Infrared observations of white dwarfs and the implications for the accretion of dusty planetary material
Infrared observations of white dwarfs and the implications for the accretion of dusty planetary material
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DOI：
10.1093/mnras/stx425
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发表时间：
2017-06-01
影响因子：
4.8
通讯作者：
van Lieshout, Rik
中科院分区：
文献类型：
--
作者：
Bonsor, Amy;Farihi, Jay;van Lieshout, Rik
金属污染的白矮星周围的红外线过量与尘埃行星物质的吸积有关。这项工作分析了白矮星无偏差样本的可用红外数据，并证明不超过 3.3% 的白矮星可以拥有宽阔、平坦、不透明的尘埃盘，延伸至罗希半径，盘内边缘的温度为 T-in = 1400 K，这是观测到的过量现象的标准模型。这与约30%的污染发生率形成鲜明对比。我们根据污染白矮星的恒星特性和推断的吸积率，提出了污染白矮星中没有红外线过量的四个潜在原因：（i）它们的尘埃盘是不透明的，但很窄，因此如果超过85％的污染白矮星的尘埃盘窄于δ r < 0.04r，则可以逃避检测，（ii）它们的尘埃盘已完全消耗，这只适用于最古老的白矮星下沉时间尺度超过数百年，（iii）它们的尘埃在光学上很薄，如果以（Poynting-Robertson）PR阻力为主，则可以提供< 10(7) gs(-1)的低吸积率，如果物质向内传输得到增强，则可以提供更高的吸积率，例如由于气体的存在，(iv) 它们的吸积是由纯气体盘提供的，这可能是由于 T-* > 20 000 K 时光学薄尘埃的升华造成的。未来对微弱红外过量或气体存在敏感的观测可以测试这里提出的场景，从而更好地限制污染白矮星中吸积物质的性质。
Infrared excesses around metal-polluted white dwarfs have been associated with the accretion of dusty planetary material. This work analyses the available infrared data for an unbiased sample of white dwarfs and demonstrates that no more than 3.3 per cent can have a wide, flat, opaque dust disc, extending to the Roche radius, with a temperature at the disc inner edge of T-in = 1400 K, the standard model for the observed excesses. This is in stark contrast to the incidence of pollution of about 30 per cent. We present four potential reasons for the absence of an infrared excess in polluted white dwarfs, depending on their stellar properties and inferred accretion rates: (i) their dust discs are opaque, but narrow, thus evading detection if more than 85 per cent of polluted white dwarfs have dust discs narrower than delta r < 0.04r, (ii) their dust discs have been fully consumed, which only works for the oldest white dwarfs with sinking time-scales longer than hundreds of years, (iii) their dust is optically thin, which can supply low accretion rates of < 10(7) gs(-1) if dominated by (Poynting-Robertson) PR-drag, and higher accretion rates, if inwards transport of material is enhanced, e.g. due to the presence of gas, (iv) their accretion is supplied by a pure gas disc, which could result from the sublimation of optically thin dust for T-* > 20 000 K. Future observations sensitive to faint infrared excesses or the presence of gas can test the scenarios presented here, thereby better constraining the nature of the material fuelling accretion in polluted white dwarfs.