# Gaia Parallax of Milky Way Globular Clusters -- A Solution of Mixture Model

## TL;DR

This paper introduces a mixture model method to derive parallaxes of Milky Way globular clusters directly from Gaia data, avoiding membership issues and providing an independent astrometric solution validated with simulations and real data.

## Contribution

The paper presents a novel mixture model approach for globular cluster parallax estimation that bypasses membership determination and offers an independent, validated astrometric measurement method.

## Key findings

- Resolved 120 globular clusters using Gaia DR2 parallaxes.
- Achieved accuracy comparable or better than previous methods.
- Identified a systematic offset in Gaia parallaxes of -27.6 μas.

## Abstract

We have established a mixture model approach to derive the parallax of the Milky Way globular clusters. It avoids the problem of cluster membership determination and provides a completely independent astrometrical solution by purely using the parallax data. This method is validated with simulated clusters of \cite{2017MNRAS.467..412P}. We have resolved 120 real globular clusters by the mixture model using parallaxes of the second data release of \gaia. They construct the largest direct parallax sample up to now. In comparing with other direct parallax results based on cluster members, including 75 clusters of \cite{2018A&A...616A..12G}, our method presents its accuracy, especially for some particular clusters. A systematic offset of $-27.6\pm1.7$ $\mu$as, together with a scatter of $22.8\pm1.3$ $\mu$as is found in comparing with other indirect parallax measurements. They are consistent with the global value and the variation of the zero-point of current \gaia parallaxes. Distances of several specific nearby globular clusters are discussed while the closest ones can reach high precisions, even taking the systematic error into account.