Kinematic properties of the TW Hya association

TL;DR

This study analyzes the kinematic properties of the TW Hya association, confirming its volume expansion and estimating its dynamical age, while also exploring its rotation parameters with mixed results.

Contribution

First-time graphical estimates of the association's proper rigid-body rotation parameters around galactic axes.

Findings

Confirmed volume expansion with coefficient $K_{xyz}=103 ext{ km s}^{-1} ext{kpc}^{-1}$.

Estimated dynamical age of approximately 9.7 million years.

Rotation parameters are not consistently confirmed across different methods.

Abstract

A kinematic analysis of the young stellar association TWHya has been performed. The components of the displacement matrix in the Ogorodnikov-Milne linear model have been estimated both graphically and by solving the basic kinematic equations. The association's volume expansion with a coefficient of $K_{xyz}=103\pm9$ km s$^{-1}$ kpc$^{-1}$ was confirmed, which yields a dynamical age estimate of $t=9.7 \pm0.8$ Myr. Using the graphical method, estimates of the association's proper rigid-body rotation parameters $\omega$ around the galactic axes x and y have been obtained for the first time, with velocity values in the range of 50-70 km s$^{-1}$ kpc$^{-1}$ and errors in their determination of 14-19 km s$^{-1}$ kpc$^{-1}$. However, these values are not confirmed by another method. For example, when solving kinematic equations only using proper motions, all three components of rigid body rotation do not differ significantly from zero, $(\omega_x,\omega_y,\omega_z)=(4,7,11)\pm(5,5,5)$ km s$^{-1}$ kpc$^{-1}$.