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We investigate $HST$/ACS and WFPC2 images at the positions of five candidate microlensing events from a large survey of variability in M31 (MEGA). Three closely match unresolved sources, and two produce only flux upper limits. All are confined to regions of the color-magnitude diagram where stellar variability is unlikely to be easily confused with microlensing. Red variable stars cannot explain these events (although background supernova are possible for two). If these lenses arise in M31s halo, they are due to masses $0.15 < m / M_odot < 0.49$ (95% certainty, for a $delta$-function mass distribution), brown dwarfs for disk lenses, and stellar masses for bulge lenses.
One of the possible astrophysical solutions to the galactic dark matter problem is the presence of a significant amount of ``dark compact objects (MACHOs) in galactic dark matter halos. MEGA (Microlensing Exploration of the Galaxy and Andromeda) trie
We present the first M31 candidate microlensing events from the Microlensing Exploration of the Galaxy and Andromeda (MEGA) survey. MEGA uses several telescopes to detect microlensing towards the nearby Andromeda galaxy, M31, in order to establish wh
This paper has been withdrawn.
This paper has been withdrawn.
We present the first results of the analysis of data collected during the 1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards the Andromeda galaxy (M31), aimed to the detection of gravitational microlensing effects as a pro