Model Atmosphere Analysis of the Weakly Magnetic DZ White Dwarf G165‐7

A reanalysis of the strongly metal-blanketed DZ white dwarf G165-7 ispresented. An improved grid of model atmospheres and synthetic spectra is usedto analyze BVRI, JHK, and ugriz photometric observations as well as a highquality Sloan Digital Sky Survey spectrum covering the energy distribution from3600 to 9000 A. The detection of splitting in several lines of Ca, Na, and Fe,suggesting a magnetic field of Bs~650 kG, is confirmed by spectropolarimetricobservations that reveal as much as +/- 7.5% circular polarization in many ofthe absorption lines, most notably Na, Mg, and Fe. Our combined photometric andspectroscopic fit yields Teff = 6440 K, log g=7.99, log H/He=-3.0 and logCa/He=-8.1. The other heavy elements have solar ratios with respect to calcium,with the exception of Na and Cr that had to be reduced by a factor of two andthree, respectively. A crude polarization model based upon the observed localspectral flux gradient yields a longitudinal field of 165 kG, consistent withthe mean surface field inferred from the Zeeman splitting. The inclusion ofthis weak magnetic field in our synthetic spectrum calculations, even in anapproximate fashion, is shown to improve our fit significantly.Comment: 26 pages, 7 figures, 2 tables, accepted for publication in Ap