July
2010
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2010A&A...518A..51F
Authors
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Fouqué, P.
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Heyrovský, D.
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Dong, S.
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Gould, A.
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Udalski, A.
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Albrow, M. D.
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Batista, V.
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Beaulieu, J. -P.
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Bennett, D. P.
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Bond, I. A.
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Bramich, D. M.
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Calchi Novati, S.
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Cassan, A.
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Coutures, C.
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Dieters, S.
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Dominik, M.
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Dominis Prester, D.
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Greenhill, J.
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Horne, K.
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Jørgensen, U. G.
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Kozłowski, S.
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Kubas, D.
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Lee, C. -H.
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Marquette, J. -B.
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Mathiasen, M.
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Menzies, J.
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Monard, L. A. G.
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Nishiyama, S.
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Papadakis, I.
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Street, R.
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Sumi, T.
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Williams, A.
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Yee, J. C.
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Brillant, S.
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Caldwell, J. A. R.
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Cole, A.
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Cook, K. H.
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Donatowicz, J.
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Kains, N.
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Kane, S. R.
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Martin, R.
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Pollard, K. R.
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Sahu, K. C.
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Tsapras, Y.
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Wambsganss, J.
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Depoy, D. L.
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Gaudi, B. S.
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Han, C.
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Lee, C. -U.
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Park, B. -G.
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Kubiak, M.
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Szymański, M. K.
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Pietrzyński, G.
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Soszyński, I.
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Szewczyk, O.
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Ulaczyk, K.
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Abe, F.
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Fukui, A.
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Furusawa, K.
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Gilmore, A. C.
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Hearnshaw, J. B.
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Itow, Y.
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Kamiya, K.
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Kilmartin, P. M.
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Korpela, A. V.
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Lin, W.
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Ling, C. H.
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Masuda, K.
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Matsubara, Y.
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Miyake, N.
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Muraki, Y.
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Nagaya, M.
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Ohnishi, K.
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Okumura, T.
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Perrott, Y.
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Rattenbury, N. J.
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Saito, To.
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Sako, T.
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Sato, S.
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Skuljan, L.
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Sullivan, D.
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Sweatman, W.
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Tristram, P. J.
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Allan, A.
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Bode, M. F.
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Burgdorf, M. J.
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Clay, N.
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Fraser, S. N.
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Hawkins, E.
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Kerins, E.
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Lister, T. A.
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Mottram, C. J.
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Saunders, E. S.
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Snodgrass, C.
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Steele, I. A.
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Anguita, T.
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Bozza, V.
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Harpsøe, K.
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Hinse, T. C.
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Hundertmark, M.
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Kjærgaard, P.
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Liebig, C.
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Mancini, L.
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Masi, G.
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Rahvar, S.
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Ricci, D.
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Scarpetta, G.
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Southworth, J.
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Surdej, J.
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Thöne, C. C.
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Riffeser, A.
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Seitz, S.
Abstract
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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.
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