AGE AND STRUCTURE PARAMETERS OF THE REMOTE M31 GLOBULAR CLUSTER B514 BASED ON HST, 2MASS, GALEX, AND BATC OBSERVATIONS
AGE AND STRUCTURE PARAMETERS OF THE REMOTE M31 GLOBULAR CLUSTER B514 BASED ON HST, 2MASS, GALEX, AND BATC OBSERVATIONS
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DOI：
10.1088/0004-6256/143/2/29
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发表时间：
2011-11
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通讯作者：
Jun Ma;Song-Yun Wang;Zhenyu Wu;Z. Fan;Tianmeng Zhang;Jianghua Wu;Xu Zhou;Zhao-ji Jiang;Jian-sheng Chen
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作者：
Jun Ma;Song-Yun Wang;Zhenyu Wu;Z. Fan;Tianmeng Zhang;Jianghua Wu;Xu Zhou;Zhao-ji Jiang;Jian-sheng Chen
B514是一个遥远的M31球状星团（GC），其投影距离为Rp≃55 kpc。利用哈勃太空望远镜上的先进巡天相机进行深度观测，精确地提供了B514的综合光和恒星数量。通过对集成光的分布与恒星数的耦合分析，我们能够可靠地跟踪到~ 40″的星团轮廓。在此基础上，详细研究了其在F606W和F814W滤波器中的表面亮度分布，并通过拟合单质量各向同性King模型确定了其结构参数。结果表明，r bbb10″的表面亮度分布偏离了最适合的King模型。B514的内部区域相当平坦，比大多数相同光度的普通gc有更大的半光半径。有趣的是，在MV相对于log Rh平面上，B514几乎位于Mackey & van den Bergh定义的普通gc的阈值上。此外，B514作为北京-亚利桑那-台湾-康涅狄格洲（BATC）多色巡天计划的一部分被观测到，使用13个中波段滤光片覆盖3000-8500波长范围Å。基于孔径光度法，我们得到了13个BATC滤波器定义的光谱能量分布（SEDs）。我们通过比较它的SEDs（从2267到20000 Å，由星系演化探测器的近紫外波段、5个斯隆数字巡天波段、13个BATC中波段滤光片和2个微米巡天近红外jhk滤光片组成）和理论恒星群合成模型来确定星团的年龄和质量，结果得出它的年龄为11.5±3.5 Gyr。这个年龄证实了之前的建议，即B514是M31中的一个老GC。B514的质量为0.96-1.08 × 106 M☉，是M31中一颗中等质量的GC。
B514 is a remote M31 globular cluster (GC) which is located at a projected distance of Rp ≃ 55 kpc. Deep observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate integrated light and star counts of B514. By coupling the analysis of the distribution of the integrated light with star counts, we are able to reliably follow the profile of the cluster out to ∼40″. Based on the combined profile, we study in detail its surface brightness distribution in the F606W and F814W filters and determine its structural parameters by fitting a single-mass isotropic King model. The results showed that the surface brightness distribution departs from the best-fit King model for r > 10″. B514 is quite flat in the inner region and has a larger half-light radius than the majority of normal GCs of the same luminosity. It is interesting that, in the MV versus log Rh plane, B514 lies nearly on the threshold for ordinary GCs as defined by Mackey & van den Bergh. In addition, B514 was observed as part of the Beijing–Arizona–Taiwan–Connecticut (BATC) Multicolor Sky Survey, using 13 intermediate-band filters covering a wavelength range of 3000–8500 Å. Based on aperture photometry, we obtain its spectral energy distributions (SEDs) as defined by the 13 BATC filters. We determine the cluster's age and mass by comparing its SEDs (from 2267 to 20000 Å, comprised of photometric data from the near-ultraviolet band of the Galaxy Evolution Explorer, 5 Sloan Digital Sky Survey bands, 13 BATC intermediate-band filters, and Two Micron All Sky Survey near-infrared JHKs filters) with theoretical stellar population synthesis models, resulting in an age of 11.5 ± 3.5 Gyr. This age confirms the previous suggestion that B514 is an old GC in M31. B514 has a mass of 0.96–1.08 × 106 M☉ and is a medium-mass GC in M31.