Is the Young Star Association ϵ Cha Double?

Abstract

The kinematics of the ϵ Cha young stellar association close to the Sun has been studied based on a list of candidate stars from the Dickson-Vandervelde et al. work. The working sample consists of 26 stars with parallaxes, proper motions from the Gaia DR3 catalog and radial velocities taken from literary sources. The orbits of the stars back to the past were constructed, and the moment when the association had a minimum spatial size was determined, as well as an analysis of the dependencies of the velocities \(U,\;V,\;W\) on the coordinates \(x,\;y,\;z\) was carried out. It is shown that the initial sample is divided into two parts with different kinematic properties. The first sample included 9 stars. Based on the construction of the orbits of these 9 stars, an age estimate of \(t = 4.9 \pm 0.8\) million years was obtained. An expansion coefficient in the \(xz\) plane with the value \({{K}_{{xz}}} = 135 \pm 19\) km/s/kpc was also found for them, on the basis of which another age estimate \(t = 7.2 \pm 1.0\) Ma was obtained. The second sample included 17 stars. The construction of their orbits gave an estimate of age \(t = 0.2 \pm 0.3\) Ma, and based on the gradient \(dW{\text{/}}dz = 707 \pm \) 248 km/s/kpc, a second estimate of their age \(t = 1.4 \pm 0.5\) Ma was obtained. This suggests that the \(\epsilon \) Cha association either consists of two groupings of different ages, or a younger one arose as a result of a recent outbreak of star formation within a common star system. The question of the gravitational connection of the groupings has not been considered in the framework of this work.