in the central region of M 33, the gradient becomes pronounced. Our results confirm the existence of such a gradient and we consider this fact as a consequence of a similar gradient of the chemical abundance in M 33.

Key words: methods: data analysis stars: supergiants galaxies: M 33 galaxies: stellar content

Send offprint requests to: G.R. Ivanov

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Contents

• 1. Introduction
• 2. Correlation technique
• 3. Correlation between stellar populations in M 33
  • 3.1. Correlation between OB stars and other stellar populations
  • 3.2. Photographic UBV-photometry
• 4. Discussion
  • 4.1. Limited probabilities for selection of associated and foreground couples
  • 4.2. The ratio OB stars to RSGs (OB/R)
  • 4.3. Observational evidences of the evolution of massive stars
• 5. Summary
• Acknowledgements
• Appendix A: derivation of Eq. (1)
• References

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998
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