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

Abstract

A reanalysis of the strongly metal-blanketed DZ white dwarf G165-7 is presented. An improved grid of model atmospheres and synthetic spectra is used to analyze BVRI, JHK, and ugriz photometric observations as well as a highquality Sloan Digital Sky Survey spectrum covering the energy distribution from 3600 to 9000 8. The detection of splitting in several lines of Ca, Na, and Fe, suggesting a magnetic field of B s $ 650 kG, is confirmed by spectropolarimetric observations that reveal as much as AE7.5% circular polarization in many of the absorption lines, most notably Na, Mg, and Fe. Our combined photometric and spectroscopic fit yields T eA ¼ 6440 K, log g ¼ 7:99, log ( H/He) ¼ À3:0, and log (Ca / He) ¼ À8:1. The other heavy elements have solar ratios with respect to Ca, with the exception of Na and Cr, which had to be reduced by a factor of 2 and 3, respectively. A crude polarization model based on the observed local spectral flux gradient yields a longitudinal field of 165 kG, consistent with the mean surface field inferred from the Zeeman splitting. The inclusion of this weak magnetic field in our synthetic spectrum calculations, even in an approximate fashion, is shown to improve our fit significantly.

Excitation and deexcitation processes in atom-Rydberg atom collisions in helium-rich white dwarf atmospheres

“…For instance, an entire array of white dwarfs of other types, as described in Wegner & Koester (1985), Dufour et al (2006Dufour et al ( , 2007, have similar parameters. Consequently, processes (1) and (2) must be just as important as the concurrent processes (3).…”

Merging binary stars and the magnetic white dwarfs

“…Known HFMWDs with poloidal field strength B pol 10 5 G. In the comparison with our models we exclude five of these white dwarfs with B pol < 1 MG (nos 1, 3, 18, 20 and 32) and two more of extremely low mass (nos 19 and 29) that cannot be formed within the bse formulism. References: (1) Valyavin et al (2005); (2) Bergeron, Ruiz & Leggett (2001); (3) Bergeron, Ruiz & Leggett (1992); (4) Vennes et al (2003); (5) Angel (1978); (6) Dufour et al (2005); (7) Pragal & Bues (1989); (8) Putney & Jordan (1995); (9) Schmidt, Stockman, Smith (1992); (10) Giovannini et al (1998); (11) Ferrario et al (1998); (12) Vanlandingham et al (2005); (13) Angel (1977); (14) Angel, Illing & Landstreet (1972); (15) Dobbie et al (2012); (16) Glenn et al (1994); (17) Liebert et al (1993); (18) Bergeron, Ruiz & Leggett (1997); (19) Liebert, Bergeron & Holberg (2003); (20) Girven et al (2010); (21) Dufour et al (2006); (22) Bergeron, Ruiz & Leggett (1993); ...…”

Photometric Variability in a Warm, Strongly Magnetic Dq White Dwarf, SDSS J103655.39+652252.2

“…Line profile calculations including the PB effect have been recently incorporated in stellar models only for a few sensitive lines in Ap stars (Fe ii multiplet Magnetic fields strong enough to push the lines into the PB regime are commonly found in WD stars (see the latest review by Jordan 2009 and references therein), yet since the vast majority of known magnetic WD stars only show hydrogen line splitting, only hydrogen-rich magnetic model atmospheres have been developed in detail to this date. However, the population of magnetic WDs with heavy element features is growing rapidly thanks to the work on DQ (see Schmidt et al 1995), hot DQ (Dufour et al 2009b) and DZ WDs (i.e., LHS 2534 and G165−7; Reid et al 2001;Dufour et al 2006). Accurate determination of the atmospheric parameters for such stars requires the development of a new generation of magnetic model atmospheres that include various field geometries, radiative transfer for all Stokes components, as well as splitting in the PB regime.…”