The rotation and gravitational redshift of white dwarfs

Abstract

Study of 14 hydrogen-line (DA) degenerate stars at coude' dispersion shows that relatively sharp cores can be detected in most at Ha and sometimes at Hfl. These are produced by non-local- thermodynamic equilibrium effects, at effective temperatures from 14,000 to 25,000 K. Eight of the DA's have cores not much broader than expected from the thermal, slit, and instrumental widths. Projected rotational velocities are certainly less than 40 km s ', and possibly less than 20 or even 10 km I Four are appreciably broader, but rotation is still below km i One cool DAs star apparently shows chromospheric emission, possibly caused by convection. The coude' image tube and Image Photon Counting System permit relatively accurate velocity determinations. The sharp cores do not originate in shells. Their mean apparent gravitational redshift is K = +44.6 + 5.7 km 1 (from 13 stars). The mean mass determined from the massradius relation is in the range 0. .75 me. The major implication for stellar evolution is that degenerate stars have low speciflc angnlar momentum. Since they have also lost most of their mass, transport of angular momentum across molecular-weight barriers must be an efficient process. Subject headings: line profiles - relativity - stars: rotation - stars: white dwarfs