Astron. Astrophys. 339, 658-670 (1998)

AGAPEROS: searches for microlensing in the LMC with the pixel method

II. Selection of possible microlensing events

A.-L. Melchior ^{1, 2}, C. Afonso ³, R. Ansari ⁴, É. Aubourg ³, P. Baillon ⁵, P. Bareyre ³, F. Bauer ³, J.-Ph. Beaulieu ⁶, A. Bouquet ², S. Brehin ³, F. Cavalier ⁴, S. Char ⁷, F. Couchot ⁴, C. Coutures ³, R. Ferlet ⁶, J.  Fernandez ⁷, C. Gaucherel ³, Y. Giraud-Héraud ², J.-F. Glicenstein ³, B. Goldman ³, P. Gondolo ^{2, 8}, M. Gros ³, J. Guibert ⁹, D. Hardin ³, J. Kaplan ², J. de Kat ³, M. Lachièze-Rey ³, B. Laurent ³, É. Lesquoy ³, Ch. Magneville ³, B. Mansoux ⁴, J.-B. Marquette ⁶, E. Maurice ¹⁰, A. Milsztajn ³, M. Moniez ⁴, O. Moreau ⁹, L. Moscoso ³, N. Palanque-Delabrouille ³, O. Perdereau ⁴, L. Prévôt ¹⁰, C. Renault ³, F. Queinnec ³, J. Rich ³, M. Spiro ³, A. Vidal-Madjar ⁶, L. Vigroux ³ and S. Zylberajch <sup>3

1</sup> Astronomy Unit, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK
² Laboratoire de Physique Corpusculaire et Cosmologie (UMR 7535), Collège de France, F-75 231 Paris Cedex 05, France
³ CEA, DSM, DAPNIA, Centre d'Études de Saclay, F-91191 Gif-sur-Yvette Cedex, France
⁴ Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université Paris-Sud, B.P. 34, F-91898 Orsay Cedex, France
⁵ CERN, CH-1211 Genève 23, Switzerland
⁶ Institut d'Astrophysique de Paris, CNRS, 98 bis Boulevard Arago, F-75 014 Paris, France
⁷ Universidad de la Serena, Faculdad de Ciencias, Departemento de Fisica, Casilla 554, La Serena, Chile
⁸ Max-Planck-Institut für Physik, Föhringer Ring 6, D-80 805 München, Germany
⁹ Centre d'Analyse des Images de l'INSU, Observatoire de Paris, 61 avenue de l'Observatoire, F-75014 Paris, France
¹⁰ Observatoire de Marseille, 2 place Le Verrier, F-13 248 Marseille Cedex 04, France

Received 4 May 1998 / Accepted 9 September 1998

Abstract

We apply the pixel method of analysis (sometimes called "pixel lensing") to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method, applied to crowded fields, should detect 10 to 20 times more microlensing events for Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1 - 0.5 , a pixel analysis of the three-year EROS-1 data set covering would yield events.

Key words: methods: data analysis techniques: photometric galaxies: Magellanic Clouds dark matter gravitational lensing

Send offprint requests to: A.L.Melchior@qmw.ac.uk

SIMBAD Objects

Contents

• 1. Introduction
  • Microlensing selection with the pixel method
• 2. A useful tool: mock super-pixel light curves with microlensing events
  • 2.1. Physical ingredients
  • 2.2. Minimal requirements for simulated microlensing events
  • 2.3. Preliminary estimates
    • 2.3.1. Number of expected events
    • 2.3.2. Effective number of monitored stars
  • 2.4. Model of the data
• 3. Selection of microlensing events
  • 3.1. At least one significant variation
  • 3.2. No significant second bump
  • 3.3. Correlation between the two colours
• 4. Colour magnitude diagram
  • 4.1. Magnitude determination
  • 4.2. Discussion
  • 4.3. Final cut on the colour magnitude diagram
• 5. Results
  • 5.1. Detection efficiencies for pixel monitoring
  • 5.2. Comparison with star monitoring
• 6. Perspectives for the Magellanic Clouds
  • 6.1. The whole EROS-1 CCD data set
  • 6.2. Other sources of data
  • 6.3. Pixel method
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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