arXiv 2402.034902024-02-05astro-ph.SR

核心氦燃烧期间呼吸脉冲对富氢大气白矮星核心化学结构和脉动的影响

The impact of breathing pulses during core-helium burning on the core chemical structure and pulsations of hydrogen-rich atmosphere white dwarfs

Alejandro H. Córsico, Leandro G. Althaus

备注：: 9 pages, 1 table, 7 figures. Accepted for publication in The Astrophysical Journal

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AI总结：

本研究通过恒星演化模型，探讨核心氦燃烧阶段呼吸脉冲对白矮星核心化学结构和ZZ Ceti星脉动的影响，发现呼吸脉冲使核心更大、氧丰度更高，但不足以解释星震学观测，脉动周期差异可达约30秒。

摘要：

呼吸脉冲是在低质量和中等质量恒星的核心氦燃烧阶段可能发生的混合事件。呼吸脉冲的发生预计会对白矮星的形成和演化产生影响，特别是对其核心化学结构产生影响，而核心化学结构可以通过星震学进行探测。我们旨在探索呼吸脉冲对具有富氢包层的变白矮星（即ZZ Ceti星）的化学剖面和脉动特性的影响。我们计算了零年龄主序上质量为$1.0 M_{\odot}$和$2.5 M_{\odot}$的恒星模型，并将它们从核心氦燃烧阶段演化到渐近巨星支上的热脉冲阶段，最后演化到白矮星冷却的晚期阶段。我们比较了其前身星在核心氦燃烧阶段经历过呼吸脉冲的白矮星核心的化学结构，与未发生呼吸脉冲的情况进行了对比。我们发现，当呼吸脉冲发生时，白矮星核心更大，且中心氧丰度高于呼吸脉冲被抑制的情况，这与先前的研究一致。然而，呼吸脉冲的发生不足以解释最近推导的脉动白矮星星震学模型所特有的较大核心和过高氧丰度。当我们将来自经历过呼吸脉冲的前身星的白矮星与未经历过呼吸脉冲的前身星的白矮星的脉动周期进行比较时，我们发现绝对差异最大可达$\sim 30$秒。

英文摘要：

Breathing pulses are mixing episodes that could develop during the core-helium burning phase of low- and intermediate-mass stars. The occurrence of breathing pulses is expected to bear consequences on the formation and evolution of white dwarfs, particularly on the core chemical structure, which can be probed by asteroseismology. We aim to explore the consequences of breathing pulses on the chemical profiles and pulsational properties of variable white-dwarf stars with hydrogen-rich envelopes, known as ZZ Ceti stars. We compute stellar models with masses of $1.0 M_{\odot}$ and $2.5 M_{\odot}$ in the zero-age main sequence, and evolve them through the core-helium burning phase to the thermal pulses on the asymptotic giant branch, and finally to advanced stages of white-dwarf cooling. We compare the chemical structure of the core of white dwarfs whose progenitors have experienced breathing pulses during the core-helium burning phase with the case in which breathing pulses have not occurred. We find that, when breathing pulses occur, the white-dwarf cores are larger and the central abundances of oxygen are higher than for the case in which the breathing pulses are suppressed, in line with previous studies. However, the occurrence of breathing pulses is not sufficient to explain the large cores and the excessive oxygen abundances that characterize recently derived asteroseismological models of pulsating white dwarfs. We find absolute differences of up to $\sim 30$ seconds when we compare pulsation periods of white dwarfs coming from progenitors that have experienced breathing pulses with the case in which the progenitors have not suffered breathing pulses.

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