Is the young star association ε Cha double?

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Аннотация

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 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 ε 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.

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Авторлар туралы

V. Bobylev

Central Astronomical Observatory of the Russian Academy of Sciences

Хат алмасуға жауапты Автор.
Email: bob-v-vzz@rambler.ru
Ресей, Pulkovo

A. Bajkova

Central Astronomical Observatory of the Russian Academy of Sciences

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

Әдебиет тізімі

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2. Fig. 1. Distribution of the 26 stars of the ε Cha association in projection on the galactic xy plane and their trajectories (a), vertical distribution and their trajectories traced back in time over an interval of 30 Ma (b). The trajectory of the kinematic centre of the association is shown in red

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3. Fig. 2. Deviations from the trajectory of the kinematic centre (parameter q) over an integration interval of 10 Ma for 26 stars of the ε Cha association. The red colour shows the averaged values and the corresponding dispersions

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4. Fig. 3. Dependences of the velocities U (a), V (b), and W (c) on the z coordinate for 26 stars of the ε Cha association

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5. Fig. 4. Vertical distribution of 17 stars with z < -25 pc and their trajectories (a), 9 stars with z > -25 pc and their trajectories (b). The trajectories of the kinematic centres that are calculated from the stars in these samples are shown in green

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6. Fig. 5. Dependences of the velocities U, V, W on the x, y, z coordinates for a sample of 9 stars with z > -25 pc (b)

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7. Fig. 6. Dependences of the velocities U, V, W on the x, y, z coordinates for a sample of 17 stars with z < -25 pc (b)

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8. Fig. 7. Dependence of the q parameter on time for a sample of 9 stars with z > -25 pc, whose orbits are plotted using the kinematic centre calculated for these 9 stars (a), and with the kinematic centre parameters obtained for all 26 stars of the association (b)

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9. Fig. 8. Dependence of the parameter q on the time of a sample of 17 stars with z < -25 pc, whose orbits are plotted using the kinematic centre calculated from these 17 stars (a), and with the kinematic centre parameters obtained for all 26 stars of the association (b)

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