arXiv subjects
Publications and source records attributed to A. Attard.
We present distance estimates to a set of high-latitude intermediate-velocity HI clouds. We explore some of the physical parameters that can be determined from these results, such as cloud mass, infall velocity and height above the Galactic plane. We also briefly describe some astrophysical applications of these data and explore future work.
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.