Absolute Properties of the Oscillating Eclipsing Algol X Trianguli

Abstract

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 1sini = 84 ± 6 km s−1 and T eff,1 = 7900 ± 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. The absolute parameters of our target star were accurately and directly determined to be M 1 = 2.137 ± 0.018 M ⊙, M 2 = 1.101 ± 0.010 M ⊙, R 1 = 1.664 ± 0.010 R ⊙, R 2 = 1.972 ± 0.010 R ⊙, L 1 = 9.67 ± 0.55 L ⊙, and L 2 = 2.16 ± 0.09 L ⊙. 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 δ Sct variables. The overall results demonstrate that X Tri is an oEA star system consisting of a δ Sct primary and its lobe-filling companion in the semidetached configuration.