Determination of stellar shape in microlensing event MOA 2002-BLG-33
  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 microarcsec. 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. 
N. J. Rattenbury, F. Abe, D. P. Bennett, I. A. Bond, J. J. Calitz, A.   Claret, K. H. Cook, Y. Furuta, A. Gal-Yam, J-F. Glic...