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

¹ Astronomisches Rechen-Institut (ARI), Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12–14, 69120 Heidelberg, Germany
e-mail: zub@ari.uni-heidelberg.de
² International Max-Planck-Research School for Astronomy & Cosmic Physics at the University of Heidelberg, Germany
³ Institute of Astronomy, University of Zielona Góra, Lubuska st. 2, 65-265 Zielona Góra, Poland
⁵ Institut d’Astrophysique de Paris, UMR 7095 CNRS – Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁶ Institute of Theoretical Physics, Charles University, V Holešovičkách 2, 18000 Prague, Czech Republic
⁷ LATT, Université de Toulouse, CNRS, 31400 Toulouse, France
⁸ Department of Physics and Astronomy, Box 516, 751 20 Uppsala, Sweden
⁹ University of Canterbury, Department of Physics & Astronomy, Private Bag 4800, Christchurch, New Zealand
¹⁰ European Southern Observatory (ESO), Casilla 19001, Vitacura 19, Santiago, Chile
¹¹ Auckland Observatory, PO Box 24-197, Auckland, New Zealand
¹³ University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
¹⁴ Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
¹⁵ University of Notre Dame, Physics Department, 225 Nieuwland Science Hall, Notre Dame, IN 46530, USA
¹⁶ Institute of Geophysics and Planetary Physics, L-413, Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94550, USA
¹⁷ Department of Physics, University of Rijeka, Omladinska 14, 51000 Rijeka, Croatia
¹⁸ Technical University of Vienna, Dept. of Computing, Wiedner Hauptstrasse 10, Vienna, Austria
¹⁹ University of Tasmania, Physics Department, GPO 252C, Hobart, Tasmania 7001, Australia
²⁰ Niels Bohr Institute and Centre for Star and Planet Formation, Juliane Mariesvej 30, 2100 Copenhagen, Denmark
²¹ NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue Pasadena, CA 91125, USA
²² Perth Observatory, Walnut Road, Bickley, Perth 6076, Australia
²³ South African Astronomical Observatory, PO Box 9 Observatory 7935, South Africa
²⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁵ Astrophysics Group, Faculty of Physics, Weizmann Institute of Science, Rehovot 76100, Israel
²⁶ Department of Physics, Institute for Basic Science Research, Chungbuk National University, Chongju 361-763, Korea
²⁷ School of Physics and Astronomy and the Wise Observatory, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel Aviv, 69978, Israel
²⁸ School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv, 69978, Israel
²⁹ Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA, USA
³⁰ Korea Astronomy and Space Science Institute, Daejon 305-348, Korea
³¹ Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland New Zealand
³² Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
³³ Universidad de Concepción, Departamento de Física, Casilla 160-C, Concepción, Chile
³⁴ Institute ofAstronomy, University of Cambridge, Madingley Road, CB3 0 HA Cambridge, UK

Received: 8 March 2009
Accepted: 2 September 2010

Abstract

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.