Determination of stellar shape in microlensing event MOA 2002-BLG-33
Bennett, D. P.; Cook, K. H.; Gal-Yam, A.; Hauschildt, P. H.; Maoz, D.; Sumi, T.; Claret, A.; Ofek, E. O.; Meintjes, P. J.; Terndrup, D. M.; Moniez, M.; Bond, I. A.; Abe, F.; Matsubara, Y.; Muraki, Y.; Sullivan, D. J.; Tristram, P. J.; Sako, T.; Yock, P. C. M.; Hearnshaw, J. B.; Rattenbury, N. J.; Kilmartin, P. M.; Masuda, K.; Yanagisawa, T.; Rhie, S. H.; Calitz, J. J.; Furuta, Y.; Glicenstein, J. -F.; Kurata, Y.; Noda, S.; Okajima, K.; Philpott, L.; Wood, J.
United Kingdom, Japan, United States, New Zealand, South Africa, Spain, France, Germany, Israel
Abstract
We report a measurement of the shape of the source star in microlensing event MOA 2002-BLG-33. The lens for this event was a close binary whose centre-of-mass passed almost directly in front of the source star. At this time, the source star was closely bounded on all sides by a caustic of the lens. This allowed the oblateness of the source star to be constrained. We found that a/b = 1.02+0.04-0.02 where a and b are its semi-major and semi-minor axes respectively. The angular resolution of this measurement is approximately 0.04 μ{arcsec}. We also report HST images of the event that confirm a previous identification of the source star as an F8-G2 turn-off main-sequence star.