Orbital motions and light curves of young binaries XZ Tau and VY Tau

TL;DR

This study presents speckle interferometric observations of young binary stars VY Tau and XZ Tau, revealing their orbital parameters, brightness variations, and flare activity, providing new insights into their dynamic behavior and evolution.

Contribution

First-time determination of the relative displacement and preliminary orbit of VY Tau, and analysis of brightness and flare activity in both binaries.

Findings

XZ Tau's orbit is non-circular and inclined, affecting jet orientation.

Brightness of XZ Tau increased then decreased over the last century, peaking near periastron.

VY Tau's flare activity resumed after 40 years, linked to component A.

Abstract

The results of our speckle interferometric observations of young binaries VY Tau and XZ Tau are presented. For the first time, we found a relative displacement of VY Tau components as well as a preliminary orbit for XZ Tau. It appeared that the orbit is appreciably non-circular and is inclined by $i \lesssim 47^o$ from the plane of the sky. It means that the rotation axis of XZ Tau A and the axis of its jet are significantly non-perpendicular to the orbital plane. We found that the average brightness of XZ Tau had been increasing from the beginning of the last century up to the mid-thirties and then it decreased by $\Delta B > 2$ mag. The maximal brightness has been reached significantly later on the time of periastron passage. The total brightness of XZ Tau's components varied in a non-regular way from 1970 to 1985 when eruptions of hot gas from XZ Tau A presumably had occurred. In the early nineties the variations became regular following which a chaotic variability had renewed. We also report that a flare activity of VY Tau has resumed after 40 yr pause, parameters of the previous and new flares are similar, and the flares are related with the A component.