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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  M 1  = 1.733 ± 0.031  M ⊙ ,  M 2  = 0.220 ± 0.008  M ⊙ ,  R 1  = 2.094 ± 0.013  R ⊙ ,  R 2  = 0.331 ± 0.003  R ⊙ ,  T 1  = 6960 ± 120 K, and  T 2  =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  f 3  = 1.6356 day −1  in the low-frequency region was reminiscent of  γ  Dor stars, while the other three frequencies of  f 2 ,  f 15 , and  f 18  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.

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