矮球状星系中的蓝羽星族：真正的蓝离散星还是年轻的恒星星族？
The blue plume population in dwarf spheroidal galaxies: genuine blue stragglers or young stellar population?
摘要：
节录...蓝离散星（BSS）被认为是原始双星系统或碰撞双星系统的产物。在矮球状星系的背景下，它是很难坚定地解开一个真正的BSS人口从年轻的主序（MS）跟踪一个~1-2 Gyr老恒星形成插曲。假设它们的蓝羽是由BSS组成的，我们用地面和空间测光的汇编估计了8个本星系群非成星矮星系的BSS频率。我们的结果可以概括如下：（i）在任何给定的Mv下，矮星系的BSS频率总是高于相似光度的球状星团的BSS频率;（ii）最低光度矮星系的BSS频率与银河系晕中观测到的BSS频率非常一致;最有趣的是（iii）推导出BSS频率与星系Mv之间的统计显著的反相关。我们的矮星系样本的低密度，几乎没有碰撞的环境使我们能够推断：（i）它们的动力学演化非常低;（ii）碰撞BSS的产生可以忽略不计;因此（iii）它们的蓝色羽流主要由原始双星组成。矮星系的反相关可以作为一个推论：服从反相关的星系更可能拥有真正的原始BSS，而不是年轻的主序星。
英文摘要：
Abridged... Blue stragglers (BSS) are thought to be the product of either primordial or collisional binary systems. In the context of dwarf spheroidal galaxies it is hard to firmly disentangle a genuine BSS population from young main sequence (MS) stars tracing a ~1-2 Gyr old star forming episode. Assuming that their blue plume populations are made of BSS, we estimate the BSS frequency for 8 Local Group non star-forming dwarf galaxies, using a compilation of ground and space based photometry. Our results can be summarized as follows: (i) The BSS frequency in dwarf galaxies, at any given Mv, is always higher than that in globular clusters of similar luminosities; (ii) the BSS frequency for the lowest luminosity dwarf galaxies is in excellent agreement with that observed in the Milky Way halo; and most interestingly (iii) derive a statistically significant anti-correlation between the BSS frequency and the galaxy Mv. The low density, almost collision-less, environments of our dwarf galaxy sample allow us to infer (i) their very low dynamical evolution; (ii) a negligible production of collisional BSS; and consequently (iii) that their blue plumes are mainly made of primordial binaries. The dwarf galaxies anti-correlation can be used as a discriminator: galaxies obeying the anti-correlation are more likely to possess genuine primordial BSS rather than young main sequence stars.
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