Enigmas from the Sloan Digital Sky Survey DR7 White Dwarf Catalog

摘要

We report results from a continuation of our searches for magnetic white dwarfs paired in a detached binary with a non-degenerate companion, using the Data Release 7 (DR7) of the Sloan Digital Sky Survey. Some 19,712 spectroscopically-identified white dwarfs from the Kleinman et al. paper were examined, including 1,951 white dwarf - M dwarf pairs. The polar (AM Her) system ST LMi in a low state was found but later recognized not to be a detached pair. Our basic result is that the original situation reported 10 years ago is still the case with now very high statistical significance. Detached polar progenitors, apart from Low Accretion Rate Polars (LARPs), are not found. Magnetic white dwarfs likely form from mergers of (nonmagnetic) white dwarfs, while polars and intermediate polars emerge from common envelope evolution as close binaries - either Roche-lobe-filling mass transfer mode or LARPs.