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首页> 外文期刊>The Astrophysical journal >EXPLORING THE UPPER RED GIANT AND ASYMPTOTIC GIANT BRANCHES: THE GLOBULAR CLUSTER M5
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EXPLORING THE UPPER RED GIANT AND ASYMPTOTIC GIANT BRANCHES: THE GLOBULAR CLUSTER M5

机译：探索上部红色巨型和渐近巨型分支：球形群集M5

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摘要

We have tabulated lists of upper red giant, horizontal-, and asymptotic giant branch (RGB, HB, and AGB) stars in the globular cluster M5 that are complete to over 10′ from the core for the RGB and AGB samples, and 8′ for the HB sample. The large samples give us the most precise value of R_2 = N_(AGB)/N_(HB) to date for a single globular cluster (0.176 +- 0.018). This is incompatible with theoretical calculations using the most recent physical inputs. The discrepancy can probably be attributed to the dependence of observed R_2 values on HB morphology. We identify the cluster M55 as another possible example of this effect. Samples of HB and AGB stars in populous clusters may provide a means of calibrating the masses of HB stars in globular clusters. The cumulative luminosity function of the upper RGB shows an apparent deficit of observed stars near the tip of the branch. This feature has less than a 2% chance of being due to statistical fluctuations. The slope of the cumulative luminosity function for AGB stars is consistent with the theoretically predicted value from stellar models when measurement bias is taken into account. We also introduce a new diagnostic R_(clump) that reflects the fraction of the AGB lifetime that a star spends in the AGB clump. For M5 we find R_(clump) = 0.42 +- 0.05, in marginal disagreement with theoretical predictions. Finally, we note that the blue half of M5's instability strip (where first-overtone RR Lyrae stars reside) is underpopulated, based on the large numbers of fundamental mode RR Lyrae stars and on the nonvariable stars at the blue end of the instability strip. This fact may imply that the evolutionary tracks (and particularly the colors) of stars in the instability strip are affected by pulsations.
机译：我们列出了球状星团M5中上部红色巨星，水平和渐近巨星（RGB，HB和AGB）星的列表，这些星离RGB和AGB样本距核心的距离超过10'，而8'用于HB样品。迄今为止，对于单个球状星团，大样本为我们提供了最精确的R_2 = N_（AGB）/ N_（HB）值（0.176 +-0.018）。这与使用最新物理输入的理论计算不兼容。差异可能归因于观察到的R_2值对HB形态的依赖性。我们将群集M55确定为这种效果的另一个可能示例。人口稠密星团中的HB和AGB恒星样本可以提供一种校准球状星团中HB恒星质量的方法。较高的RGB的累积光度函数显示在分支的尖端附近观察到的恒星明显不足。由于统计波动，此功能的可能性不到2％。当考虑到测量偏差时，AGB星的累积光度函数的斜率与恒星模型的理论预测值一致。我们还引入了一种新的诊断性R_（clump），它反映了恒星在AGB团块中度过的AGB寿命的一部分。对于M5，我们发现R_（clump）= 0.42 +-0.05，与理论预测略有不同。最后，我们注意到，M5不稳定带的蓝色一半（第一泛音RR Lyrae恒星所在的地方）的人口不足，这是基于大量基本模式RR Lyrae恒星和不稳定带蓝色端的不变星引起的。这个事实可能暗示不稳定带中恒星的演化轨迹（尤其是颜色）会受到脉动的影响。

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