The calibration of the period luminosity relation (PLR) for Galactic Mira variables is one of the principle aims of the VERA project. We observe H2O maser emission at 22 GHz associated with Mira variables in order to determine their distances based on annual parallaxes. We conduct multi-epoch VLBI observations over 1{2 years with a typical interval of one month using VERA in order to obtain annual parallaxes with an accuracy of better than than 10%. Recently, the annnual parallax of T Lep was determined to be 3.060.04 mas corresponding to a distance of 3274 pc (Nakagawa et al., 2014). The circumstellar distribution and kinematics of H2O masers was also revealed. With accurate distances to the sources, calibrations of K-band absolute magnitudes (MK) can be improved compared to conventional studies. By compiling Mira variables whose distances were determined with astrometric VLBI, we obtained a PLR of MK = 3.51 logP + 1.37 ± 0.07.

We report our measurements of the trigonometric distance and proper motion of IRAS 20056+3350, obtained from the annual parallax of H2O masers. Our distance of D = 4:69+0:65 -0:51 kpc, which is 2.8 times larger than the near kinematic distance adopted in the literature, places IRAS 20056+3350 at the leading tip of the Local arm and proximal to the Solar circle. We estimated the proper motion of IRAS 20056+3350 to be (μα cos δ, μδ) = (—2:62 ± 0:33, —5:65 ± 0:52) mas yr-1 from the group motion of H2O masers, and use our results to estimate the angular velocity of Galactic rotation at the Galactocentric distance of the Sun, Ω0 = 29:75 ± 2:29 km s-1 kpc-1, which is consistent with the values obtained for other tangent points and Solar circle objects.

We report results of the measurement of the trigonometric parallax of an H2O maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be 0.2780.019 mas, corresponding to a distance of 3.66+0:30 -0:26 kpc. Our results conrm that IRAS 22555+6213 is located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to be (Usrc; Vsrc;Wsrc) = (0 ± 1,-32 ± 1, 9 ± 1) km s􀀀1, where Usrc, Vsrc, and Wsrc are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC7538 and Cepheus A lie along the same line of sight, and are within 2 on the sky. Their parallax distances, with which we derived their absolute position in the Milky Way, show that IRAS 22555+6213 and NGC7538 are associated with the Perseus arm, while Cepheus A is located in the Local arm. We compared the kinematic distances of IRAS 22555+6213 derived with at and non- at rota- tion curve with its parallax distance and found the kinematic distance derived from the non- at rotation assumption (—32 km s-1 lag) to be consistent with the parallax distance.

We made phase-referencing Very Long Baseline Interferometry (VLBI) observations of Galactic 22 GHz H2O maser sources with VLBI Exploration of Radio Astrometry (VERA). We measured the parallax dis- tances of G48.61+0.02, G48.99-0.30, G49.19-0.34, ON1, IRAS 20056+3350, IRAS 20143+3634, ON2N, and IRAS 20126+4104, which are located near the tangent point and the Solar circle. The angular ve- locity of the Galactic rotation at the LSR (i.e. the ratio of the Galactic constants) is derived using the measured parallax distances and proper motions of these sources. The derived value of Ω0 = 28:8  1:7 km s-1 kpc-1 is consistent with recent values obtained using VLBI astrometry but 10% larger than the International Astronomical Union (IAU) recommended value of 25.9 km s-1 kpc-1 = (220 km s-1) / (8.5 kpc).