# Disentangling the spatial substructure of Cygnus OB2 from Gaia DR2

## TL;DR

This study uses Gaia DR2 parallaxes to reveal complex line-of-sight substructure in Cygnus OB2, identifying multiple stellar groups at different distances and improving understanding of its spatial composition.

## Contribution

The paper introduces a novel approach using a parameterised model and MCMC sampling to analyze Gaia parallaxes, uncovering detailed substructure in Cygnus OB2.

## Key findings

- Main group at ~1760 pc, farther than previous estimates
- Foreground group identified at ~1350 pc
- Method effectively distinguishes multiple stellar populations

## Abstract

For the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parameterised model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax-distance transformation and the asymmetry of the resulting probability distribution. By using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test we identify two different stellar groups superposed on the association. We find the main Cygnus OB2 group at ~1760 pc, further away than recent estimates have envisaged, and a foreground group at ~1350 pc. We also calculate individual membership probabilities and identify outliers as possible non-members of the association.