Parallax of a Mira variable R Ursae Majoris studied with astrometric VLBI

Akiharu Nakagawa; Tomoharu Kurayama; Makoto Matsui; Toshihiro Omodaka; Mareki Honma; Katsunori M Shibata; Katsuhisa Sato; Takaaki Jike

doi:10.1093/pasj/psw069

paper

Parallax of a Mira variable R Ursae Majoris studied with astrometric VLBI

arXiv:1607.01090 · doi:10.1093/pasj/psw069

Abstract

We have measured an annual parallax of the Mira variable R~Ursae~Majoris (R~UMa) with the VLBI exploration for Radio Astronomy (VERA). From the monitoring VLBI observations spanning about two years, we detected H $_{2}$ O maser spots in the LSR velocities ranges from 37 to 42 km\,s $^{- 1}$ . We derived an annual parallax of 1.97 $\pm$ 0.05\,mas, and it gives a corresponding distance of 508 $\pm$ 13\,pc. The VLBI maps revealed 72 maser spots distributed in $\sim$ 110 au area around an expected stellar position. Circumstellar kinematics of the maser spots were also revealed by subtracting a systemic motion in the Hipparcos catalog from proper motions of each maser spots derived from our VLBI observations. Infrared photometry is also conducted to measure a $K$ band apparent magnitude, and we obtained a mean magnitude of $m_{K}$ = 1.19 $\pm$ 0.02\,mag. Using the trigonometric distance, the $m_{K}$ is converted to a $K$ band absolute magnitude of $M_{K} = -$ 7.34 $\pm$ 0.06\,mag. This result gives a much more accurate absolute magnitude of R~UMa than previously provided. We solved a zero-point of $M_{K} - lo g P$ relation for the Galactic Mira variables and obtained a relation of $M_{K} = -$ 3.52 $lo g P$ + (1.09 $\pm$ 0.14). Other long period variables including red supergiants, whose distances were determined from astrometric VLBI, were also compiled to explore the different sequences of $M_{K} - lo g P$ relation.

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Parallax of a Mira variable R Ursae Majoris studied with astrometric VLBI

Abstract

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