ON THE SPATIAL COINCIDENCE OF HYDROXYL AND METHANOL MASERS

We argue that purely gas-phase chemical models for the production of OH in hydroxyl masers around ultracompact H II regions such as W3(OH) cannot account for the CH3OH in the methanol masers that are found to coincide with the hydroxyl masers in these sources. We suggest that the CH3OH in the masers is injected into the gas phase by evaporation of the grain mantles, the grains being heated by the passage of weak shocks. Gas evaporation also injects H2O into the gas. Photodissociation of H2O, CH3OH and OH occur at similar rates, and substantial abundances of CH3OH and OH coexist.