修整Willman 1 dSph
Trimming Down the Willman 1 dSph
摘要：
威尔曼1（Willman 1）是斯隆数字巡天发现的一个小的低表面亮度天体，暂时被归类为一个非常低光度的dSph星系。进一步的研究支持了这一分类，同时暗示它可能正在经历银河系潜力的破坏。为了更好地限制Willman 1的性质，我们对以过密度为中心的0.6平方度区域中最亮的恒星进行了全面的分析。两颗先前确认的Willman 1 RGB星的高分辨率HET光谱显示，一颗是富金属前景矮星，而另一颗是贫金属巨星。我们确认的一颗RGB恒星是Willman 1的成员，它的金属丰度很低（[Fe/H]=-2.2），α元素丰度也很低（[alpha/Fe]=-0.11）。Washington+ DDO 51测光表明，在先前的研究中发现的7颗最亮的威尔曼1恒星中，有2-5颗实际上是矮星，包括一些金属含量更高的恒星，这些恒星被用来证明丰度分布和比类似光度的星系更富含金属的恒星星族。其余的恒星太蓝或太暗，无法进行光度分类。Washington+ DDO 51测光在视野中识别出三颗潜在的RGB星，但HET光谱显示它们是背景晕星。时间序列测光在视野中识别出一颗明显的变星，但它不太可能与威尔曼1号有关。我们的宽视场调查表明，在超过0.6平方度的范围内，威尔曼1号没有一颗RR型天琴座恒星，一颗BHB型恒星或一颗RGB型恒星超出其潮汐半径。虽然我们的研究结果证实，威尔曼1是最有可能是一个低光度的贫金属dSph星系，它仍然是一个潮汐破坏的贫金属球状星团的可能性。
英文摘要：
Willman 1 is a small low surface-brightness object identified in the Sloan Digital Sky Survey and tentatively classified as a very low luminosity dSph galaxy. Further study has supported this classification while hinting that it may be undergoing disruption by the Milky Way potential. In an effort to better constrain the nature of Willman 1, we present a comprehensive analysis of the brightest stars in a 0.6 square degree field centered on the overdensity. High-resolution HET spectra of two previously identified Willman 1 RGB stars show that one is a metal-rich foreground dwarf while the other is a metal-poor giant. The one RGB star that we confirm as a member of Willman 1 has a low metallicity ([Fe/H]=-2.2) and a surprisingly low alpha-element abundance ([alpha/Fe]=-0.11). Washington+DDO51 photometry indicates that 2-5 of the seven brightest Willman 1 stars identified in previous studies are actually dwarf stars, including some of the more metal-rich stars that have been used to argue both for an abundance spread and a more metal-rich stellar population than galaxies of similar luminosity. The remaining stars are too blue or too faint for photometric classification. The Washington+DDO51 photometry identifies three potential RGB stars in the field but HET spectra show that they are background halo stars. Time series photometry identifies one apparent variable star in the field, but it is unlikely to be associated with Willman 1. Our wide-field survey indicates that over 0.6 square degrees, Willman 1 does not have a single RR Lyrae star, a single BHB star or a single RGB star beyond its tidal radius. While our results confirm that Willman 1 is most likely a low-luminosity metal-poor dSph galaxy, the possibility remains that it is a tidally disrupted metal-poor globular cluster.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
