VLBI astrometry of long period variables using VERA

Title: VLBI astrometry of long period variables using VERA
Speaker:  Assistant Prof.  Akiharu Nakagawa  (Kagoshima University, Japan)
Location: Small Conference Room, 3rd Floor
Time: 10:00 AM – 11:30 AM, November  29 (Friday), 2019
Long period variables (LPVs) have initial mass of 0.8 to 8 solar mass and show stellar pulsation with typical periods of 100 to 1000 days. They represent large mass loss ratio of 10^7 solar mass/yr, and sometimes it reaches 10^4 solar mass/yr. For this reason, LPVs are important objects to understand chemical property and chemical evolution of our Galaxy and universe. In Kagoshima University, we have been conducting 22GHz astrometric VLBI observations of LPVs using a Japanese VLBI array VERA. Initial interest of our study was a confirmation of Period-luminosity relation (PLR) of the Galactic Mira variable stars. We have observed dozens of Mira variables showing typical pulsation periods of ~1 yr. By observing the Galactic Mira variables, we confirmed a PLR and reported it in Nakagawa et al. (2016). Recently, we started VLBI observations towards OH/IR stars at 22GHz and also at 43GHz. Miras are thought to be progenitors of OH/IR stars. From the new observations, we aim to reveal evolution of LPVs from Miras to OH/IR stars. In my talk, I will mainly present our observational studies about LPVs, and finally, I will quickly show comparison of astrometric results between VLBI and Gaia.