A wide binary trigger for white dwarf pollution
A wide binary trigger for white dwarf pollution
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DOI：
10.1093/mnras/stv1913
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发表时间：
2015-11-21
影响因子：
4.8
通讯作者：
Veras, Dimitri
中科院分区：
文献类型：
--
作者：
Bonsor, Amy;Veras, Dimitri
白色矮星大气中的金属污染通常被认为是残留行星系统的标志。对这种污染的大多数解释都预测，具有白色矮冷却年龄的污染系统的数量会急剧减少。观测结果并没有证实这一趋势，而老（1-5 Gyr）白色矮星的金属污染也很难解释。我们提出了一种替代的，时间无关的机制，产生的白色矮星污染。一个宽的双星伴星的轨道可能会受到银河潮汐的扰动，在白色矮分支经过数十亿年的演化后，这是第一次接近主星星。我们表明，这样一个接近的方法扰动行星系统的轨道白色矮星，散射星子的恒星掠食轨道，在某种程度上，可能会污染白色矮星的大气。我们的估计发现，这种机制可能有助于金属污染，以及其他机制，在高达百分之几的观测样本的白色矮星与广泛的二元伴侣，独立的白色矮星的年龄。这种年龄的独立性是这个广泛的二元机制与文献中提出的解释白色矮星污染的其他机制之间的关键区别。目前的观测样本还不够大，无法评估这种机制是否对污染的白色矮星的数量有重大贡献，因此需要对宽双星的数量进行更好的限制，例如在不久的将来将获得的盖亚。
Metal pollution in white dwarf atmospheres is commonly assumed to be a signature of remnant planetary systems. Most explanations for this pollution predict a sharp decrease in the number of polluted systems with white dwarf cooling age. Observations do not confirm this trend, and metal pollution in old (1-5 Gyr) white dwarfs is difficult to explain. We propose an alternative, time-independent mechanism to produce the white dwarf pollution. The orbit of a wide binary companion can be perturbed by Galactic tides, approaching close to the primary star for the first time after billions of years of evolution on the white dwarf branch. We show that such a close approach perturbs a planetary system orbiting the white dwarf, scattering planetesimals on to star-grazing orbits, in a manner that could pollute the white dwarf's atmosphere. Our estimates find that this mechanism is likely to contribute to metal pollution, alongside other mechanisms, in up to a few per cent of an observed sample of white dwarfs with wide binary companions, independent of white dwarf age. This age independence is the key difference between this wide binary mechanism and others mechanisms suggested in the literature to explain white dwarf pollution. Current observational samples are not large enough to assess whether this mechanism makes a significant contribution to the population of polluted white dwarfs, for which better constraints on the wide binary population are required, such as those that will be obtained in the near future with Gaia.