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

journal contribution
posted on 2023-05-16, 12:55 authored by Albrow, MD, An, J, Jean-Philippe BeaulieuJean-Philippe Beaulieu, Caldwell, JAR, DePoy, DL, Dominik, M, Gaudi, BS, Gould, A, Greenhill, JG, Kym HillKym Hill, Kane, S, Martin, R, Menzies, J, Pogge, RW, Pollard, KR, Sackett, PD, Sahu, KC, Vermaak, P, Watson, RD, Williams, A
We present PLANET observations of OGLE-1999-BUL-23, a binary-lens microlensing event toward 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 nonlinearity 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 -1 kpc -1, typical of bulge/bulge or bulge/disk events.


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The Astrophysical Journal








School of Natural Sciences


The University of Chicago Press

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