Mass transfer variation in the outburst model of dwarf novae and soft X-ray transients
Mass transfer variation in the outburst model of dwarf novae and soft X-ray transients
复制标题
矮新星爆发模型中的质量传递变化和软X射线瞬变
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
J. Hameury
中科院分区：
文献类型：
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作者：
M. Viallet;J. Hameury
上下文。在软X射线瞬变和矮新星爆发的圆盘不稳定性模型的标准公式中，假定次级物质的传质速率是恒定的。这看起来似乎很自然，因为L1点仍然被吸积盘遮挡住了吸积光度。然而，可能会发生间接加热，并可能导致传质速率的提高。在爆炸过程中，这种传质速率的增强是否是当前模型中缺失的一部分，目前仍有争议。目标。我们讨论了在爆发期间导致传质速率增强的两种机制：热的外盘边缘本身可以显著地加热L1点；光学薄流出物质的散射辐射也可以显著地加热L1点。我们定量地确定了额外加热引起的传质速率的增加。方法：研究方法。我们用解析和数值的方法估计了圆盘边缘对L1点的加热。由圆盘上方的物质散射的光度的比例，在这里被建模为球对称的流出，是通过解析确定的。最后，我们用数值方法求解了次星的垂直结构方程，并计算了质量传递增强。结果。爆发时，盘外边缘的温度可达104K。盘边缘用本征恒星通量量级的通量加热次级天体的上层。这可能对传质速率没有太大影响。在软X射线瞬变中，圆盘的环境介质(日冕+风)可能会将一定比例的吸积光度向L1反向散射。在矮新星中，同样的影响可能是由于爆发期间的风造成的。由于软X射线瞬变达到高亮度，即使这种效应的低效率也能产生显著的L1加热，而我们表明在矮新星中这种影响可以忽略不计。最初，入射的辐射不会穿透次要天体的光球层。根据加热效率(这一点必须确定)，传质速率可能会显著提高。
Context. In the standard formulation of the disc instability model for soft X-ray transient and dwarf nova outbursts, the mass transfer rate from the secondary is assumed to be constant. This may seem natural since the L1 point remains shielded from the accretion luminosity by the accretion disc. However an indirect heating could take place and could lead to an enhancement of the mass transfer rate. It is still debated whether such an enhancement of the mass transfer rate during outbursts is a missing ingredient of the current model. Aims. We discuss two mechanisms that could result in an enhancement of the mass transfer rate during outbursts: the hot outer disc rim itself could significantly heat the L1 point; scattered radiation by optically thin outflowing matter could also heat L1 significantly. We determine quantitatively the increase of the mass transfer rate resulting from an extra heating. Methods. We estimate the heating of the L1 point by the disc rim by analytical and numerical arguments. The fraction of the luminosity scattered by matter above the disc, here modeled as a spherically symmetric outflow, is determined analytically. We finally solve in a numerical way the vertical structure equations for the secondary star and calculate the mass transfer enhancement. Results. During outbursts, the temperature at the outer edge of the disc reaches 10 4 K. The disc edge heats up the upper layer of the secondary with a flux of the order of the intrinsic stellar flux. This probably has no large effect on the mass transfer rate. In soft X-ray transients, the environing medium of the disc (corona+wind) could back-scatter a certain fraction of the accretion luminosity toward L1. In dwarf novae, the same effect could be due to the wind present during outburst. Since soft X-ray transients reach high luminosities, even a low efficiency of this effect could yield a significant heating of L1, whereas we show that in dwarf novae this effect is negligible. Initially the incoming radiation does not penetrate below the photosphere of the secondary. Depending on the heating efficiency, which has to be determined, the mass transfer rate could be significantly increased.