Department of Physics and Astronomy, National Institute of Technology, Rourkela 769008, Odisha, India
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Rabiańska 8, PL-87-100 Toruń, Poland
Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research (TIFR), Mumbai 400005, Maharashtra, India
Indian Institute of Astrophysics, Bangalore 560034, Karnataka, India
我们使用紫外成像望远镜 (UVIT) 的两个远紫外 (FUV: 1300 1800 Å) 和三个近紫外 (NUV: 2000 3000 Å) 滤光片获得的数据，展示了对银河球状星团 NGC 7492 的详细光度观测 -登上 AstroSat 卫星。我们使用 GAIA 数据版本 2（Gaia DR2）自行数据确认了提取源的集群成员资格。我们使用了使用 UVIT 和 GAIA 过滤器的颜色星等图 (CMD) 来区分星团中存在的恒星的不同演化阶段。我们已经使用紫外线和紫外线光学 CMD 在星团核心识别出一颗新的极端水平分支 (EHB) 恒星。通过用簇参数拟合 BaSTI 等时线获得的簇的估计距离模量为 16.95±0.05，[Fe/H] = -1.8 dex 和年龄 = 12.0 Gyr 在 V - I vs V CMD 上。有趣的是，在 UVIT 的 FUV 过滤器中仅检测到紫外线明亮热源中的 EHB 星和蓝色水平分支星（BHBs）。我们使用色温关系和多波段滤波器的光谱能量分布 (SED) 推导出了 BHB 的有效温度，其范围从 8,000 K 到 10,500 K。我们通过拟合巴斯蒂扎哈。对应于最佳拟合等时线的 BHB 的 He 丰度范围为 0.247 至 0.350。我们使用 SED 拟合和后 HB 进化轨迹估计了星团中新发现的 EHB 恒星的各种物理参数。我们研究了在 UVIT 中检测到的所有簇源的径向分布。在 FUV 过滤器中检测到的光源超出了星团的半光半径 (1.15')，
We present detailed photometric observations of the Galactic globular cluster NGC 7492 using the data obtained with two far-ultraviolet (FUV: 1300 1800 Å) and three near-ultraviolet (NUV: 2000 3000 Å) filters of Ultraviolet Imaging Telescope (UVIT) on-board the AstroSat satellite. We confirmed the cluster membership of the extracted sources using GAIA data release 2 (Gaia DR2) proper motion data. We have used color-magnitude diagrams (CMDs) using UVIT and GAIA filters to separate out different evolutionary stages of the stars present in the cluster. We have identified a new extreme horizontal branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The estimated distance-modulus of the cluster is 16.95±0.05 obtained by fitting BaSTI isochrones with cluster parameters, [Fe/H] = −1.8 dex and age = 12.0 Gyr on the V − I vs V CMD. Interestingly, only the EHB star and blue horizontal branch stars (BHBs) among the UV-bright hot sources are detected in FUV filters of UVIT. We have derived the effective temperature of BHBs using color-temperature relation and spectral energy distributions (SEDs) of multi-band filters, which are in the range from 8,000 K to 10,500 K. We find a variation of He abundance of BHBs by fitting the BaSTI ZAHB. The range in the He abundance of the BHBs corresponding to the best fit isochrones is 0.247 to 0.350. We have estimated various physical parameters of the newly identified EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have studied the radial distribution of all the sources of the cluster detected in UVIT. The sources detected in FUV filters extend beyond the half light radius (1.15′) of the cluster, whereas the sources detected in NUV filters extend beyond the tidal radius (9.2′) of the cluster.
