2005ApJ...620L..39P

Current measurements indicate that the deuterium abundance in diffuse interstellar gas varies spatially by a factor of ∼4 among sight lines extending beyond the Local Bubble. One plausible explanation for the scatter is the variable depletion of D onto dust grains. To test this scenario, we have obtained high signal-to-noise, high- resolution profiles of the refractory ion Ti II along seven Galactic sight lines with D/H ranging from 0.65 to 2.1x10^–5. These measurements, acquired with the recently upgraded Keck/HIRES spectrometer, indicate a correlation between Ti/H and D/H at the better than 95% confidence level Therefore, our observations support the interpretation that D/H scatter is associated with differential depletion. We note, however, that Ti/H values taken from the literature do not uniformly show the correlation. Finally, we identify significant component-to-component variations in the depletion levels among individual sight lines and discuss complications arising from this behavior.: