仙境传说的预言：吞噬世界的渐近巨人和白矮星的遗传
Foretellings of Ragnarök: World-engulfing Asymptotic Giants and the Inheritance of White Dwarfs
摘要：
在白矮星周围寻找行星，以及以大气污染和星周盘的形式存在的动力学不稳定性的证据，提出了关于行星系的性质的问题，这些行星系可以在渐近巨星分支（AGB）的变迁中幸存下来。我们研究了竞争的影响，在几个AU的行星从恒星，强大的潮汐力所产生的恒星的大对流信封，和行星的轨道膨胀，由于恒星质量损失。我们，第一次，研究行星的演化，同时遵循AGB上的每个热脉冲。对于类木行星来说，潮汐力很强，并且可以在1 M_Sol恒星的约3 AU和5 M_Sol恒星的约5 AU处将行星拉入包络。质量较低的行星感受到较弱的潮汐力，最初在1.5-3 AU范围内的类地行星进入恒星包层。因此，在最大恒星半径内开始的低质量行星可以生存，因为它们的轨道由于质量损失而扩大。包含一个中等的行星偏心率稍微加强了类木行星所经历的潮汐力。偏心的类地行星风险更大，因为它们的偏心率不会衰减，而且它们的近心点很小，把它们带进了恒星的包层。我们还找到了在白矮星周围发现行星的最近半径，假设任何进入恒星包层的行星都被摧毁了。在这种情况下，行星不太可能被发现在大约1.5天文单位的白矮星与1 M_Sol的祖先和大约10天文单位的白矮星与5 M_Sol的祖先。
英文摘要：
The search for planets around White Dwarf stars, and evidence for dynamical instability around them in the form of atmospheric pollution and circumstellar discs, raises questions about the nature of planetary systems that can survive the vicissitudes of the Asymptotic Giant Branch (AGB). We study the competing effects, on planets at several AU from the star, of strong tidal forces arising from the star's large convective envelope, and of the planets' orbital expansion due to stellar mass loss. We, for the first time, study the evolution of planets while following each thermal pulse on the AGB. For Jovian planets, tidal forces are strong, and can pull into the envelope planets initially at ~3 AU for a 1M_Sol star and ~5 AU for a 5M_Sol star. Lower-mass planets feel weaker tidal forces, and Terrestrial planets initially within 1.5-3 AU enter the stellar envelope. Thus, low-mass planets that begin inside the maximum stellar radius can survive, as their orbits expand due to mass loss. The inclusion of a moderate planetary eccentricity slightly strengthens the tidal forces experienced by Jovian planets. Eccentric Terrestrial planets are more at risk, since their eccentricity does not decay and their small pericentre takes them inside the stellar envelope. We also find the closest radii at which planets will be found around White Dwarfs, assuming that any planet entering the stellar envelope is destroyed. Planets are in that case unlikely to be found inside ~1.5 AU of a White Dwarf with a 1M_Sol progenitor and ~10 AU of a White Dwarf with a 5M_Sol progenitor.
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