Issue |
A&A
Volume 460, Number 1, December II 2006
|
|
---|---|---|
Page(s) | 277 - 288 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20054414 | |
Published online | 12 September 2006 |
OGLE 2004–BLG–254: a K3 III Galactic bulge giant spatially resolved by a single microlens
1
PLANET/Robonet Collaboration
2
Astronomisches Rechen-Institut (ARI), Zentrum für Astronomie der Universität Heidelberg (ZAH), MönchhofStr. 12-14, 69120 Heidelberg, Germany e-mail: cassan@ari.uni-heidelberg.de
3
Institut d'Astrophysique de Paris, UMR 7095 CNRS – Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
4
Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, Université Paul Sabatier – Toulouse 3, 14 avenue Edouard Belin, 31400 Toulouse, France
5
European Southern Observatory (ESO), Casilla 19001, Vitacura 19, Santiago, Chile
6
University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK
7
University of Tasmania, Physics Department, GPO 252C, Hobart, Tasmania 7001, Australia
8
Institute of Theoretical Physics, Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
9
Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
10
University of Canterbury, Department of Physics & Astronomy, Private Bag 4800, Christchurch, New Zealand
11
University of Notre Dame, Physics Department, 225 Nieuwland Science Hall, Notre Dame, IN 46530, USA
12
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
13
University of Texas, McDonald Observatory, Fort Davis TX 79734, USA
14
Dept Physics / Boyden Observatory, University of the Free State, Bloemfontein 9300, South Africa
15
Institute of Geophysics and Planetary Physics, L-413, Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94550, USA
16
DSM/DAPNIA, CEA Saclay, 91191 Gif-sur-Yvette cedex, France
17
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
18
Technical University of Vienna, Dept. of Computing, Wiedner Hauptstrasse 10, Vienna, Austria
19
Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055, USA
20
Perth Observatory, Walnut Road, Bickley, Perth 6076, Australia
21
South African Astronomical Observatory, PO Box 9 Observatory 7935, South Africa
22
OGLE Collaboration
23
Warsaw University Observatory. Al. Ujazdowskie 4, 00-478 Warszawa, Poland
24
Universidad de Concepción, Departamento de Física, Casilla 160-C, Concepción, Chile
25
Jodrell Bank Observatory, The University of Manchester, Macclesfield, Cheshire SK11 9DL, UK
Received:
25
October
2005
Accepted:
4
September
2006
Aims. We present an analysis of OGLE 2004–BLG–254, a
high-magnification () and relatively short
duration (
days) microlensing event in which the
source star, a Bulge K-giant, has been spatially resolved by a
point-like lens. We seek to determine the lens and source distance,
and provide a measurement of the linear limb-darkening coefficients of
the source star in the I and R bands. We discuss the derived values of the latter
and compare them to the classical theoretical
laws, and furthermore examine the cases of already published
microlensed GK-giants limb-darkening measurements.
Methods. We have obtained dense photometric coverage of the event light curve
with OGLE and PLANET telescopes, as well as a
high signal-to-noise ratio spectrum taken while the source
was still magnified by , using the UVES/VLT spectrograph.
We have performed a modelling of the light curve, including finite source
and parallax effects, and have combined spectroscopic and photometric
analysis to infer the source distance. A Galactic model for the mass and velocity
distribution of the stars has been used to estimate the lens distance.
Results. From the spectrum analysis and calibrated color-magnitude
of the event target, we found that the source was a K3 III Bulge giant,
situated at the far end of the Bulge.
From modelling the light curve, we have derived an angular size of
the Einstein ring as, and a relative
lens-source proper motion
mas/yr.
We could also measure the angular size of the source,
as,
whereas given the short duration of the event,
no significant constraint could be obtained from parallax
effects.
A Galactic model based on the modelling of the light curve
then provides us with an estimate of the lens distance, mass and velocity
as
kpc,
and
(at the lens distance) respectively.
Our dense coverage of this event allows us to measure limb darkening of the
source star in the I and R bands. We also compare previous measurements of linear
limb-darkening coefficients involving GK-giant stars with
predictions from ATLAS atmosphere models. We discuss the case of
K-giants and find a disagreement between limb-darkening
measurements and model predictions, which may be caused by
the inadequacy of the linear limb-darkening law.
Key words: gravitational lensing / techniques: high angular resolution / stars: atmospheres / stars: individual: OGLE 2004–BLG–254
© ESO, 2006
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