arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2009.04290astro-ph.GA
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Milky Way球状星团NGC 7099的难以捉摸的潮汐尾

The elusive tidal tails of the Milky Way globular cluster NGC 7099

A. E. Piatti, J. A. Carballo-Bello, M. D. Mora, C. Cenzano, C. Navarrete, M. Catelan

摘要:

利用暗能量照相机(DECam)进行深重力测光,研究了银河系球状星团NGC 7099的潮外特征。我们到达了星团主序星(MS)关闭点以下近6等,这样我们就处理了最合适的候选者,以追踪位于星团潮汐半径之外的任何恒星结构。从逐星红化校正的色星等图(CMD),我们定义了四个相邻的带沿MS,我们建立了各自的恒星密度图,一旦污染的场星被适当地删除。由此产生的场星清理恒星密度图显示了一个短的潮汐尾和一些分散的碎片。当使用浅得多的盖亚DR2数据集和相同的CMD场星清洗程序时,这种潮汐外的功能很难检测到。事实上,通过使用低于星团MS关闭的2.5等作为最暗的界限(G < 20.5等),星团成员被证明分布在星团的潮汐半径内,并且在以星团为中心的半径为3.5度的圆上发现了一些场星密度变化的线索,并且具有与星团星相似的CMD特征。这些恒星的自行分布与星团的自行分布不同,有一些重叠,类似于距离星团中心3.5度以外的恒星。

英文摘要:

We present results on the extra-tidal features of the Milky Way globular cluster NGC 7099, using deep gr photometry obtained with the Dark Energy Camera (DECam). We reached nearly 6 mag below the cluster Main Sequence (MS) turnoff, so that we dealt with the most suitable candidates to trace any stellar structure located beyond the cluster tidal radius. From star-by-star reddening corrected color-magnitude diagrams (CMDs) we defined four adjacent strips along the MS, for which we built the respective stellar density maps, once the contamination by field stars was properly removed. The resulting field star cleaned stellar density maps show a short tidal tail and some scattered debris. Such extra-tidal features are hardly detected when much shallower Gaia DR2 data sets are used and the same CMD field star cleaning procedure is applied. Indeed, by using 2.5 magnitudes below the cluster MS turnoff as the faintest limit (G < 20.5 mag), cluster members turned out to be distributed within the cluster's tidal radius, and some hints for field star density variations are found across a circle of radius 3.5deg centered on the cluster and with similar CMD features as cluster stars. The proper motion distribution of these stars is distinguishable from that of the cluster, with some superposition, which resembles that of stars located beyond 3.5deg from the cluster center.

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