Cool metallic-line white dwarfs, radial velocities, and interstellar accretion

Interstellar accretion is observed, and radial velocities from the positions of the H and K lines of Ca II are derived from observations of the spectra of 15 metallic-line white dwarfs. The present and past spatial distribution of the white dwarfs is compared with the distribution of local interstellar matter. Ca accretion from the local interstellar medium cannot proceed at a rate consistent with the observed abundances in cool white dwarfs. The limiting factors are the observed lack of sufficiently dense interstellar matter within 75 pc of the sun, and the low effective temperature of many of the stars. A reasonable alternative to interstellar accretion appears to be accretion of matter in the circumstellar environment.