Temperature as a unique predictor of ZZ Ceti variability

Multichannel spectrophotometry of 14 ZZ Ceti variables furnishes energy distributions and colors on various baselines. Their mean temperature is 11,100 K, the edges of the instability strip for DA stars are at 11,700 and 10,700 K, and the mean gravity log g = 8.0. It is noted that the time-averaged energy distributions of the variables are indistinguishable from those of the nonvariable DA's. It is shown that the probable existence of hotter and cooler patches on the surface produces only small distortions of the emergent flux, affecting mainly the estimates of surface gravity. A list of DA's having colors near those of variables is included. Selection procedures for the MCSP observations are described, insofar as they may affect the color distribution of the variables. The accretion theory of Alcock and Illarionov (1980) is used in deriving the probable mass of accreted hydrogen in a variable. In a cooling time of 4 x 10 to the 8th yr, the accreted mass in close to 10 to the -10 solar mass.