The pre-He white dwarfs in eclipsing binaries – III. WASP 1625−04

Abstract

ABSTRACT 1SWASP J162545.15−043027.9 (WASP 1625−04) has been announced as one of EL CVn candidates showing total primary eclipses and ellipsoidal variations. This paper presents the absolute properties of the binary star, based on our high-resolution spectroscopy conducted from 2015 through 2020. From the spectral analysis, the radial velocities (RVs) for both components were obtained with the effective temperature Teff, 1 = 8990 ± 200 K and the rotational rate $v_1\sin \, i=53\pm 5$ km s−1 for the more massive primary. The RV measurements were analysed with archival WASP photometry. From the modelling we obtained: M1 = 1.745 ± 0.013 M⊙, M2 = 0.187 ± 0.002 M⊙, R1 = 1.626 ± 0.008 M⊙, R2 = 0.290 ± 0.003 M⊙, L1 = 15.5 ± 1.4 L⊙, and L2 = 1.84 ± 0.16 L⊙. In the Hertzsprung–Russell diagram, WASP 1625-04 A lies on the zero-age main sequence and its companion accords well with the helium-core white dwarf models of 0.19 M⊙ in the constant luminosity phase. Our improved results demonstrate that WASP 1625−04 is a typical EL CVn-type binary with a low-mass ratio and M2 combination in the thin-disc population and is the product of the stable, non-conservative mass transfer of the precursor binary.