原始调查-- XVII。C-19流是动态热的，并且比以前认为的更长
The Pristine survey -- XVII. The C-19 stream is dynamically hot and more extended than previously thought
摘要：
C-19流是迄今发现的最贫金属的恒星系统，平均金属丰度为$[Fe/H] = -3.38\pm0.06$。它的低金属丰度分散度（$σ_{\rm [Fe/H]}$ $<$ 0.18，95%置信水平）以及钠丰度的变化强烈表明球状星团的起源。在这项工作中，我们使用VLT/UVES光谱的7个C-19恒星，以获得更精确的速度测量的成员星，并确定两个新的成员与径向速度和金属丰度符合流的属性。其中一颗新成员星位于距离先前发现的C-19主体30 $°$的位置，这意味着该恒星流比先前已知的要长得多，并且可能有更多的成员等待发现。在C-19的主要部分，我们测量了径向速度色散$σ_v$ = 6.2 $^{+2.0}_{-1.4}$ km s $^{-1}$从9个成员，和流宽度为0.56 $°\pm0.08°$，相当于$\sim$ 158 pc在日心距离为18 kpc。这些证实了C-19在动力学上比其他已知的球状星团流相对更热，并且具有微弱的矮星系流的特性。另一方面，新观测到的三颗明亮成员星的Na丰度变化，其中两颗的Mg和Al丰度变化，以及一颗可以测量的恒星的正常Ba丰度，为球状星团的起源提供了进一步的证据。C-19的动力学和化学性质之间的紧张关系表明，它的祖先经历了复杂的出生环境或破坏历史。
英文摘要：
The C-19 stream is the most metal poor stellar system ever discovered, with a mean metallicity $[Fe/H] = -3.38\pm0.06$. Its low metallicity dispersion ($σ_{\rm [Fe/H]}$ $<$ 0.18 at the 95\% confidence level) as well as variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use VLT/UVES spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream's properties. One of these new member stars is located 30 $°$ away from the previously identified body of C-19, implying that the stream is significantly more extended than previously known and that more members likely await discovery. In the main part of C-19, we measure a radial velocity dispersion $σ_v$ = 6.2$^{+2.0}_{-1.4}$ km s$^{-1}$ from nine members, and a stream width of 0.56$°\pm0.08°$, equivalent to $\sim$158 pc at a heliocentric distance of 18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than other known globular cluster streams and shares the properties of faint dwarf galaxy streams. On the other hand, the variations in the Na abundances of the three newly observed bright member stars, the variations in Mg and Al for two of them, and the normal Ba abundance of the one star where it can be measured provide further evidence for a globular cluster origin. The tension between the dynamical and chemical properties of C-19 suggests that its progenitor experienced a complex birth environment or disruption history.
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