Detection of M31 Binaries via High‐Cadence Pixel‐lensing Surveys

D. Kim, S.‐J. Chung, M. J. Darnley, J. P. Duke, A. Gould, C. Han, M. A. Ibrahimov, M. Im, Y.‐B. Jeon, R. G. Karimov, E. Kerins, C.‐U. Lee (+2 others)
2007 Astrophysical Journal  
The Angstrom Project is using a distributed network of two-meter class telescopes to conduct a high cadence pixel-lensing survey of the bulge of the Andromeda Galaxy (M31). With the expansion of global telescope network, the detection efficiency of pixel-lensing surveys is rapidly improving. In this paper, we estimate the detection rate of binary lens events expected from high-cadence pixel-lensing surveys toward M31 such as the Angstrom Project based on detailed simulation of events and
more » ... f events and application of realistic observational conditions. Under the conservative detection criteria that only high signal-to-noise caustic-crossing events with long enough durations between caustic crossings can be firmly identified as binary lens events, we estimate that the rate would be Γ_ b∼ (7-15)f_ b(N/50) per season, where f_ b is the fraction of binaries with projected separations of 10^-3 AU<d̃<10^3 AU out of all lenses and N is the rate of stellar pixel-lensing events. We find that detected binaries would have mass ratios distributed over a wide range of q≳ 0.1 but with separations populated within a narrow range of 1 AU≲d̃≲ 5 AU. Implementation of an alert system and subsequent follow-up observations would be important not only for the increase of the binary lens event rate but also for the characterization of lens matter.
doi:10.1086/519919 fatcat:dptla2t75bgnziiggbldvrysoa