Bulge microlensing optical depth from EROS 2 observations

Free access article

Issue		A&A Volume 404, Number 1, June II 2003


Page(s)		145 - 156
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20030307

A&A 404, 145-156 (2003)
DOI: 10.1051/0004-6361:20030307

Bulge microlensing optical depth from EROS 2 observations $^{\bullet}$

C. Afonso^{1, 2, 3}, J. N. Albert⁴, C. Alard⁵, J. Andersen⁶, R. Ansari⁴, É. Aubourg¹, P. Bareyre^{1, 2}, F. Bauer¹, J. P. Beaulieu⁷, G. Blanc¹, A. Bouquet², S. Char⁸, X. Charlot¹, F. Couchot⁴, C. Coutures¹, F. Derue^{1, 4}, R. Ferlet⁷, P. Fouqué^{9, 10}, J. F. Glicenstein¹, B. Goldman^{1, 2, 3}, A. Gould^{2, 11}, D. Graff¹¹, M. Gros¹, J. Haissinski⁴, C. Hamadache¹, J. C. Hamilton², D. Hardin¹, J. de Kat¹, A. Kim², T. Lasserre¹, L. LeGuillou¹, É. Lesquoy^{1, 7}, C. Loup⁷, C. Magneville¹, B. Mansoux⁴, J. B. Marquette⁷, É. Maurice¹², A. Maury¹⁰, A. Milsztajn¹, M. Moniez⁴, N. Palanque-Delabrouille¹, O. Perdereau⁴, L. Prévot¹², N. Regnault⁴, J. Rich¹, M. Spiro¹, P. Tisserand¹, A. Vidal-Madjar⁷, L. Vigroux¹ and S. Zylberajch¹

¹ CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette Cedex, France
² Collège de France, Physique Corpusculaire et Cosmologie, IN2P3 CNRS, 11 Pl. M. Berthelot, 75231 Paris Cedex, France
³ Department of Astronomy, New Mexico State University, Las Cruces, NM 88003-8001, USA
⁴ Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université de Paris-Sud, 91405 Orsay Cedex, France
⁵ DASGAL, INSU-CNRS, 77 avenue de l'Observatoire, 75014 Paris, France
⁶ Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁷ Institut d'Astrophysique de Paris, INSU CNRS, 98bis boulevard Arago, 75014 Paris, France
⁸ Universidad de la Serena, Facultad de Ciencias, Departamento de Fisica, Casilla 554, La Serena, Chile
⁹ Observatoire de Paris, LESIA, 92195 Meudon Cedex, France
¹⁰ European Southern Observatory (ESO), Casilla 19001, Santiago 19, Chile
¹¹ Department of Astronomy, Ohio State University, Columbus, OH 43210, USA
¹² Observatoire de Marseille, 2 Pl. Le Verrier, 13248 Marseille Cedex 04, France

(Received 22 August 2002 / Accepted 28 February 2003)

Abstract
We present a measurement of the microlensing optical depth toward the Galactic bulge based on the analysis of 15 contiguous $1\,\rm deg^2$ fields centered on $(l=2.\hskip-2pt^\circ 5, b=-4.\hskip-2pt^\circ 0)$ and containing $N_*=1.42\times 10^{6}$ clump-giant stars (belonging to the extended clump area) monitored during almost three bulge seasons by EROS (Expérience de Recherche d'Objets Sombres). We find $\tau_{\rm bulge}=0.94\pm 0.29\times 10^{-6}$ averaged over all fields, based on 16 microlensing events with clump giants as sources. This value is substantially below several other determinations by the MACHO and OGLE groups and is more in agreement with what is expected from axisymmetric and non-axisymmetric bulge models.

Key words: Galaxy: stellar content -- Galaxy: structure -- gravitational lensing

Offprint request: C. Afonso, afonso@hep.saclay.cea.fr

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