The Evolutionary Timescale of Sakurai’s Object: A Test of Convection Theory?
The Evolutionary Timescale of Sakurai’s Object: A Test of Convection Theory?
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樱井天体的演化时间尺度：对流理论的检验？
DOI：
10.1086/320911
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
F. Herwig
中科院分区：
文献类型：
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作者：
F. Herwig
樱井的天体（人马座V4334）是一颗在非常晚的热脉冲之后又一次出现的渐近巨星分支星星。到目前为止，还没有恒星演化模型能够解释这颗星星的极快演化，这颗恒星在短短几年内就从白矮星之前的阶段变成了现在的巨星。一个非常高的恒星质量可以被排除作为快速演化的原因。相反，演化的时间尺度再现恒星模型的假设，元素混合在He闪光对流区在很晚的热脉冲的效率小于混合长度理论（MLT）的预测。因此，来自快速质子捕获的主要能量产生发生在更靠近表面的地方，并且膨胀到巨大状态的时间被加速到几年。假设V4334 Sgr的质量为0.604 M，这与4 kpc的距离一致，需要将MLT混合效率降低约100倍，以匹配其演变时间尺度。如果V4334 Sgr的质量较小，因此距离也较小，则此值会减小。然而，对于最小可能的质量，该效应并不消失。这些发现可能会提出一个半经验约束元素混合在对流区的恒星内部。
Sakurai's Object (V4334 Sagittarii) is a born-again asymptotic giant branch star following a very late thermal pulse. So far, no stellar evolution models have been able to explain the extremely fast evolution of this star, which has taken it from the pre-white dwarf stage to its current appearance as a giant within only a few years. A very high stellar mass can be ruled out as the cause of the fast evolution. Instead, the evolution timescale is reproduced in stellar models by making the assumption that the efficiency for element mixing in the He-flash convection zone during the very late thermal pulse is smaller than predicted by the mixing-length theory (MLT). As a result, the main energy generation from fast proton capture occurs closer to the surface, and the expansion to the giant state is accelerated to a few years. Assuming a mass of V4334 Sgr of 0.604 M☉—which is consistent with a distance of 4 kpc—a reduction of the MLT mixing efficiency by a factor of ~100 is required to match its evolutionary timescale. This value decreases if V4334 Sgr has a smaller mass and, accordingly, a smaller distance. However, the effect does not disappear for the smallest possible masses. These findings may present a semiempirical constraint on the element mixing in convective zones of the stellar interior.