The relation between helium white dwarf mass and orbital period under two types of opacity

TL;DR

This study models helium white dwarf binary evolution considering different low-temperature opacities, revealing that Freedman et al.'s opacity better matches observations and providing new fitting formulas for various metallicities.

Contribution

It introduces the impact of different low-temperature opacities on the He WD mass-orbital period relation, improving agreement with observational data.

Findings

Freeman et al.'s opacity yields a relation below Ferguson et al.'s.

Freeman et al.'s opacity better explains observed data.

Provided fitting formulas for different metallicities.

Abstract

Helium white dwarfs (He WDs) are end products of low-mass red giant donors in close binary systems via stable mass transfer or common envelope evolution. At the end of stable mass transfer, there is a well-known relation between the He WD mass and orbital period. Although this relation has been widely investigated, the influence of different types of opacity at low temperatures is ignored. In this work, we modeled the evolution of WD binaries with stellar evolution code MESA and two types of opacity at low temperatures from Ferguson et al. (2005) and Freedman et al. (2008, 2014). We investigated the relation between the WD mass and orbital period and compared these results with observations. We find that the relation derived from the opacity of Freedman et al. (2008, 2014) is below that from the opacity of Ferguson et al. (2005) and the relation derived from the opacity of Freedman et al. (2008, 2014) can better explain the observations. In addition, we provided fitting formulae for the relations derived from the opacity of Freedman et al. (2008,2014) at different metallicities.