MACHO 96-LMC-2: Lensing of a Binary Source in the Large Magellanic Cloud and Constraints on the Lensing Object

摘要: We present photometry and analysis of the microlensing alert MACHO 96-LMC-2 (event LMC-14 in an earlier paper). This event was initially detected by Alert System subsequently monitored Global Microlensing Network (GMAN). The ~3% provided GMAN follow-up effort reveals a periodic modulation light curve. attribute this to binarity lensed source. fits rotating binary source magnified single lens converge on two minima, separated Δχ2 ~ 1. most significant fit X1 predicts primary which contributes ~100% light, dark secondary, orbital period (T) ~9.2 days. second X2 yields with stars roughly equal mass luminosity T = 21.2 Observations made Hubble Space Telescope (HST) resolve stellar neighbors contribute object's baseline brightness. actual object appears lie upper LMC main sequence. estimate component system, M 2 M☉. helps determine physical size orbiting system allows measurement proper motion. For preferred model X1, we explore range companions assuming 0.1 M☉ 1.4 objects models X1a X1b, respectively. find velocities projected these 18.3 ± 3.1 km s-1 X1b 188 32 s-1. In both cases, likelihood suggests is over Galactic halo lens, although only marginally so X1b. also 39.6 6.1 s-1, where for location strongly dominated disk. all consistent that dwarf. Additional spectra are necessary further constrain and/or refine derived properties lensing object. self-lensing rate contributed rates. Thus, even if disk, it does not rule out possibility microlenses altogether. Finally, emphasize unique capability spectroscopic observations known microlensed stars, combined nondetection effects, locate lenses halo.