New galactic population class

Abstract

GALACTIC γ rays have been shown to come from regions where H2 is dense, and where also ‘population I’ objects are predominantly found. The existence of such regions can be interpreted using the density-wave model of spiral galaxies, and leads us to propose here a change in the Baade classification scheme: ‘population I’ now to include all the objects associated with the H2 clouds, and a new class, ‘population 0’, to refer to the regions, relatively richer in atomic hydrogen, which lie further from the galactic centre.