Distance and Kinematics of the TW Hydrae Association from Parallaxes

TL;DR

This study measures parallaxes and proper motions of TW Hydrae Association members, revealing their space motions, ages, and suggesting they formed from an extended molecular cloud rather than a single event.

Contribution

The paper provides new parallactic distances and kinematic data for 14 members, clarifying their association membership and age distribution.

Findings

Most stars have parallel space motions indicating common origin.

Median age of the stars is approximately 10 million years.

TWA 9 and 22 are not members based on their motions.

Abstract

From common proper motion and signatures of youth, researchers have identified about 30 members of a putative TW Hydrae Association. Only four of these had parallactic distances from Hipparcos. We have measured parallaxes and proper motions for 14 primary members. We combine these with literature values of radial velocities to show that the Galactic space motions of the stars, with the exception of TWA 9 and 22, are parallel and do not indicate convergence at a common formation point sometime in the last few million years. The space motions of TWA 9 and 22 do not agree with the others and indicate that they are not TWA members. The median parallax is 18 mas or 56 pc. We further analyze the stars' absolute magnitudes on pre-main sequence evolutionary tracks and find a range of ages with a median of 10.1 Myr and no correlation between age and Galactic location. The TWA stars may have formed from an extended and filamentary molecular cloud but are not necessarily precisely coeval.