A preliminary comparison of photometric (MWSC) and trigonometric (TGAS) distances of open cluster stars

TL;DR

This study compares photometric and trigonometric distance scales for open cluster stars, finding good overall agreement up to certain distance thresholds, thus validating the consistency of these measurement methods.

Contribution

It provides a comprehensive comparison of MWSC photometric distances with Gaia TGAS parallaxes for over a thousand clusters, highlighting their agreement and limitations.

Findings

Good agreement between distance scales up to 2000 pc

Residuals are small and unbiased within certain distance ranges

Agreement improves for larger, well-populated clusters

Abstract

Our goal was to compare the open cluster photometric distance scale of the global survey of star clusters in the Milky Way (MWSC) with the distances derived from trigonometric parallaxes from the Gaia DR1/TGAS catalogue and to investigate to which degree and extent both scales agree. We compared the parallax-based and photometry-based distances of 5743 cluster stars selected as members of 1118 clusters based on their kinematic and photometric MWSC membership probabilities. We found good overall agreement between trigonometric and photometric distances of open cluster stars. The residuals between them were small and unbiased up to $\log (d,[pc]) \approx 2.8$. If we considered only the most populated clusters and used cluster distances obtained from the mean trigonometric parallax of their MWSC members, the good agreement of the distance scales continued up to $\log (d,[pc]) \approx 3.3$.