论文标题
NGC 6752 -IV上的HST大型计划。白矮人序列
The HST large programme on NGC 6752 -- IV. The White Dwarf Sequence
论文作者
论文摘要
我们介绍了在球状群集NGC 6752中对白矮人冷却序列（WD CS）的最终研究。研究是专用哈勃太空望远镜大型程序的主要目标，现在为此收集了所有观察结果。 WD CS光度函数（LF）在M_F606W = 29.3 +/- 0.1处确认为峰值，在不确定性与先前报告的不确定性中保持一致，现在已完成至M_F606W〜29.7。我们已经与模型预测进行了鲁棒性和结论性的比较，这些预测表明了氢包膜WD模型的理论LF如何紧密遵循经验LF的形状。观察到的LF峰的大小与12.7至13.5 GYR之间的年龄相匹配，这与从主序列关闭的群集年龄相一致。我们还发现，群集中多个种群对WD LF的影响低于27.3的M_F606W是可以忽略的，并且存在很小一部分的氦信封对象与数据一致。我们的分析表明，在幅度范围28.1 <m_f606w <28.9的幅度范围内低估了模型的冷却时间尺度的可能提示。最后，我们发现，在中等和强退化性之间的跃迁中，通过电子传导不透明度计算出的氢包络模型提供了与主序列转盘年龄相比太小的WD年龄。
We present our final study of the white dwarf cooling sequence (WD CS) in the globular cluster NGC 6752. The investigation is the main goal of a dedicated Hubble Space Telescope large Program, for which all the observations are now collected. The WD CS luminosity function (LF) is confirmed to peak at m_F606W = 29.3+/-0.1, consistent within uncertainties with what has been previously reported, and is now complete down to m_F606W~29.7. We have performed robust and conclusive comparisons with model predictions that show how the theoretical LF for hydrogen envelope WD models closely follow the shape of the empirical LF. The magnitude of the peak of the observed LF is matched with ages between 12.7 and 13.5 Gyr, consistent with the cluster age derived from the main sequence turn off and subgiant branch. We also find that the impact of multiple populations within the cluster on the WD LF for m_F606W below 27.3 is negligible, and that the presence of a small fraction of helium envelope objects is consistent with the data. Our analysis reveals a possible hint of an underestimate of the cooling timescales of models in the magnitude range 28.1 < m_F606W < 28.9. Finally, we find that hydrogen envelope models calculated with a new tabulation of electron conduction opacities in the transition between moderate and strong degeneracy provide WD ages that are too small in comparison to the Main Sequence turnoff age.
