Abstract
As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151 ± 0.042 mas, which corresponds to a distance of $D = 6.61^{+2.55}_{-1.44}\:{\rm kpc}$, and the obtained proper motion components were $(\mu _\alpha {\rm cos}\delta ,\, \mu _\delta ) = (-1.44 \pm 0.15,\, -0.27 \pm 0.16)\:{\rm mas\:yr^{-1}}$ in equatorial coordinates. Assuming Galactic constants of $(R_0,\, \Theta _0) = (8.05 \pm 0.45\:{\rm kpc},\, 238 \pm 14\:{\rm km\:s^{-1}})$, the Galactocentric distance and rotation velocity were measured to be $(R,\, \Theta ) = (13.04 \pm 2.24\:{\rm kpc},\, 239 \pm 22\:{\rm km\:s^{-1}})$, which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, $L_{\rm Bol} = (3.11 \pm 2.86) \times 10^{3}\, L_{\odot }$, which corresponds to a spectral type of B1–B2. Analysis of ${}^{12}{\rm{CO}}$ (J = 1–0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which matches well a structure predicted by numerical simulation of the cloud–cloud collision phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of the two initial clouds was as slow as 3–$5\:{\rm km\, s^{-1}}$, which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (∼3–5 km s−1), as suggested by Takahira, Tasker, and Habe (2014, ApJ, 792, 63).
Estimation of the solar galactocentric distance and galactic rotation velocity from near-solar-circle objects
