OGLE 2008-BLG-290: an accurate measurement of the limb darkening of a galactic bulge K Giant spatially resolved by microlensing

July 2010 • 2010A&A...518A..51F

Authors • Fouqué, P. • Heyrovský, D. • Dong, S. • Gould, A. • Udalski, A. • Albrow, M. D. • Batista, V. • Beaulieu, J. -P. • Bennett, D. P. • Bond, I. A. • Bramich, D. M. • Calchi Novati, S. • Cassan, A. • Coutures, C. • Dieters, S. • Dominik, M. • Dominis Prester, D. • Greenhill, J. • Horne, K. • Jørgensen, U. G. • Kozłowski, S. • Kubas, D. • Lee, C. -H. • Marquette, J. -B. • Mathiasen, M. • Menzies, J. • Monard, L. A. G. • Nishiyama, S. • Papadakis, I. • Street, R. • Sumi, T. • Williams, A. • Yee, J. C. • Brillant, S. • Caldwell, J. A. R. • Cole, A. • Cook, K. H. • Donatowicz, J. • Kains, N. • Kane, S. R. • Martin, R. • Pollard, K. R. • Sahu, K. C. • Tsapras, Y. • Wambsganss, J. • Depoy, D. L. • Gaudi, B. S. • Han, C. • Lee, C. -U. • Park, B. -G. • Kubiak, M. • Szymański, M. K. • Pietrzyński, G. • Soszyński, I. • Szewczyk, O. • Ulaczyk, K. • Abe, F. • Fukui, A. • Furusawa, K. • Gilmore, A. C. • Hearnshaw, J. B. • Itow, Y. • Kamiya, K. • Kilmartin, P. M. • Korpela, A. V. • Lin, W. • Ling, C. H. • Masuda, K. • Matsubara, Y. • Miyake, N. • Muraki, Y. • Nagaya, M. • Ohnishi, K. • Okumura, T. • Perrott, Y. • Rattenbury, N. J. • Saito, To. • Sako, T. • Sato, S. • Skuljan, L. • Sullivan, D. • Sweatman, W. • Tristram, P. J. • Allan, A. • Bode, M. F. • Burgdorf, M. J. • Clay, N. • Fraser, S. N. • Hawkins, E. • Kerins, E. • Lister, T. A. • Mottram, C. J. • Saunders, E. S. • Snodgrass, C. • Steele, I. A. • Anguita, T. • Bozza, V. • Harpsøe, K. • Hinse, T. C. • Hundertmark, M. • Kjærgaard, P. • Liebig, C. • Mancini, L. • Masi, G. • Rahvar, S. • Ricci, D. • Scarpetta, G. • Southworth, J. • Surdej, J. • Thöne, C. C. • Riffeser, A. • Seitz, S.

Abstract • Context. Not only is gravitational microlensing a successful tool for discovering distant exoplanets, but it also enables characterization of the lens and source stars involved in the lensing event.
Aims: In high-magnification events, the lens caustic may cross over the source disk, which allows determination of the angular size of the source and measurement of its limb darkening.
Methods: When such extended-source effects appear close to maximum magnification, the resulting light curve differs from the characteristic Paczyński point-source curve. The exact shape of the light curve close to the peak depends on the limb darkening of the source. Dense photometric coverage permits measurement of the respective limb-darkening coefficients.
Results: In the case of the microlensing event OGLE 2008-BLG-290, the K giant source star reached a peak magnification at about 100. Thirteen different telescopes have covered this event in eight different photometric bands. Subsequent light-curve analysis yielded measurements of linear limb-darkening coefficients of the source in six photometric bands. The best-measured coefficients lead to an estimate of the source effective temperature of about 4700⁺¹⁰⁰_-200 K. However, the photometric estimate from colour-magnitude diagrams favours a cooler temperature of 4200 ± 100 K.
Conclusions: Because the limb-darkening measurements, at least in the CTIO/SMARTS2 V_s- and I_s-bands, are among the most accurate obtained, the above disagreement needs to be understood. A solution is proposed, which may apply to previous events where such a discrepancy also appeared.

Links

• PREPRINT http://arxiv.org/abs/1005.0966
• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/201014053/postscript
• ELECTR https://doi.org/10.1051%2F0004-6361%2F201014053
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2010A%26A...518A..51F
• PDF https://www.aanda.org/10.1051/0004-6361/201014053/pdf
• DATA https://irsa.ipac.caltech.edu/bibdata/2010/F/2010A&A...518A..51F.html