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OGLE 2004-BLG-254: a K3III Galactic bulge giant spatially resolved by a single microlens

Citation

Cassan, A and Beaulieu, JP and Fouque, P and Brilliant, S and Dominik, M and Greenhill, JG and Heyrovsky, D and Horne, K and Jorgensen, UG and Kubas, D and Stempels, HC and Vinter, C and Albrow, MD and Bennett, D and Caldwell, JAR and Calitz, JJ and Cook, K and Coutures, C and Dominis, D and Donatowicz, J and Hill, KM and Hoffman, M and Kane, S and Marquette, JB and Martin, R and Meintjes, P and Menzies, J and Miller, VR and Pollard, K and Sahu, K and Wambsganss, J and Williams, A and Udalski, A and Szymanski, MK and Kubiak, M and Pietrzynski, G and Soszynski, I and Zebrun, K and Szewczyk, O and Wyrzykowski, L, OGLE 2004-BLG-254: a K3III Galactic bulge giant spatially resolved by a single microlens, Astronomy & Astrophysics , 460, (1) pp. 277-288. ISSN 0004-6361 (2006) [Refereed Article]

DOI: doi:10.1051/0004-6361:20054414

Abstract

Aims. We present an analysis of OGLE 2004-BLG-254, a high-magnification (A o ≃ 60) and relatively short duration (A o ≃ 13.2 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 A ∼ 20, 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 θ E ≃ 114 μas, and a relative lens-source proper motion μ = θ E/t E ≃ 3.1 mas/yr. We could also measure the angular size of the source, θ*, ≃ 4.5 μas, 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 D L ≃ 9.6 kpc, M ≃ 0.11 M ⊙ and v ≃ 145 km s -1 (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. © ESO 2006.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Galactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Greenhill, JG (Dr John Greenhill)
Author:Hill, KM (Dr Kym Hill)
ID Code:41301
Year Published:2006
Web of Science® Times Cited:19
Deposited By:Physics
Deposited On:2006-08-01
Last Modified:2011-09-21
Downloads:0

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