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Astron. Astrophys. 332, 1-9 (1998)

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Microlensing towards the Small Magellanic Cloud EROS 2 first year survey *

N. Palanque-Delabrouille 1, 9, C. Afonso 1, J.N. Albert 2, J. Andersen 6, R. Ansari 2, É. Aubourg 1, P. Bareyre 1, 4, F. Bauer 1, J.P. Beaulieu 5, A. Bouquet 4, S. Char 7, X. Charlot 1, F. Couchot 2, C. Coutures 1, F. Derue 2, R. Ferlet 5, J.F. Glicenstein 1, B. Goldman 1, 10, 11, A. Gould 1, 8, D. Graff 1, M. Gros 1, J. Haissinski 2, J.C. Hamilton 4, D. Hardin 1, J. de Kat 1, É. Lesquoy 1, C. Loup 5, C. Magneville 1, B. Mansoux 2, J.B. Marquette 5, É. Maurice 3, A. Milsztajn 1, M. Moniez 2, O. Perdereau 2, L. Prévot 3, C. Renault 1, J. Rich 1, M. Spiro 1, A. Vidal-Madjar 5, L. Vigroux 1 and S. Zylberajch The EROS collaboration 1

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 Observatoire de Marseille, 2 pl. Le Verrier, F-13248 Marseille Cedex 04, France
4 Collège de France, Laboratoire de Physique Corpusculaire, IN2P3 CNRS, 11 pl. Marcellin Berthelot, F-75231 Paris Cedex, France
5 Institut d'Astrophysique de Paris, INSU CNRS, 98 bis Boulevard Arago, F-75014 Paris, France
6 Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
7 Universidad de la Serena, Facultad de Ciencias, Departamento de Fisica, Casilla 554, La Serena, Chile
8 Department of Astronomy, Ohio State University, Columbus, OH 43210, USA
9 Enrico Fermi Institute, University of Chicago, 5460 South Ellis Avenue, Chicago, IL 60637, USA
10 Department Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile
11 European Southern Observatory, Casilla 19001, Santiago 19, Chile

Received 31 October 1997 / Accepted 4 December 1997

Abstract

We present here an analysis of the light curves of 5.3 million stars in the Small Magellanic Cloud observed by EROS (Expérience de Recherche d'Objets Sombres). One star exhibits a variation that is best interpreted as due to gravitational microlensing by an unseen object. This candidate was also reported by the MACHO collaboration. Once corrected for blending, the Einstein radius crossing time is 123 days, corresponding to lensing by a Halo object of [FORMULA]. The maximum magnification is a factor of 2.6. The light curve also displays a periodic modulation with a 2.5% amplitude and a period of 5.1 days. Parallax analysis of the candidate indicates that a Halo lens would need to have a mass of at least [FORMULA], although a lens in the SMC could have a mass as low as [FORMULA]. We estimate the optical depth for microlensing towards the SMC due to this event to be [FORMULA], with an uncertainty dominated by Poisson statistics. We show that this optical depth corresponds to about half that expected for a spherical isothermal Galactic Halo comprised solely of such objects, and that it is consistent with SMC self-lensing if the SMC is elongated along the line-of-sight by at least 5 kpc.

Key words: Galaxy: halo – Galaxy: kinematics and dynamics – Galaxy: stellar content – Magellanic Clouds – dark matter – gravitational lensing

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

Send offprint requests to: Nathalie.Delabrouille@cea.fr

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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