Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region

TL;DR

This study uses VLBI observations of masers to accurately measure distances and motions of star-forming regions in Cygnus X, clarifying its structure and membership, and revealing that AFGL 2591 is much farther than previously thought.

Contribution

First precise parallax and proper motion measurements of multiple star-forming regions in Cygnus X, clarifying its three-dimensional structure and membership.

Findings

Most regions are at ~1.4 kpc, confirming they are part of Cygnus X.

AFGL 2591 is at a much greater distance (~3.33 kpc) than other regions.

The regions do not show signs of expansion, suggesting a different dynamic scenario.

Abstract

Whether the Cygnus X complex consists of one physically connected region of star formation or of multiple independent regions projected close together on the sky has been debated for decades. The main reason for this puzzling scenario is the lack of trustworthy distance measurements. We aim to understand the structure and dynamics of the star-forming regions toward Cygnus X by accurate distance and proper motion measurements. To measure trigonometric parallaxes, we observed 6.7 GHz methanol and 22 GHz water masers with the European VLBI Network and the Very Long Baseline Array. We measured the trigonometric parallaxes and proper motions of five massive star-forming regions toward the Cygnus X complex and report the following distances within a 10% accuracy: 1.30+-0.07 kpc for W 75N, 1.46^{+0.09}_{-0.08} kpc for DR 20, 1.50^{+0.08}_{-0.07} kpc for DR 21, 1.36^{+0.12}_{-0.11} kpc for IRAS20290+4052, and 3.33+-0.11kpc for AFGL 2591. While the distances of W 75N, DR 20, DR 21, and IRAS 20290+4052 are consistent with a single distance of 1.40+-0.08 kpc for the Cygnus X complex, AFGL 2591 is located at a much greater distance than previously assumed. The space velocities of the four star-forming regions in the Cygnus X complex do not suggest an expanding Stroemgren sphere.