Hercules dSph的深部LBT成像研究
The Elongated Structure of the Hercules dSph from Deep LBT Imaging
摘要：
我们提出了一个深，宽视场测光调查新发现的武仙座矮球状星系，从大双筒望远镜的数据的基础上。B、V和r中的图像是用大双目照相机获得的，该照相机覆盖23'× 23'视场，幅值为~25.5（5 sigma）。这使得色彩星等图的构建达到了武仙座主序星关闭点以下约1.5等。三滤光片测光使我们能够优先选择可能的武仙座成员星，并在以前未达到的水平上检查这个系统的结构。我们发现武仙座矮星是高度拉长的（3：1），比银河系的任何其他dSph卫星都要长得多，除了破坏人马座矮星。虽然我们不能排除这种不寻常的结构是武仙座作为一个平衡系统所固有的，但我们的研究结果表明，潮汐破裂可能是这种高度椭圆结构的原因。考虑到这个系统相对较大的银河系中心距离（132 +/- 12 kpc），潮汐破坏的迹象将需要武仙座矮星在银河系周围的高度偏心轨道上。
英文摘要：
We present a deep, wide-field photometric survey of the newly-discovered Hercules dwarf spheroidal galaxy, based on data from the Large Binocular Telescope. Images in B, V and r were obtained with the Large Binocular Camera covering a 23' times 23' field of view to a magnitude of ~25.5 (5 sigma). This permitted the construction of colour-magnitude diagrams that reach approximately 1.5 magnitudes below the Hercules main sequence turnoff. Three-filter photometry allowed us to preferentially select probable Hercules member stars, and examine the structure of this system at a previously unattained level. We find that the Hercules dwarf is highly elongated (3:1), considerably more so than any other dSph satellite of the Milky Way except the disrupting Sagittarius dwarf. While we cannot rule out that the unusual structure is intrinsic to Hercules as an equilibrium system, our results suggest tidal disruption as a likely cause of this highly elliptical structure. Given the relatively large Galactocentric distance of this system (132 +/- 12 kpc), signs of tidal disruption would require the Hercules dwarf to be on a highly eccentric orbit around the Milky Way.
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