On the temperature of interstellar grains

Abstract

Cooling of grains by emission due to impurity atoms is evaluated. It is shown that recent estimates of this effect are too high, and consequently, that calculated grain temperatures are too low. At the higher temperatures calculated here, grains cannot retain mantles of solid H₂ in normal interstellar clouds. Because the temperatures calculated are minimum values, which are unlikely to be approached in nature, certainly formation of solid H₂, and probably formation of gaseous H₂ and of ice mantles, are likely to be restricted to dark dust clouds where the radiation field is weak.