AGAPE, a microlensing search in the direction of M31: status report

The M31 galaxy in Andromeda is the nearest large galaxy after the Small and Large Magellanic Clouds. It is a giant galaxy, roughly 2 times as large as our Milky Way, and has its own halo. As pointed by some of us [1, 2] and independantly by A. Crotts [3], M31 provides a rich field of stars to search for MACHO's in galactic halos by gravitational microlensing [4]. M31 is a target complementary to the Magellanic Clouds used by the current experiments [5, 6]. It is complementary in that it allows to probe the halo of our galaxy in a direction very different from that of the LMC. Moreover, the fact that M31 has its own halo and is tilted with respect to the line of sight provides a very interesting signature [3] : assuming an approximately spherical halo for M31, the far side of the disk lies behind a larger amount of M31 dark matter, therefore more microlensing events are expected on the far side of the disk. Such an asymmetry could not be faked by variable stars.