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OGLE 2004-BLG-254: a K3 III Galactic Bulge Giant spatially resolved by a single microlens

A. Cassan, J. -P. Beaulieu, P. Fouque, S. Brillant, M. Dominik, J. Greenhill, D. Heyrovsky, K. Horne, U. G. Jorgensen, D. Kubas, H. C. Stempels, C. Vinter, M. D. Albrow, D. Bennett, J. A. R. Caldwell, J. J. Calitz, K. Cook, C. Coutures, D. Dominis, J. Donatowicz, K. Hill, M. Hoffman, S. Kane, J. -B. Marquette, R. Martin, P. Meintjes, J. Menzies, V. R. Miller, K. R. Pollard, K. C. Sahu, J. Wambsganss, A. Williams, A. Udalski, M. K. Szymanski, M. Kubiak, G. Pietrzynski, I. Soszynski, K. Zebrun, O. Szewczyk, L. Wyrzykowski

astro-pharXiv:astro-ph/0609290

Abstract

We present an analysis of OGLE 2004-BLG-254, a high-magnification and relatively short duration microlensing event in which the source star, a Bulge K3-giant, has been spatially resolved by a point-like lens. We have obtained dense photometric coverage of the event light curve with OGLE and PLANET telescopes, as well as a high signal-to-noise ratio spectrum taken while the source was still magnified by 20, using the UVES/VLT spectrograph. Our dense coverage of this event allows us to measure limb darkening of the source star in the I and R bands. We also compare previous measurements of linear limb-darkening coefficients involving GK-giant stars with predictions from ATLAS atmosphere models. We discuss the case of K-giants and find a disagreement between limb-darkening measurements and model predictions, which may be caused by the inadequacy of the linear limb-darkening law.

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