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

Understand

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.