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arXiv 2301.12992astro-ph.SR
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演化的激变变星作为AM CVn星的祖先

Evolved cataclysmic variables as progenitors of AM CVn stars

Arnab Sarkar, Hongwei Ge, Christopher A. Tout

备注：
15 pages, 15 figures. Accepted for publication in MNRAS
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摘要：

我们的模型激变变量（CV）与太阳金属量捐助者（$X=0.7,\:Z=0.02$），演变形成AM CVn星通过演变CV形成通道使用各种角动量损失机制的磁制动（$\mathrm{AML_{MB}}$）。我们发现，在我们的双发电机（DD）模型的时间尺度$\mathrm{AML_{MB}}$是短于以前使用的经验公式。由于DD模型的时间尺度较短，形成AM CVn星的初始条件参数空间较大。我们对通过Evolved CV通道形成的AM CVn星的预期数量进行了分析，发现AM CVn星的数量大约是之前报道的$3$的两倍。我们发展这些系统的详细与剑桥恒星演化代码（STARS），并表明，进化CV填充一个区域的轨道周期$P_\mathrm{orb}\geq5.5\,\mathrm{hr}$。我们发展我们的捐助者超出他们的轨道周期最小值，并发现一个显着的数字成为极端H耗尽系统。这使得它们与从He星和白矮星（WD）通道演化而来的系统在光谱中没有H的情况下无法区分。我们还比较了质量，质量转移率的捐助者，和轨道周期与观测。我们发现，在YZ LMi和V396 Hya等系统中，供体的状态和H的缺乏与我们的建模轨迹相匹配，而CR Boo和HP Lib等系统与我们的建模轨迹相匹配，如果它们的实际供体质量位于观测质量范围的低端。

英文摘要：

We model cataclysmic variables (CVs) with solar metallicity donors ($X=0.7,\:Z=0.02$) that evolve to form AM CVn stars through the Evolved CV formation channel using various angular momentum loss mechanisms by magnetic braking ($\mathrm{AML_{MB}}$). We find that the time-scale for $\mathrm{AML_{MB}}$ in our double-dynamo (DD) model is shorter than that of previously used empirical formulae. Owing to the shorter time-scales, a larger parameter space of initial conditions evolves to form AM CVn stars with the DD model than with other models. We perform an analysis of the expected number of AM CVn stars formed through the Evolved CV channel and find about $3$ times as many AM CVn stars as reported before. We evolve these systems in detail with the Cambridge stellar evolution code (STARS) and show that evolved CVs populate a region with orbital period $P_\mathrm{orb}\geq5.5\,\mathrm{hr}$. We evolve our donors beyond their orbital period minimum and find that a significant number become extremely H-exhausted systems. This makes them indistinguishable from systems evolved from the He-star and the White Dwarf (WD) channels in terms of the absence of H in their spectra. We also compare the masses, mass-transfer rates of the donor, and the orbital period with observations. We find that the state of the donor and the absence of H in systems such as YZ LMi and V396 Hya match with our modelled trajectories, while systems such as CR Boo and HP Lib match with our modelled tracks if their actual donor mass lies on the lower-end of the observed mass range.

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