Absolute Properties of the Oscillating Eclipsing Algol X Trianguli

We report results from the TESS photometric data and new high-resolution spectra of the Algol system X Tri showing short-period pulsations. From the echelle spectra, the radial velocities of the eclipsing pair were measured, and the rotational rate and effective temperature of the primary star were obtained to be $v_1$$\sin$$i=84\pm6$ km s$^{-1}$ and $T_{\rm eff,1}=7900 \pm 110$ K, respectively. The synthetic modeling of these observations implies that X Tri is in synchronous rotation and is physically linked to a visual companion TIC 28391715 at a separation of about 6.5 arcsec. The absolute parameters of our target star were accurately and directly determined to be $M_1 = 2.137 \pm 0.018$ $M_\odot$, $M_2 = 1.101 \pm 0.010$ $M_\odot$, $R_1 = 1.664 \pm 0.010$ $R_\odot$, $R_2 = 1.972 \pm 0.010$ $R_\odot$, $L_1 = 9.67 \pm 0.55$ $L_\odot$, and $L_2 = 2.16 \pm 0.09$ $L_\odot$. The phase-binned mean light curve was used to remove the binary effect from the observed TESS data. Multifrequency analysis of the residuals revealed 16 significant frequencies, of which the high-frequency signals between 37 day$^{-1}$ and 48 day$^{-1}$ can be considered probable pulsation modes. Their oscillation periods of 0.021$-$0.027 days and pulsation constants of 0.014$-$0.018 days are typical values of $\delta$ Sct variables. The overall results demonstrate that X Tri is an oEA star system, consisting of a $\delta$ Sct primary and its lobe-filling companion in the semi-detached configuration.