Is the young star association e Cha double?

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Abstract

The kinematics of the e Cha young stellar association close to the Sun has been studied based on a list of candidate stars from the Dickson-Vandervelde 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 ± 0.8 million years was obtained. An expansion coefficient in the xz plane with the value Kxz = 135±19 km/s/kpc was also found for them, on the basis of which another age estimate t = 7.2 ± 1.0 million years was obtained. The second sample included 17 stars. The construction of their orbits gave an estimate of age t = 0.2 ± 0.3 million years, and based on the gradient dW/dz = 707 ± 248 km/s/kpc, a second estimate of their age t = 1.4 ± 0.5 million years was obtained. This suggests that the e 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.

About the authors

V. V. Bobylev

Central Astronomical Observatory of the Russian Academy of Sciences

Author for correspondence.
Email: bob-v-vzz@rambler.ru
Russian Federation, Pulkovo

A. T. Bajkova

Central Astronomical Observatory of the Russian Academy of Sciences

Email: bob-v-vzz@rambler.ru
Russian Federation, Pulkovo

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