A carbon dwarf wearing a Necklace: first proof of accretion in a post-common-envelope binary central star of a planetary nebula with jets
A carbon dwarf wearing a Necklace: first proof of accretion in a post-common-envelope binary central star of a planetary nebula with jets
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戴着项链的碳矮星：第一个在具有喷流的行星状星云的后共包层双星中心恒星中吸积的证据
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发表时间：
2012
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通讯作者：
R. Corradi
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作者：
B. Miszalski;H. Boffin;R. Corradi
行星状星云（PNe）中的准直外流或喷流的形成还没有很好的理解。没有证据表明PNe中存在活跃的吸积盘，因此很难决定几种建议的射流形成情景中哪一种可能是正确的。已知有少数PNe的中央宽联星有吸积碳和慢中子俘获（s-process）增强的物质，是钡星的直接祖先;然而，没有已知的近距离联星类似物经历过共包络（CE）阶段。在这里，我们提出了光谱的项链采取近光变曲线的最低点，第一次揭示了一个富碳（C/O > 1）的同伴，碳矮星，在后CE中央星星。由于未进化的恒星不产生碳，因此次级恒星的化学增强只能通过来自初级恒星的吸积来解释。由于在短暂的CE阶段没有足够的物质可以被吸积，因此最有可能在CE阶段之前通过风吸积发生吸积。项链中的一对喷流，被观察到比PN更古老，因此很可能是在早期吸积阶段从伴星周围的吸积盘发射的。这一发现增加了重要的重量新兴的情况下，喷流在后CE PNe主要是由吸积盘周围的主序伴星在CE阶段之前推出。
The formation of collimated outflows or jets in planetary nebulae (PNe) is not well understood. There is no evidence for active accretion discs in PNe, making it difficult to decide which of the several proposed jet formation scenarios may be correct. A handful of wide binary central stars of PNe are known to have accreted carbon and slow neutron capture (s-process) enhanced material, the immediate progenitors of barium stars; however, no close binary analogues are known to have passed through a common-envelope (CE) phase. Here we present spectroscopy of the Necklace taken near light-curve minimum that for the first time reveals a carbon-rich (C/O > 1) companion, a carbon dwarf, in a post-CE central star. As unevolved stars do not produce carbon, the chemical enhancement of the secondary can only be explained by accretion from the primary. Accretion most likely happened prior to the CE phase via wind accretion as not enough material can be accreted during the short CE phase. The pair of jets in the Necklace, which are observed to be older than the PN, are therefore likely to have been launched from an accretion disc around the companion during this early accretion phase. This discovery adds significant weight to the emerging scenario that jets in post-CE PNe are primarily launched by an accretion disc around a main-sequence companion before the CE phase.