汤博2：第一个具有显著绝对扩散或嵌入冷恒星流的疏散星团？
Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
摘要：
我们提出了新的丰度和径向速度的恒星领域的疏散星团汤博2，这已被认为是与银河系的Anticenter恒星结构（也被称为麒麟座流）。使用VLT/FLAMES与UVES和GIRAFFE摄谱仪，我们发现一个径向速度（RV）< V_{r} >= 121 \pm 0.4 km/s使用18汤博2星团恒星。我们对RV选择成员的丰度分析发现，汤博2比以前的研究发现的更富含金属;此外，与以前的工作不同，我们更大的样本还揭示了具有星团速度的恒星在化学性质上表现出相对较大的分布（例如，δ [Fe/H] > 0.2）。这是第一次在疏散星团中观察到可能的丰度分布，尽管这是我们观察到的几种可能的解释之一。虽然[α/Fe]与[Fe/H]有明显的趋势，但这些“RV团簇成员”的丰度分布也可能暗示可能分为两个具有不同平均化学特征的主要团簇，即（<[Fe/H]>，<[Ti/Fe]>）~（-0.06，+0.02）和（-0.28，+0.36）。根据位置和运动学，汤博2可能是GASS/麒麟座星团的成员，这使得汤博2成为最初提出的GASS/麒麟座星团家族中的第二个星团。然而，我们探索了其他可能的解释，为观察到的丰度和两个可能的亚种群的传播，最可能的解释是，金属贫（[Fe/H] = -0.28），更集中的人口是真正的汤博2星团恒星和富金属（[Fe/H] = -0.06）星族是一个重叠的、运动学相关的、但“冷”（sigma_V < 2 km/s）的恒星流，其位置在R_{gc} >= 15 kpc。
英文摘要：
We present new abundances and radial velocities for stars in the field of the open cluster Tombaugh 2, which has been suggested to be associated with the Galactic Anticenter Stellar Structure (also known as the Monoceros stream). Using VLT/FLAMES with the UVES and GIRAFFE spectrographs, we find a radial velocity (RV) of <V_{r}> = 121 \pm 0.4 km/s using eighteen Tombaugh 2 cluster stars. Our abundance analysis of RV-selected members finds that Tombaugh 2 is more metal-rich than previous studies have found; moreover, unlike the previous work, our larger sample also reveals that stars with the velocity of the cluster show a relatively large spread in chemical properties (e.g., Delta[Fe/H] > 0.2). This is the first time a possible abundance spread has been observed in an open cluster, though this is one of several possible explanations for our observations. While there is an apparent trend of [alpha/Fe] with [Fe/H], the distribution of abundances of these "RV cluster members" also may hint at a possible division into two primary groups with different mean chemical characteristics -- namely (<[Fe/H]>,<[Ti/Fe]>) ~ (-0.06, +0.02) and (-0.28, +0.36). Based on position and kinematics Tombaugh 2 is a likely member of the GASS/Monoceros stream, which makes Tombaugh 2 the second star cluster within the originally proposed GASS/Monoceros family. However, we explore other possible explanations for the observed spread in abundances and two possible sub-populations, with the most likely explanation being that the metal-poor ([Fe/H] = -0.28), more centrally-concentrated population being the true Tombaugh 2 clusters stars and the metal-rich ([Fe/H] = -0.06) population being an overlapping, and kinematically associated, but "cold" (sigma_V < 2 km/s) stellar stream at R_{gc} >= 15 kpc.
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