Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-07-11
Astronomy and Astrophysics
Astrophysics
18 pages, 8 figures. to appear in the proceedings of the Marcel Grossmann Meeeting X
Scientific paper
10.1017/S1743921305002140
The nature and the location of the lenses discovered in the microlensing surveys done so far towards the LMC remain unclear. Motivated by these questions we computed the optical depth for the different intervening populations and the number of expected events for self-lensing, using a recently drawn coherent picture of the geometrical structure and dynamics of the LMC. By comparing the theoretical quantities with the values of the observed events it is possible to put some constraints on the location and the nature of the MACHOs. Clearly, given the large uncertainties and the few events at disposal it is not yet possible to draw sharp conclusions, nevertheless we find that up to 3-4 MACHO events might be due to lenses in LMC, which are most probably low mass stars, but that hardly all events can be due to self-lensing. The most plausible solution is that the events observed so far are due to lenses belonging to different intervening populations: low mass stars in the LMC, in the thick disk, in the spheroid and some true MACHOs in the halo of the Milky Way and the LMC itself. We report also on recent results of the SLOTT-AGAPE and POINT-AGAPE collaborations on a search for microlensing events in direction of the Andromeda galaxy, by using the pixel method. The detection of 4 microlensing events, some likely to be due to self--lensing, is discussed. One microlensing light curve is shown to be compatible with a binary lens. The present analysis still does not allow us to draw conclusions on the MACHO content of the M31 galaxy.
Calchi Novati Sebastiano
Jetzer Philippe
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