Maser emissions from comets

Abstract

The 18-cm lines of the OH radical are the only well-documented masers in comets. They have been observed in more than 65 comets since 1973. The good knowledge of their excitation mechanisms and their linear regime allow us to estimate the water production rate and its variation with heliocentric distance from radio observations of OH in comets. Two bright comets, C/1996 B2 (Hyakutake) and C/1995 01 (Hale-Bopp), recently passed perihelion. We give an account of their observing campaigns and of the new insights they provide in the physics of comets. We also discuss the possibility of masering emission for other cometary molecules: H2O, CH, CH3OH.