Implication of the period-magnitude relation for massive AGB stars and its astronomical applications

We present astrometric very long baseline interferometry (VLBI) studies of AGB stars. To understand the properties and evolution of AGB stars, distances are an important parameter. The distribution and kinematics of their circumstellar matter are also revealed with the VLBI method. We used the VERA array to observe 22\,GHz H$_2$O masers in various subclasses of AGB stars. Parallaxes of the three OH/IR stars NSV17351, OH39.7$+$1.5, IRC$-$30363, and the Mira-type variable star AW~Tau were newly obtained. We present the circumstellar distribution and kinematics of H$_2$O masers around NSV17351. The absolute magnitudes in mid-infrared bands of OH/IR stars with very long pulsation periods were investigated and a period-magnitude relation in the WISE W3 band, $M_{\mathrm{W3}} = (-7.21\pm1.18)\log P + (9.25\pm3.09)$, was found for the Galactic AGB stars. The VLBI is still a powerful tool for parallax measurements of the Galactic AGB stars surrounded by thick dust shells.Comment: 24 pages, 8 figures, Proceedings of the IAU symposium 376, At the cross-roads of astrophysics and cosmology Period luminosity relations in the 2020

VLBI Observations of Water Masers in Onsala 1: Massive Binary Star Forming Site?

We present proper motions of water masers toward the Onsala 1 star forming region, observed with the Japanese VLBI network at three epochs spanning 290 days. We found that there are two water maser clusters (WMC1 and WMC2) separated from each other by 1".6 (2900 AU at a distance of 1.8 kpc). The proper motion measurement reveals that WMC1 is associated with a bipolar outflow elongated in the east-west direction with an expansion velocity of 69+-11 km/s. WMC1 and WMC2 are associated with two 345 GHz continuum dust emission sources, and located 2" (3600 AU) east from the core of an ultracompact HII region traced by 8.4 GHz radio continuum emission. This indicates that star formation activity of Onsala 1 could move from the west side of ultracompact HII region to the east side of two young stellar objects associated with the water masers. We also find that WMC1 and UC HII region could be gravitationally bound. Their relative velocity along the line of sight is 3 km/s, and total mass is 37 Mo. Onsala 1 seems to harbor a binary star at different evolutionary stage.Comment: 9 pages, 4 figures, accepted for PAS