Today's Colloquium: Tracing the Structure and Kinematics of the Milky Way through Astrometric VLBI Measurements

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Clik here to view.© Alberto Sanna

I will review the current state of the Bar and Spiral Structure Legacy Survey (BeSSeL). The BeSSeL Survey is a Very Long Baseline Array (VLBA) key science project to measure trigonometric parallaxes and proper motions of massive star-forming regions throughout the 1st, 2nd, and in the 3rd Galactic quadrant of the Milky Way. Sites of star formation which give birth to massive O-B stars trace rich gas condensations along spiral arm segments, and are therefore the most suitable targets to pinpoint the spiral structure of our Galaxy.

Very Long Baseline Interferometry (VLBI) observations of strong maser emission, associated with young massive stars, currently yield parallax accuracy as good as 10 micro-arcsecond. That allows us to explore our Galaxy reaching objects with distances more than 10 kpc away from the Sun, and still locating them with an accuracy better than 10%. Currently, over 100 trigonometric parallaxes and proper motions have been measured with the VLBA, the European VLBI Network, and the Japanese VLBI Exploration of Radio Astrometry facility. I will summarize the major achievements obtained so far and put them in the context of a global view of our own Galaxy.