Abstract
ABSTRACT We use the data from Gaia Early Data Release 3 (EDR3) to study the kinematic properties of Milky Way globular clusters. We measure the mean parallaxes and proper motions (PM) for 170 clusters, determine the PM dispersion profiles for more than 100 clusters, uncover rotation signatures in more than 20 objects, and find evidence for radial or tangential PM anisotropy in a dozen richest clusters. At the same time, we use the selection of cluster members to explore the reliability and limitations of the Gaia catalogue itself. We find that the formal uncertainties on parallax and PM are underestimated by $10{-}20{{\ \rm per\ cent}}$ in dense central regions even for stars that pass numerous quality filters. We explore the spatial covariance function of systematic errors, and determine a lower limit on the uncertainty of average parallaxes and PM at the level 0.01 mas and 0.025 mas yr$^{-1}$ , respectively. Finally, a comparison of mean parallaxes of clusters with distances from various literature sources suggests that the parallaxes for stars with $G>13$ (after applying the zero-point correction suggested by Lindegren et al.) are overestimated by $\sim 0.01\pm 0.003$ mas. Despite these caveats, the quality of Gaia astrometry has been significantly improved in EDR3 and provides valuable insights into the properties of star clusters.
Highlights
The most recent data release (EDR3) from the Gaia mission (Gaia Collaboration 2021) does not provide new data products, but instead improves upon the previous DR2 in various aspects related to the photometric and astrometric catalogues
We re-examined the kinematics of almost all Milky Way globular clusters, derived the mean parallaxes and proper motions (PM), galactic orbits, and analyzed the internal rotation, dispersion and anisotropy profiles of sufficiently rich clusters
While the improvements in precision for mean PM with respect to studies based on DR2 (Gaia Collaboration 2018, Baumgardt et al 2019, Vasiliev 2019b) is substantial, the precision of the phase-space coordinates is typically limited by distance rather than PM uncertainties
Summary
The most recent data release (EDR3) from the Gaia mission (Gaia Collaboration 2021) does not provide new data products, but instead improves upon the previous DR2 in various aspects related to the photometric and astrometric catalogues. Already after DR2, it became possible to measure the mean parallaxes (Chen et al 2018; Shao & Li 2019) and PM of almost all Milky Way globular clusters (Gaia Collaboration 2018; Baumgardt et al 2019; Vasiliev 2019b) and even to study the internal kinematics of many of these systems: sky-plane rotation (Bianchini et al 2018; Vasiliev 2019c; Sollima et al 2019) and PM dispersion and anisotropy (Jindal et al 2019).
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