The Gould Belt, the de Vaucouleurs-Dolidze Belt, and the Orion Arm

TL;DR

This study refines the spatial orientation of the Local (Orion) arm and the de Vaucouleurs-Dolidze belt using maser data, revealing their alignment and structure, and providing new estimates of their parameters.

Contribution

It offers new measurements of the Local arm's orientation and pitch angle, and clarifies the relationship between the de Vaucouleurs-Dolidze belt and the Local arm.

Findings

The Local arm is elongated with a narrow ellipsoid, inclined at 5.6° to the Galactic plane.

The de Vaucouleurs-Dolidze belt aligns with the Local arm, forming a continuous band.

The third axis of maser position ellipsoid aligns with the Galactic pole.

Abstract

Based on masers with measured trigonometric parallaxes, we have redetermined the spatial orientation parameters of the Local (Orion) arm. Using 23 sources (the Gould Belt objects were excluded), we have found that their spatial distribution can be approximated by a very narrow ellipsoid elongated in the direction L_1=77.1+/-2.9^o whose symmetry plane is inclined to the Galactic plane at an angle of 5.6+/-0.2^o. The longitude of the ascending node of the symmetry plane is l_\Omega=70+/-3^o. A new estimate for the pitch angle of the Local spiral arm has been obtained by an independent method: i=12.9+/-2.9^o. Previously, a belt of young B stars, the de Vaucouleurs.Dolidze belt, was pointed out on the celestial sphere with parameters close to such an orientation. We have refined the spatial orientation parameters of this belt based on a homogeneous sample of protostars. The de Vaucouleurs.Dolidze belt can be identified with the Local arm, with the belt proper as a continuous band on the celestial sphere like the Gould Belt being absent due to the peculiarities of the spatial orientation of the Local arm. Using the entire sample of 119 Galactic masers, we have shown that the third axis of their position ellipsoid has no deviation from the direction to the Galactic pole: B_3=89.7+/-0.1^o.