The Pre-He White Dwarfs in Eclipsing Binaries. IV. WASP 1814+48 with Multiperiodic Pulsations

Abstract

For the EL CVn candidate 1SWASPJ181417.43+481117.0 (WASP 1814+48), we secured the first spectroscopic observations between 2015 April and 2021 March. Using the echelle spectra, the radial velocities (RVs) of the primary star were measured with its atmospheric parameters of $T_{\mathrm{eff},1}=7770\pm 130$ K and $v_1$$\sin$$i=47\pm 6$ km s${}^{-1}$. We fitted our single-lined RVs and the TESS light curve simultaneously. From the binary modeling, we determined the following fundamental parameters for each component: $M_1=1.659\pm 0.048$ $M_{\odot }$, $R_1=1.945\pm 0.027$ $R_{\odot }$, and $L_1=12.35\pm 0.90$ $L_{\odot }$ for WASP 1814+48 A, and $M_2=0.172\pm 0.005$ $M_{\odot }$, $R_2=0.194\pm 0.005$ $R_{\odot }$, and $L_2=0.69\pm 0.07$ $L_{\odot }$ for WASP 1814+48 B. The surface gravity of $\log g_2=5.098\pm 0.026$ obtained from $M_2$ and $R_2$ is concurrent with 5.097$\pm$0.025 computed directly from the observable quantities. WASP 1814+48 B is well-matched with the 0.176 M${}_{\odot }$ white dwarf (WD) evolutionary model for $Z=0.01$. The metallicity and our Galactic kinematics indicate that the program target is a thin-disk star. The whole light residuals after removal of the binary trend were analyzed and found to oscillate at a total of 52 frequencies. Among these, most of the low frequencies below 24 day${}^{-1}$ are aliases and orbital harmonics. The five significant frequencies between 32 and 36 day${}^{-1}$ are the pulsation modes of WASP 1814+48 A located in the $\delta$ Sct domain on ZAMS, and the high frequencies of 128$-$288 day${}^{-1}$ arise from WASP 1814+48 B in the pre-He WD instability strip. Our results reveal that WASP 1814+48 is the fifth EL CVn star that is composed of a $\delta$ Sct-type primary and a pre-ELMV (extremely low-mass pre-He WD variable).

16 pages, including 7 figures and 6 tables, accepted for publication in MNRAS

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