Acoustic fluxes in white dwarfs

Estimates of the acoustic flux generated in white dwarf convection zones are given. Wide ranges of mass, effective temperature, and convective efficiency have been considered. Homogeneous hydrogen- and helium-rich convective envelope models were computed as well as inhomogeneous models representing DA white dwarfs with thin layers of hydrogen surrounding helium-dominated regions. The calculation of the transition zone that separates the hydrogen- and helium-rich layers of these models is extended to take into account the fact that both hydrogen and helium are non-trace species. Only very thin layers of hydrogen are allowed if an underlying helium convection zone is to produce acoustic noise in these inhomogeneous models. It is suggested that such layers are unstable against mixing. Using the input acoustic flux of the homogeneous envelopes, the soft-X-ray luminosities of acoustically heated white dwarf coronae are estimated according to Hearn's coronal model. If such coronae exist, they could be detectable by present day techniques.