Observational Limits on Machos in the Galactic Halo

EROS collaboration, C. Renault, C. Afonso, E. Aubourg, P. Bareyre, F. Bauer, S. Brehin, C. Coutures, C. Gaucherel, J. F. Glicenstein, B. Goldman, M. Gros, D. Hardin, J. de Kat, M. Lachieze-Rey, B. Laurent, E. Lesquoy, C. Magneville, A. Milsztajn, L. Moscoso, N. Palanque-Delabrouille, F. Queinnec, J. Rich, M. Spiro, L. Vigroux, S. Zylberajch, R. Ansari, F. Cavalier, F. Couchot, B. Mansoux, M. Moniez, O. Perdereau, J. -Ph. Beaulieu, R. Ferlet, Ph. Grison, A. Vidal-Madjar, J. Guibert, O. Moreau, E. Maurice, L. Prevot, C. Gry, S. Char, J. Fernandez

Published 1996-12-10, updated 1997-03-10Version 2

We present final results from the first phase of the EROS search for gravitational microlensing of stars in the Magellanic Clouds by unseen deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to events with time scales between 15 minutes and 200 days corresponding to deflector masses in the range 1.e-7 to a few solar masses. Two events were observed that are compatible with microlensing by objects of mass of about 0.1 Mo. By comparing the results with the expected number of events for various models of the Galaxy, we conclude that machos in the mass range [1.e-7, 0.02] Mo make up less than 20% (95% C.L.) of the Halo dark matter.