The Pre-He White Dwarfs in Eclipsing Binaries. II. WASP 0843-11

Abstract

We present the Transiting Exoplanet Survey Satellite (TESS) photometry and our high-resolution spectra of the EL CVn-type star 1SWASP J084356.46-113327.5 (WASP 0843-11), which consists of an F-type main-sequence (MS) star and a hotter low-mass helium white dwarf precursor (pre-He WD). In a spectral analysis, double-lined radial velocities (RVs) were obtained for the first time. From a simultaneous analysis of the TESS light and RV curves, the masses, radii, and temperatures of each component were determined to be M₁ = 1.733 ± 0.031 M_⊙, M₂ = 0.220 ± 0.008 M_⊙, R₁ = 2.094 ± 0.013 R_⊙, R₂ = 0.331 ± 0.003 R_⊙, T₁ = 6960 ± 120 K, and T₂ =9870 ± 310 K, respectively. According to their physical properties, the primary and secondary stars are located on the instability strips of δ Sct/γ Dor hybrids and extremely low-mass WDs, respectively. We applied multiple frequency analyses to the residual light curve after subtracting the binarity effects and detected a total of four independent frequencies. A frequency of f₃ = 1.6356 day^-1 in the low-frequency region was reminiscent of γ Dor stars, while the other three frequencies of f₂, f₁₅, and f₁₈ in the high-frequency region (150-196 day^-1) are probably related to pre-He WD components. Our results demonstrate that the more massive MS primary star of WASP 0843-11 is a γ Dor pulsator, whereas the hotter secondary component is a pre-He WD with high-frequency pulsations.