Gaia EDR3 confirms that Westerlund 1 is closer and older than previously thought

TL;DR

Gaia EDR3 data confirms Westerlund 1 is closer and older than previously thought, with improved individual star parallax precision but similar cluster uncertainty, indicating systematic limitations.

Contribution

This study provides a refined distance and age estimate for Westerlund 1 using Gaia EDR3 parallaxes and Bayesian inference, confirming its closer and older status.

Findings

Westerlund 1 is approximately 2.8 kpc away.

Individual star parallax uncertainties decreased by 30%.

Cluster parallax uncertainty remains dominated by systematics.

Abstract

Using {\it Gaia} Early Data Release 3 (EDR3) parallaxes and Bayesian inference, we infer a parallax of the Westerlund 1 (Wd1) cluster. We find a parallax of $0.34\pm{0.05}$ mas corresponding to a distance of $2.8^{+0.7}_{-0.6}$ kpc. The new {\it Gaia} EDR3 distance is consistent with our previous result using {\it Gaia} DR2 parallaxes. This confirms that Wd1 is less massive and older than previously assumed. Compared to DR2, the EDR3 individual parallax uncertainties for each star decreased by 30\%. However, the aggregate parallax uncertainty for the cluster remained the same. This suggests that the uncertainty is dominated by systematics, which is possibly due to crowding, motions within the cluster, or motions due to binary orbits.