标题： 到仙女座星云的距离 显示英文标题

标题： The Distance to the Draco Cloud

摘要： 对银河系中中间速度和高速气体性质的理解受到个别云团距离估计不足的阻碍。在大卫·邓纳普天文台启动了一个项目，旨在通过沿这些云团视线方向观测早期型恒星并寻找云团系统速度处的钠双线吸收来解决缺乏距离测量的问题。通过光谱视差估计前景恒星（无吸收）和背景恒星（有吸收）的距离，从而估计被限制的云团的距离。在本信中，我们介绍了这个正在进行的项目的第一个结果，即对德拉科云的距离测量，德拉科云是研究最深入的中间速度云之一。这里提供的结果是第一个紧密限制德拉科云位置的距离范围。我们简要描述了目标选择和观测方法，然后展示了对于一颗恒星（TYC~4194~2188）在德拉科云速度处的吸收现象，以及对于其他几颗恒星没有吸收的现象。我们推导出德拉科云的距离范围为463$^{+192}_{-136}$到618$^{+243}_{-174}$光年。 显示英文摘要

摘要： The understanding of the nature of intermediate and high velocity gas in the Milky Way is hampered by a paucity of distance estimates to individual clouds. A project has been started at the David Dunlap Observatory to address this lack of distance measures by observing early-type stars along the line of sight towards these clouds and searching for sodium doublet absorption at the clouds' systemic velocities. Distances to foreground stars (no absorption) and background stars (with absorption) are estimated from spectroscopic parallax, and thus the distance to the bracketed cloud is estimated. In this Letter, we present the first result from this ongoing project, a measurement of the distance to the Draco Cloud, which is the most studied of the intermediate velocity clouds. The result presented here is the first distance bracket which tightly constrains the position of the Draco Cloud. We briefly describe our target selection and observing methodology, and then demonstrate absorption at the velocity of the Draco Cloud for one star (TYC~4194~2188), and a lack of absorption for several other stars. We derive a distance bracket to the Draco Cloud of 463$^{+192}_{-136}$ to 618$^{+243}_{-174}$~pc.