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arXiv 0801.3433astro-ph
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具有黑洞成分的低质量双星的演化

Evolution of low-mass binaries with black-hole components

L. Yungelson, J. -P. Lasota

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(SXT)的观测结果进行比较。LMBHB的演化取决于施主的核演化和/或施主星风和引力波辐射的磁制动引起的轨道角动量损失。我们表明,没有观察到稳定的发光LMBHB意味着,在RLOF的低质量捐助者的角动量损失大幅减少相对于Verbunt和Zwaan的“标准”处方磁制动。在此假设下,质量和有效温度的LMBHB的模型秒数是在一个令人满意的协议与质量和有效温度(从他们的光谱推断)的观察到的施主在LMBHB。如果假设这些系统中的吸积盘被截断(“泄漏”),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种群主要是由在RLOF具有未进化或轻微进化(X_c > 0.35)施主的系统形成的。当初始施主质量约为1个太阳质量且X_c < 0.35时,SXT的周期可能较长(0.5 - 1天)。没有必要援引几乎氢耗尽核的供体来解释LMBHB的起源。我们的模型表明,一个非常高的效率,共同的信封喷射是必要的,以形成LMBHB,除非目前普遍接受的经验估计的质量损失率风前WR和WR-明星显着高估。

英文摘要:

We consider evolutionary models for the population of short-period (<10 hr) low-mass black-hole binaries (LMBHB) and compare them with observations of soft X-ray transients (SXT). Evolution of LMBHB is determined by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking by the stellar wind of the donors and gravitational wave radiation. We show that the absence of observed stable luminous LMBHB implies that upon RLOF by the low-mass donor angular momentum losses are substantially reduced with respect to the Verbunt and Zwaan "standard" prescription for magnetic braking. Under this assumption masses and effective temperatures of the model secondaries of LMBHB are in a satisfactory agreement with the masses and effective temperatures (as inferred from their spectra) of the observed donors in LMBHB. 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 SXT is formed mainly by systems which had unevolved or slightly evolved (X_c > 0.35) donors at the RLOF. Longer period (0.5 - 1 day) SXT might descend from systems with initial donor mass about 1 solar and X_c < 0.35. It is unnecessary to invoke donors with almost hydrogen-depleted cores to explain the origin of LMBHB. Our models suggest that a very high efficiency of common-envelopes ejection is necessary to form LMBHB, unless currently commonly accepted empirical estimates of mass-loss rates by winds for pre-WR and WR-stars are significantly over-evaluated.

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