OGLE 2004–BLG–254: a K3 III Galactic bulge giant spatially resolved by a single microlens
OGLE 2004–BLG–254: a K3 III Galactic bulge giant spatially resolved by a single microlens
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OGLE 2004–BLG–254：由单个微透镜空间解析的 K3 III 银河核球巨星
DOI：
10.1051/0004-6361:20054414
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发表时间：
2006
影响因子：
6.5
通讯作者：
L. Wyrzykowski
中科院分区：
文献类型：
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作者：
A. Cassan;J. Beaulieu;P. Fouqué;S. Brillant;M. Dominik;J. Greenhill;D. Heyrovský;K. Horne;U. Jørgensen;D. Kubas;H. C. Stempels;C. Vinter;M. Albrow;D. Bennett;J. Caldwell;J. Calitz;K. Cook;C. Coutures;D. Dominis;J. Donatowicz;K. Hill;M. Hoffman;S. Kane;J. Marquette;R. Martin;P. Meintjes;J. Menzies;V. R. Miller;K. Pollard;K. Sahu;J. Wambsganss;A. Williams;A. Udalski;M. Szymański;M. Kubiak;G. Pietrzyński;I. Soszyński;K. Żebruń;O. Szewczyk;L. Wyrzykowski
目标。我们提出了OGLE 2004-BLG-254，一个高放大倍数（A？? 60)和相对较短的持续时间（t_E？13.2天）的微透镜事件，其中的源星星，一个膨胀的K-巨星，已空间分辨的点状透镜。我们试图确定的透镜和源的距离，并提供了一个测量的线性边缘暗化系数的源星星在I和R波段。我们讨论了后者的衍生值，并将其与经典理论定律进行比较，并进一步研究了已经发表的微透镜GK-巨星边缘变暗测量的情况。方法：我们已经获得了密集的光度覆盖的事件光变曲线与OGLE和行星望远镜，以及高信噪比的光谱，而源仍然放大A？20，使用UVES/VLT光谱仪。我们已经进行了建模的光变曲线，包括有限的源和视差效应，并结合光谱和光度分析来推断源的距离。恒星质量和速度分布的银河系模型已被用来估计透镜距离。结果：通过光谱分析和标度的色星等，我们发现源是一颗K3 III膨胀巨星，位于膨胀的远端。从光变曲线的模型中，我们导出了爱因斯坦环的角尺寸。E？114？以及相对透镜源自行？= ?_ E/t_E？3.1质量/年我们也可以测量源的角大小，？4.5 ?由于事件持续时间较短，因此无法从视差效应中获得明显的限制。一个银河系模型的基础上建模的光变曲线，然后为我们提供了一个估计的透镜的距离，质量和速度为D_L？9.6科索沃保护团，M？0.11米吗？而V？145~km s-1（在透镜距离）。我们对这一事件的密集覆盖使我们能够在I和R波段测量源星星的临边变暗。我们还比较了以前的测量的线性边缘变暗系数涉及GK巨星与ATLAS大气模型的预测。我们讨论的情况下，K-巨星，并发现之间的不一致的边缘变暗的测量和模型的预测，这可能是由于线性边缘变暗的法律的不足。
Aims. We present an analysis of OGLE 2004-BLG-254, a high-magnification (A? ? 60) and relatively short duration (t_E? 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 ?_E? 114 ?as, and a relative lens-source proper motion ? = ?_E/t_E? 3.1 mas/yr. We could also measure the angular size of the source, ?_*? 4.5 ?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? 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.