The trigonometric parallax of IRAS 23385+6053 and physical properties of molecular clouds based on the VLBI astrometry

Abstract

We performed very long baseline interferometry (VLBI) observations to measure the trigonometric parallax of H${}_2$O maser sources in the outer massive star-forming region IRAS 23385+6053 using the VLBI Exploration of Radio Astrometry (VERA) in Japan. The annual parallax is $\pi =0.460\pm 0.086$~mas, which corresponds to a distance of $2.17_{-0.34}^{+0.50}$ kpc, roughly half the kinematic distance of 4.9 kpc reported in previous studies. The proper motion of IRAS 23385+6053 is obtained to be (${\mu }_{\alpha }\cos \delta$,${\mu }_{\delta }$)=($-3.73\pm 0.53$, $-2.07\pm 0.73$) mas yr${}^{-1}$. Based on VLBI astrometry result, we derived the physical properties of molecular clouds in which H${}_2$O masers have been detected, including IRAS 23385+6053 in the Cepheus and Cassiopeia region. We discuss the line-of-sight structures of the giant molecular clouds using the trigonometric distances obtained from the H${}_2$O maser sources. Our results suggest that molecular clouds in the Perseus arm extend over approximately $2$ kpc at the Cepheus and Cassiopeia region.

15 pages, 10 figures, 4 tables, accepted for Publications of the Astronomical Society of Japan (PASJ)