Maximum rates of period change for DA white dwarf models with carbon and oxygen cores

The maximum rates of the period change for DA white dwarfs expected from theoretical evolutionary models of 0.5 and 0.6 solar-mass DAV stars with carbon and oxygen core compositions suggested by standard evolutionary theory. It is found that, for models near the blue edge of the observed instability strip, the maximum rate of period change can be as high as 7-9 x 10 exp -15 s/s. The present oxygen-core models have values that are about 20 percent larger than that because of their lower heat capacity. In general, the 0.5-solar-mass models have values of the maximum rates of period change that are about 40 percent larger than those of the 0.6 solar-mass models, due to the larger surface area and lower integrated heat capacity of the former.