Annual parallax measurements of a Mira variable star, U Lyncis

Abstract

Abstract We have measured the annual parallax of the water maser around a Mira star, U Lyncis (U Lyn) with VLBI Exploration of Radio Astrometry (VERA). The value of the parallax is 1.27 ± 0.06 mas, corresponding to a distance of $786^{+40}_{-36}\:$pc. This is the first VLBI measurement of the parallax of U Lyn. We obtained the period and the apparent magnitude of U Lyn based on near-infrared observations with the Kagoshima University 1 m telescope. The period and the mean magnitude of the K′ band are 437.9 day and +1.15 ± 0.09 mag, respectively. Using our measured parallax and period, we find that the location of U Lyn on the period–luminosity plane is consistent with its nature as a Mira variable fundamental mode pulsator. Also, we estimated the distance using the period–luminosity relationship, our period and apparent magnitude and this gave a difference of about 100 pc between our parallactic distance and the distance estimated by using the period–luminosity relationship. We estimated the luminosity, radius, and mass of U Lyn to be 10100 ± 420 L⊙, 391 ± 34 R⊙, and 1.9 ± 0.7 M⊙, respectively. We found 50 water maser spots with a distribution ∼ 13 au around the star and the motion implies the existence of an outflow.