Astron. Astrophys. 336, 883-894 (1998)

The luminosity function of white dwarfs and M dwarfs using dark nebulae as opaque outer screens ^*

L. Festin

Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden (leif@astro.uu.se)

Received 28 January 1998 / Accepted 9 June 1998

Abstract

By using dark nebulae as opaque outer screens, the luminosity function of white dwarfs and M dwarfs has been studied. High-extinction areas towards the Orion A, Serpens and Oph cloud complexes were observed, covering a volume corresponding to 464 pc³ in the solar neighbourhood, complete to . Foreground stars were selected by VRI photometry and photometric parallaxes.

The resulting foreground sample consists of 21 M dwarfs and 7 white dwarfs. The derived M-dwarf luminosity function is consistent with previous studies, showing no substantial upturn beyond . The 7 white dwarfs imply a local density of 0.013 () pc^-3 (15 % of the dynamical mass in the solar neighbourhood) supporting other recent results but obtained with a completely different method.

For the clouds, foreground-star data were used to derive independent cloud distances, while the background stars and a simple model of the Milky Way gave reliable cloud extinctions.

Key words: stars: late-type; low-mass; brown dwarfs; luminosity function; mass function; white dwarfs Galaxy: solar neighbourhood; stellar content

* Based on observations collected at the European Southern Observatory (ESO), La Silla, Chile and at the Nordic Optical Telescope (NOT), La Palma

Send offprint requests to: L. Festin

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Contents

• 1. Introduction
• 2. Selecting target clouds
  • 2.1. Cloud distances
• 3. Observations and reductions
  • 3.1. Complementary NOT observations
• 4. Star counts and cloud extinctions
  • 4.1. Orion A
  • 4.2. Serpens and Oph
• 5. Selecting foreground stars
  • 5.1. Colour-colour analysis
  • 5.2. Photometric parallaxes
    • 5.2.1. M dwarfs
    • 5.2.2. White dwarfs
    • 5.2.3. Spectroscopic confirmation of white dwarfs
• 6. Constraints on foreground candidates from other surveys
• 7. The luminosity function
  • 7.1. M dwarfs, main sequence
    • 7.1.1. Lost companions
  • 7.2. White dwarfs
• 8. Dicussion, comparison to other works
  • 8.1. The Jarrett paper
  • 8.2. White dwarfs
• 9. Conclusions and future prospects
• Acknowledgements
• Appendix A: the observed areas
• References

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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