M31中明亮年轻星系团的HST/WFPC巡天。II。低亮度团簇的野外测光
An HST/WFPC Survey of Bright Young Clusters in M31. II. Photometry of Less Luminous Clusters in the Fields
摘要：
本文报道了位于M31星盘中明亮的年轻星团（蓝色球状星团）附近的89个低质量星团的性质。其中82个簇是新检测到的。我们已经确定了它们的综合星等和颜色，基于一系列哈勃空间望远镜宽视场/行星相机2的蓝色和红色曝光（HST滤波器F450 W和F814 W）。综合视星等的范围从F450 W = 17.5到22.5，颜色显示了广泛的年龄范围。所有星团的恒星颜色星等图都被获得，那些有足够明亮恒星的星团被拟合到理论等时线，以提供年龄估计。年龄从1200万年到> 50000万年不等。红化，其平均E（F450 - F814）= 0.59，离散度为0.21等，是从这些星系团的主序列拟合得出的。这些年龄和综合颜色与太阳丰度的单种群理论模型的比较表明，在测试的年龄的颜色偏移0.085等。其余集群的估计年龄是基于它们的测量颜色。年龄-频率图显示，随着年龄的增长，数量急剧下降，在检测到的最年轻和最古老的集群之间的每个年龄间隔的数量大幅减少。
英文摘要：
We report on the properties of 89 low mass star clusters located in the vicinity of luminous young clusters (blue globulars) in the disk of M31. 82 of the clusters are newly detected. We have determined their integrated magnitudes and colors, based on a series of Hubble Space Telescope Wide Field/Planetary Camera 2 exposures in blue and red (HST filters F450W and F814W). The integrated apparent magnitudes range from F450W = 17.5 to 22.5, and the colors indicate a wide range of ages. Stellar color-magnitude diagrams for all clusters were obtained and those with bright enough stars were fit to theoretical isochrones to provide age estimates. The ages range from 12 Myr to >500 Myr. Reddenings, which average E(F450 - F814) = 0.59 with a dispersion of 0.21 magnitudes, were derived from the main sequence fitting for those clusters. Comparison of these ages and integrated colors with single population theoretical models with solar abundances suggests a color offset of 0.085 magnitudes at the ages tested. Estimated ages for the remaining clusters are based on their measured colors. The age-frequency diagram shows a steep decline of number with age, with a large decrease in number per age interval between the youngest and the oldest clusters detected.
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