3D Model Atmospheres for Extremely Low-Mass White Dwarfs

TL;DR

This paper provides an extensive grid of 3D atmospheric models for low-mass hydrogen-atmosphere white dwarfs, improving the accuracy of spectroscopic parameter determinations and resolving previous discrepancies in mass and radius measurements.

Contribution

It introduces new 3D model spectra and correction functions for low-mass white dwarfs, enhancing the precision of spectroscopic analyses and revising the ZZ Ceti instability strip boundaries.

Findings

3D models significantly reduce surface gravity estimates for low-mass WDs.

Revised models resolve previous mass and radius discrepancies in ELM WDs.

Updated instability strip boundaries include new ELM pulsators.

Abstract

We present an extended grid of mean three-dimensional (3D) spectra for low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD radiation-hydrodynamics 3D simulations covering Teff = 6000-11,500 K and logg = 5-6.5 (cgs units) to derive analytical functions to convert spectroscopically determined 1D temperatures and surface gravities to 3D atmospheric parameters. Along with the previously published 3D models, the 1D to 3D corrections are now available for essentially all known convective DA WDs (i.e., logg = 5-9). For low-mass WDs, the correction in temperature is relatively small (a few per cent at the most), but the surface gravities measured from the 3D models are lower by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the discrepancies seen in the radius and mass measurements for relatively cool ELM WDs in eclipsing double WD and WD + milli-second pulsar binary systems. We also use the 3D corrections to revise the boundaries of the ZZ Ceti instability strip, including the recently found ELM pulsators.