Temperature fluctuations in interstellar dust grains

Temperature fluctuations in interstellar dust grains caused by absorption of ultraviolet photons are discussed. Temperature probability distributions are presented for various assumptions about the grain specific heat and far infrared emissivity. Grains smaller than or about 0.01 may suffer large temperature fluctuations and would spend most of their time at very low temperatures. The equilibrium temperature is not a good measure for most average temperatures of such grains. It is shown that, although small grains spend only a small fraction of their time at the higher temperatures, the emitted far infrared spectrum is significantly shifted towards shorter wavelengths than predicted for grains assumed to be at the equilibrium temperature.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978.