Predicting Gaia's Parallax Distance to the Cygnus OB2 Association with Eclipsing Binaries

TL;DR

This study refines the distance to the Cygnus OB2 Association using eclipsing binaries, achieving a more accurate measurement that aligns with other methods and enhances understanding of star formation in the region.

Contribution

The paper provides new, precise distance measurements to key eclipsing binaries in Cygnus OB2, improving the accuracy of the association's distance estimate and identifying a new member.

Findings

Distance to Cygnus OB2 is approximately 1.33 kpc.

The measured distances agree with previous spectrophotometric and parallax estimates.

Identification of Schulte 3C as a new association member.

Abstract

The Cygnus OB2 Association is one of the nearest and largest collections of massive stars in the Galaxy. Situated at the heart of the "Cygnus X" complex of star-forming regions and molecular clouds, its distance has proven elusive owing to the ambiguous nature of kinematic distances along this $\ell\simeq80$ degree sightline and the heavy, patchy extinction. In an effort to refine the three-dimensional geometry of key Cygnus~X constituents, we have measured distances to four eclipsing double-lined OB-type spectroscopic binaries that are probable members of Cyg~OB2. We find distances of $1.33\pm0.17$, $1.32\pm0.07$, $1.44\pm0.18$, and $1.32\pm0.13$ kpc toward MT91~372, MT91~696, CPR2002~A36, and Schulte~3 respectively. We adopt a weighted average distance of 1.33$\pm$0.06~kpc. This agrees well with spectrophotometric estimates for the Association as a whole and with parallax measurements of protostellar masers in the surrounding interstellar clouds, thereby linking the ongoing star formation in these clouds with Cyg~OB2. We also identify Schulte 3C (O9.5V), a 4" visual companion to the 4.75 day binary Schulte~3(A+B), as a previously unrecognized Association member.