The Local Interstellar Ultraviolet Radiation Field

Abstract

I have used the Hipparcos Input Catalogue, together with Kurucz model stellar atmospheres and information on the strength of the interstellar extinction, to create a model of the expected intensity and spectral distribution of the local interstellar ultraviolet radiation field, under various assumptions concerning the albedo a of the interstellar grains. (This ultraviolet radiation field is of particular interest because of the fact that ultraviolet radiation is capable of profoundly affecting the chemistry of the interstellar medium.) By comparing my models with the observations, I am able to conclude that the albedo a of the interstellar grains in the far-ultraviolet is very low, perhaps a=0.1. I also advance arguments that my present determination of this albedo is much more reliable than any of the many previous (and conflicting) ultraviolet interstellar grain albedo determinations. Beyond this, I show that the ultraviolet background radiation that is observed at high Galactic latitudes must be extragalactic in origin, as it cannot be backscatter of the interstellar radiation field.