PREVENTION OF ACCRETION ONTO WHITE-DWARFS BY STELLAR WINDS

There is indirect observational evidence that hot white dwarfs may have weak stellar winds. In this paper, the interaction between such a wind and the flow of ISM material in the gravitational field of the white dwarf is investigated with the aim of finding limits on the mass-loss rate and terminal velocity of winds capable of preventing accretion from the ISM. The limiting cases of no relative motion of the star and the ISM and supersonic relative motion of the star through the ISM are separately investigated. Each case is treated by generalizing models for the interaction between the solar wind and the local ISM to include the effects of gravity. It is found that, for wind velocities expected for radiatively driven winds, mass-loss rates as low as 10(-21) M. yr-1 are sufficient to prevent accretion from the hot phase of the ISM. To prevent accretion during passages through cold clouds, wind mass-loss rates of order 10(-18)-10(-17) M. yr-1 are required. We also suggest that the metal lines seen in some hot DA spectra result from absorption by shocked wind/ISM material.