Astron. Astrophys. 330, 492-504 (1998)

Evolutionary status and age spread in the young LMC cluster NGC 1850A ^*

V. Caloi and A. Cassatella

Istituto di Astrofisica Spaziale C.N.R., C.P. 67, I-00044 Frascati, Italy

Received 10 July 1997 / Accepted 1 October 1997

Abstract

IUE spectra have been obtained for 15 members of the very young LMC cluster NGC 1850A. The extinction law toward the cluster is similar to the one generally accepted for the 30 Dor region. We derive the effective temperatures and bolometric luminosities to estimate the age and mass for each star. An age spread of 2 to 10 Myr is estimated, suggesting a more or less continuous star formation process. The cluster contains at least four objects with mass 55 , still close to the main sequence. The age of the main cluster NGC 1850 is estimated to be about 50 Myr.

Key words: clusters: globular: NGC 1850A(LMC) Magellanic Clouds stars: evolution UV: stars galaxies: star clusters

* Based on observations collected by the International Ultraviolet Explorer (IUE) at the Villafranca Satellite Tracking Station of the European Space Agency.

Send offprint requests to: V. Caloi

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Contents

• 1. Introduction
• 2. Observations and data analysis
  • Star V441
  • Star V897
  • Star V1115
  • Star V1336
  • Star V1430
  • Star V1597
• 3. Stellar temperatures
  • 3.1. The metal content
  • 3.2. The reddening
  • 3.3. Spectral classification
  • 3.4. Fits with Kurucz models
  • Bright stars: V 15.5 mag
  • Faint stars: V 15.5
  • Star V1115
  • Star V3037
  • 3.5. Luminosities, gravities and masses
  • Gravities and masses
• 4. Evolutionary status and age spread
  • 4.1. The theoretical H-R diagram
  • 4.2. Mass distribution in the upper main sequence
  • 4.3. Space distribution of NGC 1850A and NGC 1850 members
  • 4.4. Star V3037, the HR diagram and the age of the main cluster
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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