Gaia EDR3 Confirms that Westerlund 1 is Closer and Older than Previously Thought

Abstract

Abstract Using 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 ± 0.05 mas corresponding to a distance of 2.8 − 0.6 + 0.7 kpc. The new Gaia EDR3 distance is consistent with our previous result using Gaia Data Release 2 (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.