Distances to the Globular Clusters 47 Tucanae and NGC 362 Using Gaia DR2 Parallaxes

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-band apparent magnitude for stars with 13 < 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 ± 0.01 ± 0.12 kpc, and for NGC 362 8.54 ± 0.20 ± 0.44 kpc with random and systematic errors listed respectively. This is the first time a precise distance measurement directly using parallaxes has been determined for either of these two globular clusters.

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

“…Using Gaia parallaxes, Chen et al (2018) obtained a distance of 4.45 kpc ± 0.01 (random) ± 0.12 (systematic) to 47 Tuc (we note that the recent paper by Shao & Li (2019) has not improved on their results).…”

Gaia parallax of Milky Way globular clusters – A solution of mixture model

“…Definitely, the offset is in good agreement with the global zero-point of ∼ −29 µas, though it was reported that this value changes with different tracers (Arenou et al 2018). The Chen et al (2018) and the blue quadrangle is from Brown et al (2018). Light grey shadow shows the scatter (1σ range) centered on the average value of ∆ c , while the narrower grey shadow has the same meaning but exclude M 62(NGC 6266) (see table 2 for these values).…”

“…Gaia Collaboration et al (2018) (hereafter H18) obtained the parallaxes ( c ) of 75 GCs (∼half of the known Milky Way GCs) and used them as a tracer to discuss the zero-point and the calibration noise of Gaia parallax. Chen et al (2018) determined the absolute Gaia parallax of two specific GCs (47 Tuc and NGC 362) based on their relative parallaxes to the Small Magellanic Cloud (SMC).…”

Using Gaia DR2 to detect extratidal structures around the Galactic globular cluster NGC 362

“…The saturation level considered to generate the map contained in Figure 2 is S = 5. We also computed the orbit for NGC 362 using the Miyamoto & Nagai (1975) potentials based on the proper motions derived by Gaia Collaboration (2018a), a radial velocity of v r = 223.5 km s −1 , the heliocentric distance derived by Chen et al (2018), a circular speed of V c (R ) = 220 km s −1 , and the Solar motion from Schönrich et al (2010). The inmediate orbit of NGC 362, integrated backwards and forwards, is finally overplotted in the map.…”

“…One of the objectives of this work is to evaluate whether this technique is adequate for data with the current quality of the information contained in the Gaia DR2 or it will be (only) possible to identify extratidal features in nearby GCs using the end-of-mission data release. Among the nearby Galactic GCs, we focus on NGC 362, a system at R = 8.5 kpc (Chen et al 2018) with coordinates (α, δ)=(15.8099 • ,-70.8489 • ) (Gaia Collaboration 2018a). This cluster is an ideal target to test the method proposed in this Paper because i) it is close enough to have a decent number of main-sequence (MS) stars observed below its Turn-Off (TO), ii) its population is likely contaminated by Small Magellanic Cloud (SMC) stars, and iii) a remarkable GC, NGC 104 (47 Tucanae), is located at only a few degrees away and it may also contribute stars in the field around NGC 362.…”