M13中稳定氢燃烧缓慢冷却的白矮星
Slowly cooling white dwarfs in M13 from stable hydrogen burning
摘要：
白矮星（WD）是宇宙中绝大多数恒星演化的最终产物。它们是电子简并结构，没有稳定的热核活动，它们的演化通常被描述为一个纯粹的冷却过程。它们的冷却速率被用来作为宇宙计时器来限制银河系中几个种群的年龄，包括盘状星团、球状星团和疏散星团。通过分析两个孪生星系球状星团（M3和M13）的高分辨率测光数据，我们发现M13中明亮的WD异常丰富。理论模型表明，与水平分支形态一致，这种过剩是由于M13中约70%的WD的冷却过程减慢，这是由其剩余富氢外壳中的稳定热核燃烧引起的。这是第一个静态热核活动发生在冷却WD的观测证据，它带来了新的关注使用WD冷却速率作为宇宙计时器的低金属环境。
英文摘要：
White Dwarfs (WDs) are the final evolutionary product of the vast majority of stars in the Universe. They are electron-degenerate structures characterized by no stable thermonuclear activity, and their evolution is generally described as a pure cooling process. Their cooling rate is adopted as cosmic chronometer to constrain the age of several Galactic populations, including the disk, globular and open clusters. By analysing high-resolution photometric data of two twin Galactic globular clusters (M3 and M13), we find a clear-cut and unexpected over-abundance of bright WDs in M13. Theoretical models suggest that, consistently with the horizontal branch morphology, this over-abundance is due to a slowing down of the cooling process in ~70% of the WDs in M13, caused by stable thermonuclear burning in their residual hydrogen-rich envelope. This is the first observational evidence of quiescent thermonuclear activity occurring in cooling WDs and it brings new attention on the use of the WD cooling rate as cosmic chronometer for low metallicity environments.
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