From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc
From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc
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DOI：
10.1093/mnras/staa1358
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发表时间：
2020-07-01
影响因子：
4.8
通讯作者：
Xiang, Maosheng
中科院分区：
文献类型：
--
作者：
Coronado, Johanna;Rix, Hans-Walter;Xiang, Maosheng
在同一时间同一地点诞生的恒星应该是由相同元素组成的气体形成的。但大多数恒星随后从它们的出生兄弟姐妹，在轨道和轨道阶段，成为“场星”。在这里，我们探索并提供直接的观测证据，这一过程中的银河系盘，通过量化的概率，恒星之间的轨道相似性意味着不可区分的金属丰度。我们通过恒星在作用角空间中的距离Delta（J，theta）来定义它们之间的轨道相似性，而它们的丰度相似性则简单地用Delta[Fe/H]来定义。分析Gala DR 2和LAMOST的主序星样本，我们发现具有相同金属丰度（Delta[Fe/H] < 0.1）的多余对延伸到Delta（J，theta）中相当大的分离，相当于近1 kpc的距离。我们通过一个模拟样本，从一个光滑的相位混合轨道分布，评估这种效果的意义。通过将这样的星星对分组到由Delta（J，theta）连接的朋友的朋友算法的关联中，我们发现100个单丰度组>= 3（大于或等于20个）成员;这些群--一些群集，一些散布在天空中--比平滑相空间分布所预期的数量级更丰富，这表明我们正在目睹恒星诞生协会的“解体”。
Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming 'field stars'. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Delta(J, theta), and their abundance similarity simply by Delta[Fe/H]. Analysing a sample of main-sequence stars from Gala DR2 and LAMOST, we find an excess of pairs with the same metallicity (Delta[Fe/H] < 0.1) that extends to remarkably large separations in Delta(J, theta) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a friend-of-friends algorithm linked by Delta(J,theta), we find 100s of mono-abundance groups with >= 3 (to greater than or similar to 20) members; these groups - some clusters, some spread across the sky - are over an order-of-magnitude more abundant than expected for a smooth phase-space distribution, suggesting that we are witnessing the `dissolution' of stellar birth associations into the field.