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arXiv 1607.02148astro-ph.HE
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合并中子星双星中的出生反冲和时间延迟--对超暗矮星和Milky Way中r-过程核合成的影响

Natal Kicks and Time Delays in Merging Neutron Star Binaries - Implications for r-process nucleosynthesis in Ultra Faint Dwarfs and in the Milky Way

Paz Beniamini, Kenta Hotokezaka, Tsvi Piran

摘要:

合并的中子星双星是重r过程核合成的主要候选源。重r-过程物质的数量与物质抛射和合并率一致,遗迹放射性物质的丰度表明,重r-过程物质是在罕见的事件中产生的。对可能的macronovae的观测为这个模型提供了进一步的支持。不过,一些担忧依然存在。一个是在超暗矮星(UFD)星系中观测到重r过程元素。UFD的逃逸速度是如此之小,以至于在中子星诞生时发生的出生撞击可能会将这样的双星从UFD中弹射出来。此外,UFD的旧恒星星族要求r-过程核合成必须在很早的时候发生,而致密双星可能需要几个Gyr才能合并。这最后一个问题也出现在银河系内,在一些低金属丰度的恒星中观察到了重r过程物质。我们在这里表明,由于相当一部分中子星双星的形成与一个非常小的自行,这些将不会被弹出,甚至从UFD。此外,这些双星中有很大一部分在几百万年内合并,在某些情况下,合并时间甚至短于一百万年。这种“快速合并”的人口解释了UFD和银河系中重r过程材料的出现。

英文摘要:

Merging neutron star binaries are prime candidate sources for heavy r-process nucleosynthesis. The amount of heavy r-process material is consistent with the mass ejection and rates of mergers, and abundances of relic radioactive materials suggest that heavy r-process material is produced in rare events. Observations of possible macronovae provide further support for this model. Still, some concerns remain. One is the observation of heavy r-process elements in Ultra Faint Dwarf (UFD) galaxies. The escape velocities from UFDs are so small that the natal kicks, taking place at neutron stars birth, might eject such binaries from UFDs. Furthermore the old stellar populations of UFDs requires that r-process nucleosynthesis must have taken place very early on, while it may take several Gyr for compact binaries to merge. This last problem arises also within the Milky Way where heavy r-process materials has been observed in some low metallicity stars. We show here that since a significant fraction of neutron star binaries form with a very small proper motion those won't be ejected even from a UFD. Furthermore, a significant fraction of these binaries merge within a few hundred Myr and in some cases the merger time is even shorter than a hundred Myr. This population of "rapid mergers" explains the appearance of heavy r-process material in both UFDs and in the Milky Way.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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