- evn2024@mpifr.de
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Contribution
VLBI astrometry for OH/IR stars and Period-Luminosity relation in very long period range
Speakers
- Dr. Akiharu NAKAGAWA
Primary authors
- Dr. Akiharu NAKAGAWA (Kagoshima Univ.)
Co-authors
- Dr. Ryosuke WATANABE (Kagoshima Univ.)
- Dr. Tomoharu KURAYAMA (Teikyo University of Science)
- Dr. Hiroshi SUDOU (National Institute of Technology, Sendai College)
- Dr. Gabor OROSZ (JIVE)
- Dr. Takafumi KAMIZUKA (The University of Tokyo)
- Dr. Kengo TACHIBANA (The University of Tokyo)
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Content
We will present astrometric VLBI studies for OH/IR stars conducted with the Japanese VLBI array VERA (VLBI Exploration of Radio Astrometry). Using several OH/IR stars, we have been explored period-luminosity relation (PLR) in the quite long pulsation period range ($\geq$1000 d). A preliminary result of the new PLR will be presented. We will emphasize advantages of VLBI in parallax measurements of dust-obscured stars, and complementarity between VLBI and Gaia will also be mentioned.
In a late stage of stellar evolution with initial masses of $0.8-10M_{\odot}$, they spend time as Asymptotic Giant Branch (AGB) stars. Mira variables are thought to be in early phase of the AGB exhibiting a PLR, which is a well known tool for distance estimation. As they evolve, they will be surrounded by dust shells. Then, due to detection of OH masers and IR excess, they will be recognized as OH/IR stars. Due to extinction by circumstellar dust, parallax measurements of the OH/IR stars in optical bands are difficult. However, VLBI astrometry for H$_2$O masers associated with the OH/IR stars are effective to measure their parallaxes. Since OH/IR stars with thick dust shells tend to show quite long pulsation periods ($P \geq$1000 days), extensions of the PLR to longer period range may provide new distance estimator for the OH/IR stars. Since they are more massive than typical Mira variables, they can also be used in the study of Galactic dynamics.
At the EVN symposium 2016, we reported the start of new research targeting the OH/IR stars with very long periods. Now, eight years later, we have been observed OH/IR stars with periods of 500-1500 days. We present current status of our studies using an OH/IR star NSV17351 together with parallaxes of other sources. A prelimialy result of the PLR of $ M_{\mathrm{bol}} = (-3.31 \pm 0. 08) \log P+(-3.94 \pm 0.20) $ was obtained considering spectral energy distributions (SEDs) of the sources.