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arXiv 2008.05476astro-ph.HEastro-ph.SR
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大质量双星系统中潮汐耗散对共包络相位偏心起始的影响

Tidal Dissipation Impact on the Eccentric Onset of Common Envelope Phases in Massive Binary Star Systems

Michelle Vick, Morgan MacLeod, Dong Lai, Abraham Loeb

摘要:

在巨恒星的对流区中,由于湍流粘性引起的潮汐耗散在形成前共包层系统的轨道中起着重要的作用。这样的系统可能是瞬变源和紧密的双星系统,最终将合并并产生可检测的引力波信号。以往对共包层事件发生的研究主要集中在圆轨道和同步旋转的施主星上,假设潮汐耗散可以在双星到达Roche瓣溢出(RLO)之前快速旋转主星并使轨道圆化。我们通过将恒星主序后恒星演化的数值模型与Vick & Lai(2020)$-$中开发的对流包络中的潮汐耗散模型相结合来测试这一假设,该潮汐模型即使对于近心点距离较小的高偏心轨道也是准确的。我们发现,在许多情况下,潮汐耗散不圆化RLO之前的轨道。对于一颗$10~M_\odot$($15~M_\odot$)主星与一颗$1.4~M_\odot$伴星的相互作用,当主星离开主序星时,近心距离在3天文单位(6天文单位)以内的系统将在主星增长到罗氏半径时保持初始轨道偏心率。即使在RLO之前潮汐循环的系统中,供体星也可能在质量转移开始时亚同步旋转。我们的结果表明,一些可能的双中子星系统的前兆可能是偏心的罗氏半径。预共包络偏心率对所产生的致密双星的影响值得进一步研究。

英文摘要:

Tidal dissipation due to turbulent viscosity in the convective regions of giant stars plays an important role in shaping the orbits of pre-common envelope systems. Such systems are possible sources of transients and close compact binary systems that will eventually merge and produce detectable gravitational wave signals. Most previous studies of the onset of common envelope episodes have focused on circular orbits and synchronously rotating donor stars under the assumption that tidal dissipation can quickly spin up the primary and circularize the orbit before the binary reaches Roche-lobe overflow (RLO). We test this assumption by coupling numerical models of the post main sequence stellar evolution of massive-stars with the model for tidal dissipation in convective envelopes developed in Vick & Lai (2020) $-$ a tidal model that is accurate even for highly eccentric orbits with small pericentre distances. We find that, in many cases, tidal dissipation does not circularize the orbit before RLO. For a $10~M_\odot$ ($15~M_\odot$) primary star interacting with a $1.4~M_\odot$ companion, systems with pericentre distances within 3 AU (6 AU) when the primary leaves the main sequence will retain the initial orbital eccentricity when the primary grows to the Roche radius. Even in systems that tidally circularize before RLO, the donor star may be rotating subsynchronously at the onset of mass transfer. Our results demonstrate that some possible precursors to double neutron star systems are likely eccentric at the Roche radius. The effects of pre-common envelope eccentricity on the resulting compact binary merit further study.

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