论文标题
M15的星星与R-Process一起出生
The Stars in M15 Were Born with the r-process
论文作者
论文摘要
球状簇M15的红色巨型分支（RGB）上恒星的高分辨率光谱表明，R-Process元素（如BA和EU）的丰富性中有大量（〜1个DEX）分散体。已经提出了中子星合并（NSM）作为R过程的主要来源。但是，大多数NSM模型的延迟时间比集群形成的时间尺度更长。一种可能性是，NSM在聚类完成后很长一段时间内M15中污染了恒星的表面。在这种情况下，随着恒星打开RGB，污染元素的丰富度将减少。我们在整个RGB和主序列的顶部呈现了66颗恒星中BA的Keck/Deimos丰度。 BA丰度没有出色的光度（进化阶段）。因此，恒星天生就有今天的BA，而BA并未源于延迟时间的源，而不是集群形成时间尺度。特别是，如果BA的来源是中子星的合并，那将有很短的延迟时间。另外，如果BA富集发生在集群形成之前，则Ba丰度的不均匀性需要能够在形成M15的气云的长度尺度上持续存在，这不太可能。
High-resolution spectroscopy of stars on the red giant branch (RGB) of the globular cluster M15 has revealed a large (~1 dex) dispersion in the abundances of r-process elements, like Ba and Eu. Neutron star mergers (NSMs) have been proposed as a major source of the r-process. However, most NSM models predict a delay time longer than the timescale for cluster formation. One possibility is that a NSM polluted the surfaces of stars in M15 long after the cluster finished forming. In this case, the abundances of the polluting elements would decrease in the first dredge-up as stars turn on to the RGB. We present Keck/DEIMOS abundances of Ba in 66 stars along the entire RGB and the top of the main sequence. The Ba abundances have no trend with stellar luminosity (evolutionary phase). Therefore, the stars were born with the Ba they have today, and Ba did not originate in a source with a delay time longer than the timescale for cluster formation. In particular, if the source of Ba was a neutron star merger, it would have had a very short delay time. Alternatively, if Ba enrichment took place before the formation of the cluster, an inhomogeneity of a factor of 30 in Ba abundance needs to be able to persist over the length scale of the gas cloud that formed M15, which is unlikely.
