Naslov
OGLE 2004-BLG-254: a K3 III Galactic bulge giant spatially resolved by a single microlens

Autori
Cassan, A. ; Beaulieu, J.-P. ; Fouqué, P. ; Brillant, S. ; Dominik, M. ; Greenhill, J. ; Heyrovský, D. ; Horne, K. ; Jørgensen, U. G. ; Kubas, D. ; Stempels, H. C. ; Vinter, C. ; Albrow, M. D. ; Bennett, D. ; Caldwell, J. A. R. ; Calitz, J. J. ; Cook, K. ; Coutures, C. ; Dominis, Dijana ; Donatowicz, J. ; Hill, K. ; Hoffman, M. ; Kane, S. ; Marquette, J.-B. ; Martin, R. ; Meintjes, P. ; Menzies, J. ; Miller, V. R. ; Pollard, K. R. ; Sahu, K. C. ; Wambsganss, J. ; Williams, A. ; Udalski, A. ; Szymański, M. K. ; Kubiak, M. ; Pietrzyński, G. ; Soszyński, I. ; Żebruń, K. ; Szewczyk, O. ; Wyrzykowski, Ł.

Izvornik
Astronomy and Astrophysics (0004-6361) 460 (2006), 1; 277-288

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
gravitational lensing; techniques: high angular resolution; stars: atmospheres; stars:; individual: OGLE 2004-BLG-254

Sažetak
We present an analysis of OGLE 2004-BLG-254, a high-magnification (Â &simeq ; 60) and relatively short duration (t_E&simeq ; 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&simeq ; 114 μ as, and a relative lens-source proper motion μ = θ _E/t_E&simeq ; 3.1 mas/yr. We could also measure the angular size of the source, θ _*&simeq ; 4.5 μ 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 D_L&simeq ; 9.6 kpc, M&simeq ; 0.11 Mȯ and v &simeq ; 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.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA