2026ApJ...996...74M

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 white dwarf (WD) binaries with the stellar evolution code MESA and two types of opacity at low temperatures from Ferguson et al. and Freedman et al. 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. is below that from the opacity of Ferguson et al., and the relation derived from the opacity of Freedman et al. can better explain the observations. In addition, we provided fitting formulae for the relations derived from the opacity of Freedman et al. at different metallicities.