Spectroscopic analysis of DA white dwarfs with 3D model atmospheres

Abstract

We present the first grid of mean three-dimensional (3D) spectra for pure-hydrogen (DA) white dwarfs based on 3D model atmospheres. We use CO 5 BOLD radiation-hydrodynamics 3D simulations instead of the mixing-length theory for the treatment of convection. The simulations cover the effective temperature range of 6000 < T eff (K) < 15 000 and the surface gravity range of 7 < log g < 9 where the large majority of DAs with a convective atmosphere are located. We rely on horizontally averaged 3D structures (over constant Rosseland optical depth) to compute 3D spectra. It is demonstrated that our 3D spectra can be smoothly connected to their 1D counterparts at higher and lower T eff where the 3D effects are small. Analytical functions are provided in order to convert spectroscopically determined 1D effective temperatures and surface gravities to 3D atmospheric parameters. We apply our improved models to well studied spectroscopic data sets from the Sloan Digital Sky Survey and the White Dwarf Catalog. We confirm that the so-called high-log g problem is not present when employing 3D spectra and that the issue was caused by inaccuracies in the 1D mixing-length approach. The white dwarfs with a radiative and a convective atmosphere have derived mean masses that are the same within ∼0.01 M , in much better agreement with our understanding of stellar evolution. Furthermore, the 3D atmospheric parameters are in better agreement with independent T eff and log g values from photometric and parallax measurements.

The SDSS spectroscopic catalogue of white dwarf-main-sequence binaries: new identifications from DR 9–12

“…Given that 1D white dwarf model spectra such as those used in this work yield overestimated surface gravity values for white dwarfs of effective temperatures below ∼12 000 K (e.g. Koester et al 2009;Tremblay et al 2011), we apply the 3D corrections of Tremblay et al (2013) to our effective temperature and surface gravity determinations (we apply the 3D corrections to all SDSS WDMS binaries we identified in previous works too, as these corrections were not available at that time). We then interpolate these values in the updated cooling sequences of Bergeron, Wesemael & Beauchamp (1995) and derive white dwarf masses.…”

Detached cataclysmic variables are crossing the orbital period gap

“…1, we show the phase-folded RV curves and corresponding fits for these systems. Table 1 lists the results of these fits and the parameters of the systems, where the WD temperatures and masses are taken from Rebassa-Mansergas et al (2012) and 3D model corrections have been applied for systems with temperatures below 12 000 K (Tremblay et al 2013). SDSS J1452+2045 and SDSS J2208+0037 show no absorption features from the WD in the SDSS spectra, meaning that the masses and temperatures cannot be reliably determined.…”

Dynamical masses of a nova-like variable on the edge of the period gap

“…On the other hand, the mass distribution of isolated WDs peaks at ∼ < 0.6 M (e.g. Koester, Schulz & Weidemann 1979;Bergeron, Saffer & Liebert 1992;Kepler et al 2007;Falcon et al 2010;Tremblay et al 2013).…”