1996PASP..108...92U

In the case of 5 O stars out of 14, the average difference between the line-of-sight velocity component shown by the diffuse interstellar bands (DIBs) and that shown by the interstellar Na I lines exceeds the range ± 10 km s ^-1. For 9 O stars this difference lies in the range ± 6 km s^-1. What does this mean? Because the typical standard deviation of v_DIB from three DIBs is 3.8 ± 1.2 km s^-1 while that of v_NaI from two interstellar lines is 1.8 ± 1.3 km s^-1, the larger values of v_DIB - v_NaI are meaningful. They imply that the grains or molecules carrying the DIBs move with the interstellar Na atoms along the lines of sight to only some O stars.