OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star
Abstract
Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M=(c^2/4G)\tilde r_E \theta_E and so requires the measurement of both the angular Einstein radius, \theta_E, and the projected Einstein radius, \tilde r_E. Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (I_min=10.3), high-magnification (A_max = 170) microlensing event. Pronounced finite source effects permit a measurement of \theta_E = 650 uas. Although the timescale of the event is only t_E = 38 days, one can still obtain weak constraints on the microlens parallax: 4.4 AU < \tilde r_E < 18 AU at the 1 \sigma level. Together these two parameter measurements yield a range for the lens mass of 0.36 M_sun < M < 1.48 M_sun. As was the case for MACHO-LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements.
Cite
@article{arxiv.astro-ph/0404394,
title = {OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star},
author = {Guangfei Jiang and D. L. DePoy and A. Gal-Yam and B. S. Gaudi and A. Gould and C. Han and Y. Lipkin and D. Maoz and E. O. Ofek and B. -G. Park and R. W. Pogge and A. Udalski and M. Kubiak and M. K. Szymanski and O. Szewczyk and K. Zebrun and L. Wyrzykowski and I. Soszynski and G. Pietrzynski and M. D. Albrow and J. -P. Beaulieu and J. A. R. Caldwell and A. Cassan and C. Coutures and M. Dominik and J. Donatowicz and P. Fouque and J. Greenhill and K. Hill and K. Horne and S. F. Jorgensen and U. G. Jorgensen and S. Kane and D. Kubas and R. Martin and J. Menzies and K. R. Pollard and K. C. Sahu and J. Wambsganss and R. Watson and A. Williams},
journal= {arXiv preprint arXiv:astro-ph/0404394},
year = {2009}
}
Comments
Submitted to ApJ, 23 pages including 3 figures