TY  - JOUR
A1  - Cassan, A.
A1  - Beaulieu, Jean-Philippe
A1  - Brillant, Stephane
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Donatowicz, J.
A1  - Jorgensen, Uffe Grae
A1  - Kubas, Daniel
A1  - Albrow, Michael D.
A1  - Caldwell, John A. R.
A1  - Fouque, P.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Kane, Stephen R.
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, K. R.
A1  - Sahu, K. C.
A1  - Vinter, C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
A1  - Fendt, Christian
A1  - Hauschildt, P.
A1  - Heinmueller, Janine
A1  - Marquette, Jean-Baptiste
A1  - Thurl, C.
T1  - Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlensed H alpha line
N2  - We discuss high-resolution, time-resolved spectra of the caustic exit of the binary microlensing event OGLE 2002-BLG-069 obtained with UVES on the VLT. The source star is a G5III giant in the Galactic Bulge. During such events, the source star is highly magnified, and a strong differential magnification around the caustic resolves its surface. Using an appropriate model stellar atmosphere generated by the PHOENIX v2.6 code we obtain a model light curve for the caustic exit and compare it with a dense set of photometric observations obtained by the PLANET microlensing follow up network. We further compare predicted variations in the Halpha equivalent width with those measured from our spectra. While the model and observations agree in the gross features, there are discrepancies suggesting shortcomings in the model, particularly for the Halpha line core, where we have detected amplified emission from the stellar chromosphere after the source star's trailing limb exited the caustic. This achievement became possible by the provision of the very efficient OGLE-III Early Warning System, a network of small telescopes capable of nearly-continuous round-the-clock photometric monitoring, on-line data reduction, daily near-real-time modelling in order to predict caustic crossing parameters, and a fast and efficient response of a 8 m class telescope to a "Target-of-Opportunity" observation request
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Jiang, G. F.
A1  - DePoy, D. L.
A1  - Gal-Yam, A.
A1  - Gaudi, B. S.
A1  - Gould, A.
A1  - Han, C.
A1  - Lipkin, Y.
A1  - Maoz, D.
A1  - Ofek, E. O.
A1  - Park, B. G.
A1  - Pogge, R. W.
A1  - Udalski, A.
A1  - Kubiak, Marcin
A1  - Szymanski, M. K.
A1  - Szewczyk, O.
A1  - Zerbrun, K.
A1  - Wyrzykowski, L.
A1  - Soszynski, I.
A1  - Pietrzynski, G.
A1  - Albrow, Michael D.
A1  - Beaulieu, Jean-Philippe
A1  - Caldwell, John A. R.
A1  - Cassan, A.
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Donatowicz, J.
A1  - Fouque, P.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Jorgensen, S. F.
A1  - Jorgensen, Uffe Grae
A1  - Kane, Stephen R.
A1  - Kubas, Daniel
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, R.
A1  - Sahu, K. C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
T1  - OGLE-2003-BLG-238 : Microlensing mass estimate of an isolated star
N2  - Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M (c(2)/4G)(r) over tilde (E)theta(E) and so requires the measurement of both the angular Einstein radius theta(E) and the projected Einstein radius (r) over tilde (E). Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (I-min 10.3), high-magnification (A(max) 170) microlensing event. Pronounced finite-source effects permit a measurement of theta(E) = 650 muas. Although the timescale of the event is only t(E) 38 days, one can still obtain weak constraints on the microlens parallax: 4.4 AU < <(r)over tilde>(E) < 18 AU at the 1 &sigma; level. Together these two parameter measurements yield a range for the lens mass of 0.36 M-&ODOT; < M < 1.48 M-&ODOT;. As was the case for MACHO- LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements
Y1  - 2004
SN  - 0004-637X
ER  -