Profile of the Unidentified Interstellar Absorption Band at 4430 Å at Different Galactic Longitudes

Abstract

THE cause of the diffuse interstellar absorption band centred on 4430 Å is still unknown, thirty years after the recognition of the band's interstellar nature. Because this band, together with other similar bands, can absorb as much visible energy from the radiation of distant stars as is absorbed by the visible Balmer lines, an identification is of obvious interest, and such identification may be critically dependent on a knowledge of the profile of the band. Investigation of the profile is made difficult by its great width and usually small depth. Wilson¹, Wampler² and Herbig³ have produced profiles of 4430 Å in the distant B-star H.D. 183143; these profiles resemble each other at the centre but differ further out in that Wilson finds shallow wings of perhaps even 150 Å width, whereas the overall extents in the other two cases are about 40 Å and 60 Å, the shallow wings being absent.