Astron. Astrophys. 326, 1-12 (1997)

The DUO single lens candidates

I. The 1994 campaign

C. Alard ^{1, 2, 3} and J. Guibert <sup>1, 2

1</sup> DEMIRM,Observatoire de Paris, 61 Avenue de l'observatoire, F-75014 Paris, France
² Centre d'Analyse des Images de l'INSU, Batiment Perrault, Observatoire de Paris, 61 Avenue de l'Observatoire, F-75014, Paris, France
³ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

Received 26 February 1997 / Accepted 23 April 1997

Abstract

The microlensing candidates found in the first DUO season are presented here. Statistical tests show that these candidates stand well above the noise distribution. The analysis of their colours shows in addition that they are not related with pulsating variable stars. We also conclude that they are unlikely to be associated with cataclysmic variables. Unless a new class of variable objects has been discovered here, microlensing appears as the best explanation of their light curves. The latitude distribution of these candidates is different from the distribution of the other stars: it shows a large gradient which is well reproduced by a microlensing model. We conclude that this is a good signature of microlensing. The large fraction of short duration events among these candidates is rather puzzling, and cannot be reproduced, within a standard microlensing model, without a large number of brown dwarfs. However, a more sophisticated model including the amplification of unresolved stars can well reproduce the observed rates without any brown dwarfs. Consequently, we demonstrate with these data the great importance of modeling the amplification rates of unresolved stars. It is also concluded that any satisfactory study of the mass function at the faint end, should include this kind of contribution.

Key words: dark matter graviatational lensing stars: low-mass, brown dwarfs stars: binaries stars: planetary systems

Send offprint requests to: C. Alard

Contents

• 1. Introduction
• 2. Data reduction
  • 2.1. Plate scanning
  • 2.2. Photometric reduction
• 3. Identification of the microlensing candidates
  • 3.1. Selection criteria
    • 3.1.1. Pre-selection of the light curves
    • 3.1.2. Chi-square analysis of the pre-selected light curves
  • 3.2. A study of the noise distribution
  • 3.3. Analysis of the remaining light curves
• 4. The light curves of the candidates
• 5. Can these candidates be variable stars?
  • 5.1. Examples of dwarf novae found by DUO
  • 5.2. The spatial distribution of the candidates
  • 5.3. Estimation of the efficiency
• 6. Comparison with a model
  • 6.1. The model
    • 6.1.1. The galactic components
    • 6.1.2. The mass function
  • 6.2. Predictions of the model
  • 6.3. Comparison with the data
• 7. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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