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UVIT study of UV bright stars in the globular cluster NGC 4147
Journal of Astrophysics and Astronomy ( IF 1.1 ) Pub Date : 2021-06-09 , DOI: 10.1007/s12036-020-09687-y
Ranjan Kumar , Ananta C. Pradhan , Mudumba Parthasarathy , Devendra K. Ojha , Abhisek Mohapatra , Jayant Murthy , Santi Cassisi

We present far ultraviolet (FUV) observations of globular cluster NGC 4147 using three FUV filters, BaF\(_2\) (F154W), sapphire (F169M), and silica (F172M) of Ultra-Violet Imaging Telescope (UVIT) on-board the AstroSat satellite. We confirmed the cluster membership of the UVIT observed sources using proper motions from Gaia data release 2 (GAIA DR2). We identified 37 blue horizontal branch stars (BHBs), one blue straggler star (BSS) and 15 variable stars using UV-optical color magnitude diagrams (CMDs). We find that all the FUV bright BHBs are second generation population stars. Using UV-optical CMDs, we identify two sub-populations, BHB1 and BHB2, among the UV-bright BHBs in the cluster with stars count ratio of 24:13 for BHB1 and BHB2. The effective temperatures (\(T_{\mathrm {eff}}\)) of BHB1 and BHB2 were derived using color-temperature relation of BaSTI-IAC zero-age horizontal branch (ZAHB). We found that BHB1 stars are more centrally concentrated than BHB2 stars. We also derive physical parameters of the detected FUV bright BSS by fitting younger age BaSTI-IAC isochrones on optical and UV-optical CMDs.



中文翻译:

球状星团 NGC 4147 中紫外亮星的 UVIT 研究

我们使用三种 FUV 滤光片、BaF \(_2\) (F154W)、蓝宝石 (F169M) 和机载紫外成像望远镜 (UVIT) 的二氧化硅 (F172M)呈现球状星团 NGC 4147 的远紫外 (FUV) 观测AstroSat 卫星。我们使用来自 Gaia 数据发布 2 (GAIA DR2) 的适当运动确认了 UVIT 观测源的集群成员。我们使用紫外光学彩色星等图 (CMD) 确定了 37 颗蓝色水平分支星 (BHB)、1 颗蓝色落后星 (BSS) 和 15 颗变星。我们发现所有的 FUV 明亮 BHB 都是第二代人口星。使用紫外光 CMD,我们在星团中的紫外光 BHB 中识别出两个亚群 BHB1 和 BHB2,BHB1 和 BHB2 的恒星计数比为 24:13。有效温度 ( \(T_{\mathrm {eff}}\)) 的 BHB1 和 BHB2 是使用 BaSTI-IAC 零龄水平分支 (ZAHB) 的色温关系得出的。我们发现 BHB1 恒星比 BHB2 恒星更集中。我们还通过在光学和紫外光学 CMD 上拟合年轻的 BaSTI-IAC 等时线来推导出检测到的 FUV 明亮 BSS 的物理参数。

更新日期:2021-06-09
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