Studying the Kinematics of the Stellar Association TW Hya from Current Data

Abstract

The kinematics of the young stellar association near the Sun TW Hya is studied. Kinematic estimates of the age of this association were obtained in two ways. The first method—the analysis of stellar trajectories integrated back in time—gave an estimate of the age $$t=4.9\pm 1.2$$ Myr. The second was to analyze the instantaneous velocities of the stars; it showed that there was a volume expansion of the stellar system with the angular velocity coefficient $$K_{xyz}=103\pm 12$$ km s$${}^{-1}$$ kpc$${}^{-1}$$. Based on this effect, the time that passed from the beginning of the expansion of the TW Hya association to the present moment was found, $$t=9.5\pm 1.1$$ Myr. The following principal semi-axes of the residual velocity ellipsoid were determined: $$\sigma_{1,2,3}=(5.25,1.84,0.35)\pm(0.34,0.63,0.26)$$ km s$${}^{-1}$$.