周期反弹候选体BW Sculptoris中的褐矮星供体与具有复杂流撞击区的光学薄吸积盘
A brown dwarf donor and an optically thin accretion disc with a complex stream impact region in the period-bouncer candidate BW Sculptoris
AI总结：
本文通过对周期反弹候选体BW Scl的多历元光谱与测光分析，测定其白矮星质量为0.85 M⊙、供体为质量仅0.051 M⊙的褐矮星，并揭示了低光度光学薄吸积盘及复杂热斑结构，为理解该系统的演化状态提供了关键观测约束。
摘要：
我们提出了对WZ Sge型矮新星BW Scl的多历元光谱和测光观测的分析，BW Scl是一个周期反弹候选体。我们探测到了来自供体星的多条辐照诱导发射线，从而能够高精度地测量径向速度变化。此外，利用起源于吸积白矮星光球层的Mgii 4481和Caii K吸收线，我们测量了白矮星的径向速度半振幅及其引力红移。我们发现该白矮星的质量为0.85±0.04 M⊙，而供体星是一个质量为0.051±0.006 M⊙的低质量天体，远低于氢燃烧极限。利用近红外数据，我们将供体星的有效温度上限设定为≲1600 K，对应于T光谱型的褐矮星。BW Scl中的光学薄吸积盘具有非常低的光度≲4×10^30 erg s^-1，这对应于非常低的质量吸积率≲7×10^-13 M⊙ year^-1。吸积盘的外部区域密度很低，允许物质流向下流动到内盘区域。热斑最亮的部分位于吸积盘的圆化半径附近。该热斑是光学厚的，并具有复杂的、拉长的结构。基于所测量的系统参数，我们讨论了该系统的演化状态。
英文摘要：
We present an analysis of multi-epoch spectroscopic and photometric observations of the WZ Sge-type dwarf nova BW Scl, a period-bouncer candidate. We detected multiple irradiation-induced emission lines from the donor star allowing the radial velocity variations to be measured with high accuracy. Also, using the absorption lines Mgii 4481 and Caii K originated in the photosphere of the accreting white dwarf (WD), we measured the radial velocity semi-amplitude of the WD and its gravitational redshift. We find that the WD has a mass of 0.85$\pm$0.04 M$_\odot$, while the donor is a low-mass object with a mass of 0.051$\pm$0.006 M$_\odot$, well below the hydrogen-burning limit. Using NIR data, we put an upper limit on the effective temperature of the donor to be $\lesssim$1600 K, corresponding to a brown dwarf of T spectral type. The optically thin accretion disc in BW Scl has a very low luminosity $\lesssim$4 $\times 10^{30}$ erg s$^{-1}$ which corresponds to a very low mass accretion rate of $\lesssim$7 $\times 10^{-13}$ M$_\odot$ year$^{-1}$. The outer parts of the disc have a low density allowing the stream to flow down to the inner disc regions. The brightest part of the hotspot is located close to the circularization radius of the disc. The hotspot is optically thick and has a complex, elongated structure. Based on the measured system parameters, we discuss the evolutionary status of the system.
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