Density Variations over Subparsec Scales in Diffuse Molecular Gas

We present high-resolution observations of interstellar CN, CH, CH^{+},\ion{Ca}{1}, and \ion{Ca}{2} absorption lines toward the multiple star systemsHD206267 and HD217035. Substantial variations in CN absorption are observedamong three sight lines of HD206267, which are separated by distances of order10,000 AU; smaller differences are seen for CH, CH^{+}, and \ion{Ca}{1}. Gasdensities for individual velocity components are inferred from a chemicalmodel, independent of assumptions about cloud shape. While the componentdensities can differ by factors of 5.0 between adjacent sightlines, thedensities are always less than 5000 cm^{-3}. Calculations show that the deriveddensity contrasts are not sensitive to the temperature or reaction rates usedin the chemical model. A large difference in the CH^{+} profiles (a factor of 2in column density) is seen in the lower density gas toward HD217035.Comment: 9 pages, 2 figures. Accepted for publication in ApJ