Proper motion and parallaxes of radio stars will enable us to align the latest International Celestial Reference Frame (ICRF3) based on VLBI observations with the optical astrometric catalogue obtained by the Gaia mission. The Gaia mission has observed approximately 500,000 extragalactic objects in optical with a competitive precision, and produced an independent astrometric catalogue of 2820 objects common to the ICRF2 (Gaia Collaboration et al. 2018) and contains astrometric solutions of parallaxes and proper motions for significant amount of stars. This provides a rare opportunity for independent verification of the VLBI astrometric catalogues. However, due to an average parallax zero-point of -29 µas of the Gaia catalogue (Lindegren et al. 2018), independent assessment of the Gaia parallaxes is required. Unfortunately, very few optically bright radio stars were observed with VLBI, therefore it is important to identify more Galactic stars that could be observed by both VLBI and optical mission for the parallax verification.
Here we show the astrometric results for five radio stars (HR1099, UX Ari, HR132742, HR5907 and LSI+61 303) in several VLBI experiments between 2015 and 2019.
Presented at the Journees 2019 7-9 October, Paris Observatory.