Measuring M Dwarf Winds with DAZ White Dwarfs

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, showevidence for ongoing accretion of material onto their surfaces. Some DAZs areknown to have unresolved M dwarf companions, which could account for theobserved accretion through a stellar wind. I combine observed Ca abundances ofthe DAZs with information on the orbital separation of their M dwarf companionsto infer the mass loss rate of the M dwarfs. I find that for three of the sixknown DAZs with M dwarf companions, a stellar wind can plausibly explain theobserved accretion on the white dwarfs assuming Bondi-Hoyle accretion of solarabundance stellar winds on the order of 10$^{-14}-10^{-16}\Msun$ yr$^{-1}$. Therest of the sample have companions with orbits $\gtorder$ 1~AU, and requirecompanion mass loss rates of $> 10^{-11}\Msun$ yr$^{-1}$. I conclude that theremust be an alternative explanation for accretion of material onto DAZs withwidely separated companions. The inferred winds for two of the close binariesare orders of magnitude smaller than typically assumed for the angular momentumloss of red dwarf-white dwarf pairs due to magnetic braking from a stellar windand may seriously affect predictions for the formation rate of CVs with lowmass companions.Comment: 18 pages, 3 figures, accepted to Ap