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PLANET observations of microlensing event OGLE-1999-BUL-23: limb darkening measurement of the source star

M. D. Albrow·J. An·J. -P. Beaulieu·J. A. R. Caldwell·D. L. DePoy·M. Dominik·B. S. Gaudi·A. Gould·J. Greenhill·K. Hill·S. Kane·R. Martin·J. Menzies·R. W. Pogge·K. R. Pollard·P. D. Sackett·K. C. Sahu·P. Vermaak·R. Watson·A. Williams
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Abstract

We present PLANET observations of OGLE-1999-BUL-23, a binary-lens microlensing event towards the Galactic bulge. PLANET observations in the I and V bands cover the event from just before the first caustic crossing until the end of the event. In particular, a densely-sampled second caustic crossing enables us to derive the linear limb-darkening coefficients of the source star; c_V = 0.786^{+0.080}_{-0.078} and c_I = 0.632^{+0.047}_{-0.037}. Combined analysis of the light curve and the color-magnitude diagram suggests that the source star is a G/K subgiant in the Galactic bulge (T_eff = 4800 K). The resulting linear limb-darkening coefficient of the source is consistent with theoretical predictions, although it is likely that non-linearity of the stellar surface brightness profile complicates the interpretation, especially for the I band. The global light curve fit to the data indicates that the event is due to a binary lens of a mass ratio q = 0.39 and a projected separation d = 2.42. The lens/source relative proper motion is (22.8 +_ 1.5) km/s/kpc, typical of bulge/bulge or bulge/disk events.

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M. D. Albrow, J. An, J. -P. Beaulieu, J. A. R. Caldwell, D. L. DePoy, M. Dominik, B. S. Gaudi, A. Gould, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R. W. Pogge, K. R. Pollard, P. D. Sackett, K. C. Sahu, P. Vermaak, R. Watson, A. Williams. 2000-11-01. PLANET observations of microlensing event OGLE-1999-BUL-23: limb darkening measurement of the source star. https://doi.org/10.1086/319437

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