Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482
M. Zub, A. Cassan, D. Heyrovsky, P. Fouque, H.C. Stempels, M.D., Albrow, J.-P. Beaulieu, S. Brillant, G.W. Christie, N. Kains, S. Kozlowski,, D. Kubas, J. Wambsganss (From the PLANET, microFUN, OGLE Collaborations),, V. Batista, D.P. Bennett, K. Cook, C. Coutures, S. Dieters

TL;DR
This study measures limb-darkening in a red giant star during a microlensing event, providing empirical data that closely matches theoretical models and enhancing understanding of stellar atmospheres.
Contribution
It presents the first detailed limb-darkening measurements for a red giant in a microlensing event, validated against model predictions and using multi-band photometry and high-resolution spectra.
Findings
Measured limb-darkening coefficients in I, R, and broad filters
Confirmed stellar parameters with high-resolution spectra
Found excellent agreement between observations and models
Abstract
Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of their source star, as shown in this study. Methods: Our dense photometric coverage of the overall light curve and a proper microlensing modelling allow us to derive measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening coefficients in three bands, including standard Johnson-Cousins I and R, as well as in a broad clear filter. In particular, we discuss in detail the problems of multi-band and multi-site modelling on the expected precision of our results. We also obtained high-resolution UVES spectra as part of a ToO programme at ESO VLT from which we derive the source star's precise…
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