The Bar and Spiral Structure Legacy (BeSSeL) Survey: Mapping the Milky Way with VLBI Astrometry

TL;DR

The BeSSeL Survey uses VLBI astrometry of masers to refine the Milky Way's spiral structure and fundamental parameters, challenging previous standard values and providing updated measurements of the Galaxy's center distance and rotation speed.

Contribution

This paper updates Milky Way parameters using VLBI maser data, incorporating recent Solar motion knowledge, and suggests revisions to standard Galactic constants.

Findings

R0 = 8.3 ± 0.23 kpc, Theta0 = 239 or 246 ± 7 km/s

Rules out the 8.5 kpc and 220 km/s standard model

Provides outlook for future BeSSeL observations

Abstract

Astrometric Very Long Baseline Interferometry (VLBI) observations of maser sources in the Milky Way are used to map the spiral structure of our Galaxy and to determine fundamental parameters such as the rotation velocity ($\Theta_0$) and curve and the distance to the Galactic center (R$_0$). Here, we present an update on our first results, implementing a recent change in the knowledge about the Solar motion. It seems unavoidable that the IAU recommended values for R$_0$ and $\Theta_0$ need a substantial revision. In particular the combination of 8.5 kpc and 220 \kms\, can be ruled out with high confidence. Combining the maser data with the distance to the Galactic center from stellar orbits and the proper motion of Sgr\,A* gives best values of R$_0$ = 8.3 $\pm$ 0.23 kpc and $\Theta_0$ = 239 or 246 $\pm$ 7 \kms, for Solar motions of V$_ \odot$ = 12.23 and 5.25 \kms, respectively. Finally, we give an outlook to future observations in the Bar and Spiral Structure Legacy (BeSSeL) Survey.