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Astronomy and Astrophysics 404 (2003) 145-156
Bulge Microlensing Optical Depth from EROS 2 observations
C. Afonso1, 2, J N. Albert3, C. Alard4, J. Andersen, R. Ansari3, E. Aubourg1, 2, P. Bareyre1, 2, F. Bauer1, 2, J-P. Beaulieu5, G. Blanc1, 2, A. Bouquet1, S. Char, X. Charlot1, 2, F. Couchot3, C. Coutures1, 2, F. Derue1, 2, R. Ferlet5, P. Fouque6, J-F. Glicenstein1, 2, B. Goldman1, 2, A. Gould, D. Graff, M. Gros1, 2, J. Haissinski3, C. Hamache1, 2, J-C. Hamilton, D. Hardin1, 2, J. De Kat1, 2, A. Kim, T. Lasserre1, 2, L. Le Guillou1, 2, E. Lesquoy2, 5, C. Loup5, C. Magneville1, 2, B. Mansoux, J-B. Marquette5, E. Maurice7, A. Maury, A. Milsztajn1, 2, M. Moniez3, N. Palanque-Delabrouille1, 2, O. Perdereau3, L. prevot7, N. Regnault3, J. Rich1, 2, M. Spiro1, 2, P. Tisserand1, 2, A. Vidal-Madjar5, L. Vogroux1, 2, S. Zylberajch1, 2
For the EROS collaboration(s)
(2003)

We present a measurement of the microlensing optical depth toward the Galactic bulge based on the analysis of 15 contiguous1 square degrees fields centered on (l=2.5 deg, b=-4.0 deg) and containing 1.42 million clump-giant stars (belonging to the extended clump area) monitored during almost three bulge seasons by EROS (Experience de Recherche d'Objets Sombres). We find a microlensing optical depth towards the bulge tau_bulge=0.94 +/- 0.29 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.
1:  PCC - Physique Corpusculaire et Cosmologie - Collège de France
2:  DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
3:  LAL - Laboratoire de l'Accélérateur Linéaire
4:  DASGAL - Departement d'Astrophysique Stellaire et Galactique
5:  IAP - Institut d'Astrophysique de Paris
6:  LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
7:  LAM - Laboratoire d'Astrophysique de Marseille
Physics/Astrophysics/Cosmology and Extra-Galactic Astrophysics

Sciences of the Universe/Astrophysics
Fulltext link: 
http://fr.arXiv.org/abs/astro-ph/0303100