Distribution of the target stars in longitude vs. distance (top) and latitude vs. distance (middle for b ≥ 70° and bottom for b ≤ 70°). The stars have been divided into two groups, according their latitudes (see text). In the top graph, the two groups of stars are separated by a yellow line, except for the three targets 14 to 16 that are at low longitudes but seem to be located in the direction of the high-latitude arch. The red (resp. black) numbers show the target star without (resp. with) interstellar sodium lines at radial velocities identical to the HI loop I radio velocities. The stars with interstellar lines are also shown with rectangular symbols.