Dust formation in novae

A rudimentary model for the processes that might control grain formation in nova ejecta is developed which can be used to predict which types of nova are good candidates for dust production and to determine an approximate time scale for the appearance of an observable dust-related IR excess. Observations of Nova FH Ser 1970 are reviewed, and an analytical expression for the time scale for the formation of observable dust in novae is obtained by scaling from the observed time of dust formation in that nova. Characteristics of fast novae which might act to limit grain formation are examined, predicted and observed time scales are compared for several novae, and it is suggested that grain formation could be halted by ionization of the ejecta. Slow to moderate novae with peak luminosities of 30,000 to 50,000 times the solar value are considered as the best candidates for developing circumstellar dust shells.