Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482

M. Zub , A. Cassan (1) , D. Heyrovský , P. Fouqué (2) , H. C. Stempels , M. D. Albrow , J. -P. Beaulieu (1) , S. Brillant , G. W. Christie , N. Kains , S. Kozłowski , D. Kubas (1) , J. Wambsganss , V. Batista (1) , D. P. Bennett , K. Cook , C. Coutures (1) , S. Dieters (1) , M. Dominik , D. Dominis Prester , J. Donatowicz , J. Greenhill , K. Horne , U. G. Jørgensen , S. R. Kane , J. -B. Marquette (1) , R. Martin , J. Menzies , K. R. Pollard , K. C. Sahu , C. Vinter , A. Williams , A. Gould , D. L. Depoy , A. Gal-Yam , B. S. Gaudi , C. Han , Y. Lipkin , D. Maoz , E. O. Ofek , B. -G. Park , R. W. Pogge , J. Mccormick , A. Udalski , M. K. Szymański , M. Kubiak , G. Pietrzyński , I. Soszyński , O. Szewczyk , Ł. Wyrzykowski

1 IAP - Institut d'Astrophysique de Paris
2 LATT - Laboratoire Astrophysique de Toulouse-Tarbes

Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event that 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-482source 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 fundamental parameters.
Results: From the high-resolution UVES spectra, we find that OGLE 2004-BLG-482's source star is a red giant of MK type a bit later than M3, with T_eff = 3667 ± 150 K, log g = 2.1 ± 1.0 and an assumed solar metallicity. This is confirmed by an OGLE calibrated colour-magnitude diagram. We then obtain from a detailed microlensing modelling of the light curve linear limb-darkening coefficients that we compare to model-atmosphere predictions available in the literature, and find a very good agreement for the I and R bands. In addition, we perform a similar analysis using an alternative description of limb darkening based on a principal component analysis of ATLAS limb-darkening profiles, and also find a very good agreement between measurements and model predictions.

Partly based on observations made at ESO (073.D-0575A).

Keywords: gravitational lensing: micro; stars: atmospheres; techniques: high angular resolution; stars: individual: OGLE 2004-BLG-482

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

M. Zub, A. Cassan, D. Heyrovský, P. Fouqué, H. C. Stempels, et al.. Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482. Astronomy and Astrophysics - A&A, 2011, 525, ⟨10.1051/0004-6361/200912007⟩. ⟨insu-03646107⟩