双星演化导致两个白矮星伴星群体
Binary Evolution Leads to Two Populations of White Dwarf Companions
摘要：
行星和其他低质量的双星伴星面临着各种潜在的命运，因为它们的宿主恒星离开主序星，成长为亚巨星和巨星。恒星的质量损失往往会使轨道扩大，而潮汐力矩往往会使轨道缩小，有时会达到伴星直接被主星吞没的程度。此外，一旦被吞噬，随之而来的共同包层（CE）阶段可能会导致伴星完全融入主星的包层;或者，如果伴星足够大，它可以转移足够的能量来弹出包层，并保持在围绕白矮星核心的紧密轨道上。因此，普通的双星演化应该会导致白矮星周围有两种主要的行星群：一种是经过CE阶段并处于短周期轨道的行星，另一种是完全避开CE并处于长周期轨道的行星。
英文摘要：
Planets and other low-mass binary companions to stars face a variety of potential fates as their host stars move off the main sequence and grow to subgiants and giants. Stellar mass loss tends to make orbits expand, and tidal torques tend to make orbits shrink, sometimes to the point that a companion is directly engulfed by its primary. Furthermore, once engulfed, the ensuing common envelope (CE) phase can result in the companion becoming fully incorporated in the primary's envelope; or, if the companion is massive enough, it can transfer enough energy to eject the envelope and remain parked in a tight orbit around the white dwarf core. Therefore, ordinary binary evolution ought to lead to two predominant populations of planets around white dwarfs: those that have been through a CE phase and are in short-period orbits, and those that have entirely avoided the CE and are in long-period orbits.
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