Astron. Astrophys. 329, 522-537 (1998)

Search for planetary mass objects
in the Galactic halo through microlensing ^*

C. Renault¹, É. Aubourg¹, P. Bareyre¹, S. Brehin¹, M. Gros ¹, M. Lachièze-Rey¹, B. Laurent¹, É. Lesquoy¹, C. Magneville¹, A. Milsztajn¹, L. Moscoso¹, N. Palanque-Delabrouille¹, F. Queinnec¹, J. Rich¹, M. Spiro¹, L. Vigroux¹, S. Zylberajch¹, R. Ansari², F. Cavalier², M. Moniez², J.-Ph. Beaulieu ³, R. Ferlet³, Ph. Grison³, A. Vidal-Madjar³, J. Guibert ⁴, O. Moreau⁴, É. Maurice⁵, L. Prévôt⁵, C. Gry⁶, S. Char⁷ and J. Fernandez⁷
The EROS collaboration

¹ CEA, DSM, DAPNIA, Centre d'Études de Saclay, F-91191 Gif-sur-Yvette Cedex, France
² Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université Paris-Sud, F-91405 Orsay Cedex, France
³ Institut d'Astrophysique de Paris, CNRS, 98 bis Boulevard Arago, F-75014 Paris, France
⁴ Centre d'Analyse des Images de l'INSU, Observatoire de Paris, 61 avenue de l'Observatoire, F-75014 Paris, France
⁵ Observatoire de Marseille, 2 place Le Verrier, F-13248 Marseille Cedex 04, France
⁶ Laboratoire d'Astronomie Spatiale de Marseille, Traverse du Siphon, Les Trois Lucs, F-13120 Marseille, France
⁷ Universidad de la Serena, Faculdad de Ciencias, Departemento de Fisica, Casilla 554, La Serena, Chile

Received 6 May 1997 / Accepted 11 July 1997

Abstract

We present final results from a search for gravitational microlensing of stars in the Magellanic Clouds by very light machos (MAssive Compact Halo Objects) in the Galactic Halo. The EROS programme used a CCD camera devoted to the detection of events with a duration ranging from 15 minutes to a few days; none of the 350,000 light curves exhibits a form which is consistent with a microlensing event. Using our detection efficiency, largely affected by the finite size of the source and blending effects at the lowest durations, and different models of the Galaxy, we can exclude planetary mass objects as a major constituent of the dark Halo.

Key words: Galaxy: halo; kinematics and dynamics; stellar content dark matter gravitational lensing

* Based on observations made at the European Southern Observatory, La Silla, Chile.

Send offprint requests to: cecile.renault@cea.fr

SIMBAD Objects

Contents

• 1. Introduction
• 2. Expected signal
  • 2.1. Point-like case
  • 2.2. Finite size of the source
  • 2.3. Blending
  • 2.4. Other effects
  • 2.5. Expected microlensing rate
  • 2.6. Summary
• 3. From data to light curves
  • 3.1. Data taking
  • 3.2. From images to raw fluxes
  • 3.3. Photometric alignment and accuracy
  • 3.4. Absolute photometric calibration
  • 3.5. Summary
• 4. Rejection of poor quality data
  • 4.1. Usable images
  • 4.2. Usable measurements
  • 4.3. Usable stars
  • 4.4. Summary
• 5. Analysis
  • 5.1. Properties of the signal
  • 5.2. Definition of a variation
  • 5.3. Characterisation of a light curve
  • 5.4. Simplified simulation
  • 5.5. Selection criteria
  • 5.6. Individual inspection of remaining light curves
  • 5.7. Number of detected events
• 6. Complete simulation and detection efficiency
  • 6.1. Finite source size
  • 6.2. Blending effect
  • 6.3. Detection efficiency
• 7. Expected number of events
  • 7.1. Computation of
  • 7.2. Models of the Galaxy
  • 7.3. Contribution of halo deflectors
  • 7.4. Contributions of non-halo objects
  • 7.5. Summary
• 8. Constraints on the halo
  • 8.1. The exclusion diagram
  • 8.2. EROS limits
  • 8.3. Comparing EROS and MACHO results
• 9. Conclusion
• Appendix
  • Appendix A: detection efficiency
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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