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arXiv 0802.4375astro-ph
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短周期软X射线瞬变的演化模型：与观测的比较

Evolutionary models of short-period soft X-ray transients: comparison with observations

L. Yungelson, J. -P. Lasota

备注：
9 pages, 6 figures, replaced to match the version accepted by A&A, 2 new figures, Eq. (3) for the upper limit on mass-transfer rates corrected, more extended discussion, conclusions unchanged
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摘要：

我们考虑短周期（<10小时）低质量黑洞双星（LMBHB）的人口的演化模型，并将它们与软X射线瞬变（SXTs）的观测进行比较。我们表明，假设强烈减少磁制动（如我们以前建议的低质量半独立双星）的计算质量和有效温度的secondaries是非常接近的观测质量和有效温度（从他们的光谱推断）的施主星在短周期LMBHB。如果假设这些系统中的吸积盘被截断（"漏“），则SXTs中的理论传质速率与观测到的一致。我们发现，短周期SXT的人口主要是由系统，其中有未演变或轻微演变的主序施主（$M_2 \lesssim 1.2M_\odot$）与氢丰度的中心$X_c > 0.35$在罗氏瓣溢出（RLOF）。较长周期（0.5 - 1）天）的SXT可能来自初始供体质量约为1 $M_\odot$和$X_c < 0.35$的系统。因此，我们可以解释短周期LMBHB的起源，而不需要引用核心几乎完全耗尽氢的供体。我们的模型表明，除非目前接受的经验估计的质量损失率的风大质量O型星和沃尔夫-拉叶星显着高估，一个非常高的效率的共同包络喷射是必要的，以形成短周期LMBHB。

英文摘要：

We consider evolutionary models for the population of short-period (<10 hr) low-mass black-hole binaries (LMBHBs) and compare them with observations of soft X-ray transients (SXTs). We show that assuming strongly reduced magnetic braking (as suggested by us before for low-mass semidetached binaries) the calculated masses and effective temperatures of secondaries are encouragingly close to the observed masses and effective temperatures (as inferred from their spectra) of donor stars in short-period LMBHBs. Theoretical mass-transfer rates in SXTs are consistent with the observed ones if one assumes that accretion discs in these systems are truncated (``leaky''). We find that the population of short-period SXTs is formed mainly by systems which had unevolved or slightly evolved main-sequence donors ($M_2 \lesssim 1.2M_\odot$) with a hydrogen abundance in the center $X_c > 0.35$ at the Roche-lobe overflow (RLOF). Longer period (0.5 - 1) day) SXTs might descend from systems with initial donor masses of about 1 $M_\odot$ and $X_c < 0.35$. Thus, one can explain the origin of short period LMBHB without invoking donors with cores almost totally depleted of hydrogen. Our models suggest that, unless the currently accepted empirical estimates of mass-loss rates by winds for massive O-stars and Wolf-Rayet stars are significantly over-evaluated, a very high efficiency of common-envelope ejection is necessary to form short-period LMBHBs.

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