2009ApJ...692..502V

We use the X-ray dust halo of the low-mass X-ray binary 4U 1724-307, located in the globular cluster Terzan 2, to probe the interstellar medium along this line of sight (LOS). The X-ray dust halo arises from X-rays scattering off of interstellar dust grains. Using a low optical depth sight line to determine the Chandra ACIS point-spread function, we extracted the radial profile as a function of energy and used it to determine the H column density (N_H) and cloud location along the LOS for several dust grain models, including the commonly-used models of MRN and WD. The resulting N_H values were used to determine the reddening E(B - V), which was then compared with the average E(B - V) for this sight line found by other workers. We found that for this LOS, only the ZDA BARE-AC-S, BARE-GR-FG, and BARE-GR-S models yield reddenings within 1σ of the literature average.