Distances to the globular clusters 47 Tucanae and NGC 362 using Gaia DR2 parallaxes

TL;DR

This study uses Gaia DR2 parallaxes and background stars to accurately determine the distances to globular clusters 47 Tucanae and NGC 362, addressing systematics and providing first direct parallax-based measurements.

Contribution

It presents the first precise direct distance measurements to these clusters using Gaia DR2 parallaxes, accounting for parallax systematics and magnitude dependence.

Findings

Distance to 47 Tuc: 4.45 kpc

Distance to NGC 362: 8.54 kpc

First direct parallax-based distances for these clusters

Abstract

Using parallaxes from Gaia DR2, we estimate the distance to the globular clusters 47 Tuc and NGC 362, taking advantage of the background stars in the Small Magellanic Cloud and quasars to account for various parallax systematics. We found the parallax to be dependent on the Gaia DR2 G apparent magnitude for stars with $13<\textrm{G}<18$ , where brighter stars have a lower parallax zero point than fainter stars. The distance to 47 Tuc was found to be $4.45\pm0.01\pm0.12$ kpc, and for NGC 362 $8.54\pm0.20\pm0.44$ kpc with random and systematic errors listed respectively. This is the first time a precise distance measurement directly using parallaxes has been done for either of these two globular clusters.