Unidentified Interstellar Lines in the Yellow and Red

Abstract

Six unidentified interstellar lines (Table i) are discussed. Following a brief history of previous observations, Tables 2 and 3 give widths and central absorptions of three of the lines. The total intensity of X 6284, which, in the mean, equals the average for the detached lines Di and D2, shows a somewhat stronger correlation with stellar color excess than does the intensity of the D lines. The widths of the unidentified lines, which are rather diffuse and not sharp like the D lines, and other facts make an atomic origin improbable. The lines may be portions of molecular bands, as yet unidentified. Several facts, however, suggest that the lines are produced by small solid particles, per- haps closely related to those that cause space reddening