The evolution of a rapidly accreting helium white dwarf to become a low-luminosity helium star
The evolution of a rapidly accreting helium white dwarf to become a low-luminosity helium star
复制标题
DOI：
10.1046/j.1365-8711.2000.03221.x
复制
发表时间：
2000-04
影响因子：
4.8
通讯作者：
H. Saio;C. Jeffery
中科院分区：
文献类型：
--
作者：
H. Saio;C. Jeffery
我们研究了合并后的低质量双白色矮星演化为低光度（或高重力）的极端氦星。我们已经通过物质的快速吸积来近似合并过程，主要由氦组成，到氦白色矮星上。积累到一定质量后，氦壳闪光发生，半径和光度增加，星星变成黄巨星。当总质量达到预定值时，人工停止质量吸积。当燃烧氦的壳层随着重复的壳层闪光向内移动时，有效温度随着星星向氦主序星演化而逐渐升高。当燃烧氦的壳层内部的质量约为0.25 M质量时，星星进入一个脉动不稳定的状态。我们得到了这些模型的径向脉动周期。这些模型的性质与脉动氦星星V652 Her的性质非常相似，我们将理论模型的周期变化率与V652 Her的观测值以及它在Hertzsprung-Russell图上的位置进行了比较。我们的结论是，两个氦白色矮星之间的合并可以产生一个星星的性质非常相似，在至少一个极端的氦星星中观察到的，是一个可行的模型，为他们的进化起源。这样的氦星会演化成靠近氦主序星的热次矮星。我们还讨论了低光度氦星的数量在银河系中预期我们的演化方案。
We have examined the evolution of merged low-mass double white dwarfs which become low-luminosity (or high-gravity) extreme helium stars. We have approximated the merging process by the rapid accretion of matter, consisting mostly of helium, on to a helium white dwarf. After a certain mass is accumulated, a helium shell flash occurs, the radius and luminosity increase and the star becomes a yellow giant. Mass accretion is stopped artificially when the total mass reaches a pre-determined value. As the helium-burning shell moves inwards with repeating shell flashes, the effective temperature gradually increases as the star evolves towards the helium main sequence. When the mass interior to the helium-burning shell is approximately 0.25 M⊙, the star enters a regime where it is pulsationally unstable. We have obtained radial pulsation periods for these models. These models have properties very similar to those of the pulsating helium star V652 Her. We have compared the rate of period change of the theoretical models with that observed in V652 Her, as well as with its position on the Hertzsprung–Russell diagram. We conclude that the merger between two helium white dwarfs can produce a star with properties remarkably similar to those observed in at least one extreme helium star, and is a viable model for their evolutionary origin. Such helium stars will evolve to become hot subdwarfs close to the helium main sequence. We also discuss the number of low-luminosity helium stars in the Galaxy expected for our evolution scenario.