GetGaia 2.0: automatic membership and systemic motions of stellar systems with Gaia
Abstract
We present GetGaia 2.0, a public Python package that retrieves the Gaia data around a stellar system and selects its member stars automatically. The membership is a probabilistic model fitted by expectation maximization that combines the astrometry of every source, with its full covariance, the color-magnitude diagram, the sky distribution and, when available, the line-of-sight velocities, from Gaia or from an external catalog. The local systematic errors of the Gaia reference frame are measured on the quasars of each field. The code returns the systemic proper motion (PM) and parallax with their full covariance, a detection significance, a contamination estimate and the structural parameters of the system. We validate it on synthetic catalogs, where it recovers the members with 90-100 percent purity, and run it on Gaia DR3 for the known dwarf galaxies of the Local Group within 850 kpc and for 95 Galactic globular clusters, in tiers that add one piece of literature information at a time. It measures the systemic PMs of 55 dwarf galaxies and 93 globular clusters at a significance of at least 3σ; 29 of the dwarfs and 86 of the clusters are recovered from their position alone. The dwarfs include every Milky Way satellite within 300 kpc brighter than MV=−5.4, ultra-faint systems down to MV=−0.8, and nine galaxies at 370-820 kpc. The PMs agree with the published values within 0.1 mas/yr for 47 of the dwarfs and for all the clusters (median differences of 0.032 and 0.009 mas/yr), with uncertainties equal to those of dedicated studies, and none deviates by more than 3σ. The Gaia line-of-sight velocities alone give the systemic velocity of 71 clusters, within 1 km/s of spectroscopy. GetGaia 2.0 delivers, without manual intervention, the systemic motions and the members of the stellar systems within the reach of Gaia, and is ready for the forthcoming Gaia data releases.
Related
- Stellar proper motions compared with the plane-of-sky magnetic field
- Classical Cepheids in the Nuclear Stellar Disk: membership via dynamical analysis
- HURACAN: A comparison of stellar and interstellar proper motions inside L1688
- Classical Cepheids in the nuclear stellar disk: Membership via dynamical analysis
- Multi-method approach to membership selection in ultra-faint dwarf galaxies
BibTeX
@misc{pino2026getgaia,
title = {{GetGaia 2.0: automatic membership and systemic motions of stellar systems with Gaia}},
author = {Andrés del Pino},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07227},
eprint = {2611.07227},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07227},
}
RIS
TY - UNPB
TI - GetGaia 2.0: automatic membership and systemic motions of stellar systems with Gaia
AU - Andrés del Pino
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.07227
UR - https://arxiv.org/abs/2611.07227
AB - We present GetGaia 2.0, a public Python package that retrieves the Gaia data around a stellar system and selects its member stars automatically. The membership is a probabilistic model fitted by expectation maximization that combines the astrometry of every source, with its full covariance, the color-magnitude diagram, the sky distribution and, when available, the line-of-sight velocities, from Gaia or from an external catalog. The local systematic errors of the Gaia reference frame are measured on the quasars of each field. The code returns the systemic proper motion (PM) and parallax with their full covariance, a detection significance, a contamination estimate and the structural parameters of the system. We validate it on synthetic catalogs, where it recovers the members with 90-100 percent purity, and run it on Gaia DR3 for the known dwarf galaxies of the Local Group within 850 kpc and for 95 Galactic globular clusters, in tiers that add one piece of literature information at a time. It measures the systemic PMs of 55 dwarf galaxies and 93 globular clusters at a significance of at least 3σ; 29 of the dwarfs and 86 of the clusters are recovered from their position alone. The dwarfs include every Milky Way satellite within 300 kpc brighter than M_V=−5.4, ultra-faint systems down to M_V=−0.8, and nine galaxies at 370-820 kpc. The PMs agree with the published values within 0.1 mas/yr for 47 of the dwarfs and for all the clusters (median differences of 0.032 and 0.009 mas/yr), with uncertainties equal to those of dedicated studies, and none deviates by more than 3σ. The Gaia line-of-sight velocities alone give the systemic velocity of 71 clusters, within 1 km/s of spectroscopy. GetGaia 2.0 delivers, without manual intervention, the systemic motions and the members of the stellar systems within the reach of Gaia, and is ready for the forthcoming Gaia data releases.
ER -