Constraining Low-Mass White Dwarf Binaries from Ellipsoidal Variations

TL;DR

This paper refines a method to constrain properties of low-mass white dwarf binaries using ellipsoidal variations, improving parameter estimates through Monte Carlo simulations and analyzing a new binary system.

Contribution

It introduces an improved Monte Carlo-based approach for analyzing ellipsoidal variations in white dwarf binaries and applies it to a new system and previous samples.

Findings

Refined constraints on binary system parameters.

Discrepancies suggest errors in surface gravity measurements.

Analysis of SDSS J1054-2121 provides new insights.

Abstract

Stars are stretched by tidal interactions in tight binaries, and changes to their projected areas introduce photometric variations twice per orbit. Hermes et al. (2014, ApJ, 792, 39) utilized measurements of these ellipsoidal variations to constrain the radii of low-mass white dwarfs in eight single-lined spectroscopic binaries. We refine this method here, using Monte Carlo simulations to improve constraints on many orbital and stellar properties of binary systems that exhibit ellipsoidal variations. We analyze the recently discovered tidally distorted white dwarf binary system SDSS J1054-2121 in detail, and also revisit the Hermes et al. (2014) sample. Disagreements in some cases between the observations, ellipsoidal variation model, and Gaia radius constraints suggest that extrinsic errors are present, likely in the surface gravities determined through model atmosphere fits to stellar spectra.