标题： UOCS。 V. 使用AstroSat对旧的开放星团NGC 188的紫外研究 显示英文标题

标题： UOCS. V. UV study of the old open cluster NGC 188 using AstroSat

摘要： 我们展示了利用ASTROSAT卫星上的紫外成像望远镜（UVIT）获取的图像对古老疏散星团NGC188的紫外光度测量结果，在两个远紫外（FUV）和一个近紫外（NUV）滤光片下获得。 UVIT数据与光学光度数据结合，用于构建光学和紫外颜色-星等图（CMDs）。 在FUV图像中，我们仅检测到热且明亮的蓝离散星（BSSs）、一颗热亚矮星和一个白矮星（WD）候选者。 在NUV图像中，我们检测到亮度极限约为22星等的成员星，包括21个BSSs、2颗黄色离散星（YSSs）和一个WD候选者。 本研究首次呈现了NUV-光学CMDs，并叠加了更新的BaSTI-IAC等时线和WD冷却序列，这些模型与观测到的CMDs拟合良好。 我们使用光谱能量分布（SED）拟合来估计紫外明亮恒星的有效温度、半径和光度。 我们发现该星团具有包含三颗恒星的水平分支（HB）种群（Teff = 4750 - 21000 K）。 我们还检测到两颗黄色离散星，其中一颗与其双星性质和X射线辐射相关的紫外过量。 显示英文摘要

摘要： We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the ASTROSAT satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue straggler stars (BSSs), one hot subdwarf, and one white dwarf (WD) candidate. In the NUV images, we detect members up to a faintness limit of ~22 mag including 21 BSSs, 2 yellow straggler stars (YSSs), and one WD candidate. This study presents the first NUV-optical CMDs, and are overlaid with updated BaSTI-IAC isochrones and WD cooling sequence, which are found to fit well to the observed CMDs. We use spectral energy distribution (SED) fitting to estimate the effective temperatures, radii, and luminosities of the UV-bright stars. We find the cluster to have an HB population with three stars (Teff = 4750 - 21000 K). We also detect two yellow straggler stars, with one of them with UV excess connected to its binarity and X-ray emission.