We report on a measurement of the trigonometric parallax of IRAS 05168$ +$ 3634 with VERA. The parallax is 0.532 $ \pm$ 0.053 mas, corresponding to a distance of 1.88$ ^{+0.21}_{-0.17}$ kpc. This result is significantly smaller than the previous distance estimate of 6 kpc, based on the kinematic distance. This drastic change in the source distance revises not only the physical parameters of IRAS 05168$ +$ 3634, but also its location of the source, placing it in the Perseus arm, rather than the Outer arm. We also measured the proper motions of the source. A combination of the distance and the proper motions with the systemic velocity yields a rotation velocity ($ \Theta$ ) of 227$ ^{+\ 9}_{-11}$ km s$ ^{-1}$ at the source, assuming $ \Theta_{\rm {0}}$$ =$ 240 km s$ ^{-1}$ . Our result combined with previous VLBI results for six sources in the Perseus arm indicates that the sources rotate systematically slower than the Galactic rotation velocity at the LSR. In fact, we show observed disk peculiar motions averaged over the seven sources in the Perseus arm as ($ U_{\rm {mean}}$ , $ V_{\rm {mean}}$ ) $ =$ (11 $ \pm$ 3, $-$ 17 $ \pm$ 3) km s$ ^{-1}$ , indicating that these seven sources are systematically moving toward the Galactic center, and lag behind the Galactic rotation.

We present the astrometric VLBI observations of H 2 O masers associated with IRAS 22480+6002 (= IRC+60370, hereafter I22480) with the VLBI Exploration of Radio Astrometry (VERA). The stellar type of I22480 looks unusual as a stellar maser source and has been debated since the 1970s. We successfully determined the annual parallax of a group of the H 2 O maser spots, π = 0.400 ± 0.025 mas, corresponding to a distance to I22480 of D = 2.50 +0.17 −0.15 kpc. This suggests that the estimated bolometric luminosity of I22480 should be revised to 35 000 L ⊙ , favoring a K-type supergiant rather than an RV Tau-type variable star previously suggested. Although the spectral type is unusual as a stellar maser source, the internal motions of the H 2 O maser features suggest that the H 2 O masers are associated with the circumstellar envelope of this star. Taking into account a possible stellar motion with respect to the maser feature motions, we derived a secular proper motion of I22480, (µ α , µ δ ) = (−2.58 ± 0.33, −1.91 ± 0.17) [mas yr −1 ]. The derived motion of I22480 in the Milky Way has a deviation by ∼ −30 km s −1 in the galactic azimuthal direction from a circular motion estimated from the galactocentric distance to I22480 and assumption of a flat Galactic rotation curve. This peculiar motion is still comparable to those typically seen in the H 2 O maser sources located in the Perseus spiral arm. Taking into account the peculiar motion and the proximity to the Galactic midplane (z ≃60 pc), I22480 may be a member of the Galactic thin disk.

1We report the results of the measurement of the trigonometric parallax of an H 2 O maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be 0.314±0.070 mas, corresponding to a distance of 3.18 +0.90 −0.66 kpc. Our results confirm IRAS 22555+6213 to be located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to beand W src are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC 7538 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 NGC 7538 are associated with the Perseus Arm, while Cepheus A is located in the Local Arm. We compared the kinematic distances of IRAS 22198+6336, G108.18+05.51, G108.20−00.58, G108.47+02.81, G108.59+00.49, Cepheus A, NGC 7538, G111.23−01.23, G111.25−00.76 and IRAS 22555+6213 derived with flat and non-flat rotation curve with its parallax distance and found the kinematic distance derived from the non-flat rotation assumption (−5 to −39 km s −1 lag) to be consistent with the parallax distance.

We aim to reveal the mass distribution of the Galaxy based on a precise rotation curve constructed using VERA observations. We have been observing Galactic H2O masers with VERA. We here report one of the results of VERA for IRAS 05168+3634. The parallax is 0.532 ± 0.053 mas which corresponds to a distance of 1.88+0.21−0.17 kpc, and the proper motions are (μαcosδ, μδ) = (0.23 ± 1.07, −3.14 ± 0.28) mas yr−1. The distance is significantly smaller than the previous distance estimate of 6 kpc based on a kinematic distance. This drastic change places the source in the Perseus arm rather than in the Outer arm. Combination of the distance and the proper motions with the systemic velocity provides a rotation velocity of 227+9−11 km s−1 at the source assuming Θ0 = 240 km s−1. The result is marginally slower than the rotation velocity at LSR with ~ 1−σ significance, but consistent with previous VLBI results for six sources in the Perseus arm. We also show the averaged disk peculiar motion over the seven sources in the Perseus arm as (Umean, Vmean) = (11 ± 3, −17 ± 3) km s−1. It suggests that the seven sources in the Perseus arm are systematically moving toward the Galactic center, and lag behind the Galactic rotation with more than 3-σ significance.

Abstract. We present a measurement of the trigonometric parallax of IRAS 05168+3634 with VERA. The parallax is 0.532 ± 0.053 mas, corresponding to a distance of 1.88 +0.21 −0.17 kpc. This is significantly closer than the previous distance estimate of 6 kpc based on a kinematic distance measurement. This drastic change in the source distance implies the need for revised values of not only the physical parameters of IRAS 05168+3634, but it also implies a different location in the Galaxy, placing it in the Perseus arm rather than the Outer arm. We also measured the proper motion of the source. A combination of the distance and proper motion with the systemic velocity yields a rotation velocity Θ = 227 +9 −11 km s −1 at the source position, assuming Θ0 = 240 km s −1 . Our result, combined with previous VLBI results for six sources in the Perseus arm, indicates that the sources rotate systematically more slowly than the Galactic rotation velocity at the local standard of rest. In fact, we derive peculiar motions in the disk averaged over the seven sources in the Perseus arm of (Umean, Vmean) = (11 ± 3, −17 ± 3) km s −1 , which indicates that these seven sources are moving systematically toward the Galactic Center and lag behind the overall Galactic rotation.