Surveying DC White Dwarfs for Magnetic Fields

Abstract

A survey of 52 DC white dwarf stars was conducted in circular spectropolarimetry to search for magnetic fields ≳30 kG. Four DC stars were discovered with magnetic fields above 30 kG: G111-49 with Be ~ -220 MG, G183-35 with Be = +6.8 ± 0.5 MG, G256-7 with Be = +4.9 ± 0.5 MG, and G234-4 with Be = +39.6 ± 11.6 kG. A new magnetic DB white dwarf was also discovered, LB 8827 with Be = 1.0 ± 0.5 MG. A total of 15% of the white dwarfs in the survey have a magnetic field >30 kG. This value is far larger than the 2% of DA stars, but more than half of the DC stars were originally misclassified. Only 5% of the reclassified DC stars have magnetic fields above 30 kG. Non-white dwarfs were also observed: the two BL Lacs are unpolarized in circular polarization and an extreme carbon star was discovered.