Is the Young Star Association $\epsilon$Cha Double?

Abstract

The kinematics of the $\epsilon$ 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 $t=4.9\pm 0.8$ 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 $t=7.2\pm 1.0$ million years was obtained. The second sample included 17 stars. The construction of their orbits gave an estimate of age $t=0.2\pm 0.3$ million years, and based on the gradient $\partial W/\partial z=707\pm 248$ km/s/kpc, a second estimate of their age $t=1.4\pm 0.5$ million years 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.

arXiv comment14 pages, 8 figures and 2 tables

References in corpus (22)

• Gaia Data Release 2. Summary of the contents and survey properties
• Gaia Data Release 3: Summary of the content and survey properties
• Local Kinematics and the Local Standard of Rest
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• The local surface density of disc matter mapped by Hipparcos
• The Eta Chamaeleontis Cluster: Origin in the Sco-Cen OB Association
• The star formation history of the Sco-Cen association. Coherent star formation patterns in space and time
• The epsilon Chamaeleontis young stellar group and the characterization of sparse stellar clusters
• Significance Mode Analysis (SigMA) for hierarchical structures. An application to the Sco-Cen OB association
• 3D dynamics of the Orion cloud complex -- Discovery of coherent radial gas motions at the 100-pc scale
• A search for new members of the beta Pic, Tuc-Hor and epsilon Cha moving groups in the RAVE database
• Analysis of the Z Distribution of Young Objects in the Galactic Thin Disk
• A Survey for Low-Mass Stars and Brown Dwarfs in the Eta Cha and Eps Cha Young Associations
• Young stars in Epsilon Cha and their disks: disk evolution in sparse associations
• A stellar relic filament in the Orion star forming region
• Proper motions of young stars in Chamaeleon. I. A Virtual Observatory study of spectroscopically confirmed members
• Gaia-based Isochronal, Kinematic, and Spatial Analysis of the $\epsilon$ Cha Association
• Stars and brown dwarfs in the sigma Orionis cluster. IV. IDS/INT and OSIRIS/GTC spectroscopy and Gaia DR2 astrometry
• New low-mass members of Chamaeleon I and $\epsilon$ Cha
• Galactic Rotation Parameters Based on Stars from Activ Star-Forming Regions with Data from the Gaia DR2 Catalogue
• Spectrophotometric properties of pre-main sequence stars: the Epsilon Chamaeleontis cluster
• New binaries in the epsilon Cha association