The New Magnetic White Dwarf PG 1031+234: Polarization and Field Structure at More than 500 Million Gauss

Abstract

PG 1031+234 is a newly discovered rotating, magnetic white dwarf. Its optical light is highly polarized, P_max ≈ 6%, V_max ≈ -12%, and strongly modulated on the 3 hr 24 minute rotation period. Optical and UV spectrophotometry reveal a spectrum of diffuse absorption features which match Zeeman calculations of hydrogen in fields 200 - 500×10⁶G. The authors discuss the origin of polarized emission from a cold magnetized plasma and derive the polarization characteristics of the propagation eigenmodes. The results are used to model the polarization behavior of PG 1031+234 using crude approximations to the radiation physics and a straightforward geometric analysis. The observations can be reproduced by a rotating star containing an oblique centered dipole which is punctuated near its magnetic equator by a strong magnetic spot.