IZ Tel and UW Vir: Southern oscillating eclipsing Algol systems with active mass transfer

TL;DR

This paper presents a detailed analysis of two semi-detached eclipsing binary systems, IZ Tel and UW Vir, revealing active mass transfer, pulsations, and mode coupling in their primary δ Sct stars, based on spectroscopy and photometry.

Contribution

It provides new component masses, pulsation frequencies, and evidence of mode coupling in the primary stars of IZ Tel and UW Vir, expanding understanding of oEA systems.

Findings

Mass transfer confirmed in both systems.

Primary stars are δ Sct pulsators with multiple frequencies.

Mode coupling and amplitude modulations observed over four years.

Abstract

This study is an in-depth examination of IZ Tel and UW Vir which are semi-detached oscillating Eclipsing Algol binary systems (oEA stars). The radial velocities of both components of each system were derived using spectra observed with the Australian National University's 2.3 m telescope. The spectral types of the IZ Tel primary and secondary components were determined as F2V and K2IV; and those of UW Vir were determined as A7V and K6IV, respectively. Spectroscopy revealed mass transfer in progress which was confirmed by the photometric analysis for both cases and also by Eclipse-Timing Variation analysis in the case of UW Vir. Data from the Transiting Exoplanet Survey Satellite (TESS) and ground-based observations enabled detailed light-curve modelling and pulsation analysis. We determined component masses of $M_1=1.48$ M_sun and $M_2=0.33$ M_sun for IZ Tel, and $M_1=2.39$ M_sun and $M_2=0.67$ M_sun for UW Vir from the simultaneous solution of the light and radial velocity curves. Spectra during total eclipses of the primary components revealed H$\alpha$ emission was present. Both primary components are $\delta$ Sct stars. That of IZ Tel pulsates with a dominant frequency of 13.56 d$^{-1}$, which is revealed as non-radial pressure mode, as well as in another 16 combination frequencies. The primary component of UW Vir oscillates in three main frequencies within the range 34.9-43.3 d$^{-1}$ and in more than 50 another combination frequencies. Mode coupling was detected in the three main frequencies, which showed amplitude and phase modulations within a time span of approximately four years. The physical and pulsational properties of the $\delta$ Sct stars of both systems were compared with other members of oEA stars.