Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems
Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems
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DOI：
10.1093/mnras/stx2664
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发表时间：
2018-02-01
影响因子：
4.8
通讯作者：
Stone, N.
中科院分区：
文献类型：
--
作者：
Farihi, J.;Fossati, L.;Stone, N.
本文报道了包括WD 1145+017在内的几个污染白色矮星的圆偏振光谱和X射线观测结果，目的是限制这些演化行星系统中盘物质的行为和瞬时吸积率。先前观察到塞曼分裂的两颗恒星WD 0322-019和WD 2105-820的检测值高于5 sigma且< B-z >> 1 kG，而WD 1145+017、WD 1929+011和WD 2326+049的检测值低于该最低置信度。对于后三颗恒星，高分辨率光谱和大气模型被用来获得磁场强度的限制，通过塞曼分裂的情况下，发现B-* < 20 kG的基础上的数据与分辨率R接近40 000。本文提出了一个分析框架，用于分析落在白色矮星磁极区的大块地球组成物质，在那里X射线和回旋辐射可能有助于吸积光度。这种分析适用于WD 1145+017，WD 1729+371，和WD 2326+049的X射线数据，和上限计数率建模与等离子体的范围kT = 1-10 keV的磁性和非磁性吸积制度的光谱。所有三颗恒星的结果都与典型的尘埃白色矮星在108-109 g s（-1）的稳定状态相一致。特别是，WD 1145+017的非磁性极限被发现远低于先前估计的10（12）g s（-1），并且可能低于1010 g s（-1），因此表明星盘系统可能在其演化状态中是平均的，并且仅在观察几何学上是特殊的。
This paper reports circular spectropolarimetry and X-ray observations of several polluted white dwarfs including WD 1145+017, with the aim to constrain the behaviour of disc material and instantaneous accretion rates in these evolved planetary systems. Two stars with previously observed Zeeman splitting, WD 0322-019 and WD 2105-820, are detected above 5 sigma and < B-z > > 1 kG, while WD 1145+017, WD 1929+011, and WD 2326+049 yield (null) detections below this minimum level of confidence. For these latter three stars, high-resolution spectra and atmospheric modelling are used to obtain limits on magnetic field strengths via the absence of Zeeman splitting, finding B-* < 20 kG based on data with resolving power R approximate to 40 000. An analytical framework is presented for bulk Earth composition material falling on to the magnetic polar regions of white dwarfs, where X-rays and cyclotron radiation may contribute to accretion luminosity. This analysis is applied to X-ray data for WD 1145+017, WD 1729+371, and WD 2326+049, and the upper bound count rates are modelled with spectra for a range of plasma kT = 1-10 keV in both the magnetic and non-magnetic accretion regimes. The results for all three stars are consistent with a typical dusty white dwarf in a steady state at 108-109 g s(-1). In particular, the non-magnetic limits for WD 1145+017 are found to be well below previous estimates of up to 10(12) g s(-1), and likely below 1010 g s(-1), thus suggesting the star-disc system may be average in its evolutionary state, and only special in viewing geometry.