deletions | additions       diff --git a/section_Introduction_High_velocity_clouds__.tex b/section_Introduction_High_velocity_clouds__.tex  index 15f8b07..7b73bd0 100644  --- a/section_Introduction_High_velocity_clouds__.tex  +++ b/section_Introduction_High_velocity_clouds__.tex 
...
One major issue in gaining a better physical understanding these enigmatic clouds is their distance. Since there are no objects of standard luminosity in these clouds, there are effectively no distance constraints from HI emission or optical and UV absorption lines, which probe only the distance-independent column densities. Distance not only gives us a mass for these structures, but also a context; the relationship between the cloud and the disk gives us insight as to its origin.  There are a number of indirect methods for measuring the distance to an HVC complex, including H$\alpha$ emission and kinematic structure \cite{Putman_2003, Peek_2007}, but the only proven direct distance measure is stellar absorption. By observing standard candle stars at high spectral resolution, one can look for absorption lines in Na I, Ca II H & K, Ti II, and numerous ultraviolet absorption lines at the velocity of HI emission from HVCs  \cite{1995A&A...302..364S}. By finding detections and non-detections of these absorption lines along lines of sight toward HI emitting HVCs distances can be robustly measured. In this work we report the first upper limit on complex WD using absorption line spectroscopy toward a blue horizontal branch star. We extend the methods of \cite{Sirko_2004} to find the spectral type of a blue horizontal branch star.