Exploratory scenarios for the differential nuclear and tidal evolution of TZ Fornacis

TL;DR

This study investigates the nuclear and tidal evolution of the TZ Fornacis binary system, comparing observational data with theoretical models under different initial conditions to understand its orbital and rotational dynamics.

Contribution

It introduces a detailed analysis of the differential stellar and tidal evolution of TZ Fornacis using rotating models and explores the impact of initial eccentricity and friction timescale uncertainties.

Findings

Good agreement between observed and predicted orbital elements.

Initial eccentricity significantly affects the evolution of orbital parameters.

Friction timescale influences the synchronization levels of the components.

Abstract

TZ Fornacis is a double-lined eclipsing binary system with similar masses (2.057$\pm$0.001 and 1.958$\pm$0.001 $M_{\odot}$) but characterized by very different radii (8.28$\pm$0.22 and 3.94$\pm$0.17 $R_{\odot}$). This similarity in terms of mass makes it possible to study the system's differential stellar evolution as well as some aspects of its tidal evolution. With regard to its orbital elements, it was recently confirmed that its orbit is circular with an orbital period of 75.7 days. The less massive component rotates about 17 times faster than the primary one, which is synchronized with the mean orbital angular velocity. Our main objective in this work is to study both the nuclear and the tidal evolution of the system. We explored two scenarios regarding the initial eccentricities: a high one (0.30) and a case of an initial circular orbit. A good agreement has been found between the observational values of the eccentricity, synchronism levels, and orbital period with the values predicted by the integration of the tidal evolution equations. The influence of the friction timescale on the evolution of the orbital elements of TZ For is also studied here. The orbital elements most affected by the uncertainties in the friction timescale are the synchronism levels of the two components. On the other hand, we used the properties of the rotating models generated by the GRANADA code as the initial angular velocities instead of using trial values. In this case, comparisons between the theoretical values of the orbital elements and their observed counterparts also lead to a good interagreement.