Trigonometric Parallax of IRAS 22555+6213 with VERA: 3-Dimensional View of Sources Along the Same Line of Sight

TL;DR

This study measures the parallax of an H2O maser source using VERA, confirming its location in the Perseus arm and providing insights into its 3D position and motion within the Milky Way.

Contribution

First precise parallax measurement of 22 with VERA, establishing its distance and Galactic arm placement, and comparing kinematic and parallax distances for multiple sources.

Findings

22 is located in the Perseus arm at 3.18 kpc.

The peculiar motion of 22 is (4, -32, 8) km/s.

Kinematic distances from non-flat rotation models agree with parallax distances.

Abstract

We report the results of the measurement of the trigonometric parallax of an H$_2$O maser source in \r22 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be 0.314$\pm$0.070~mas, corresponding to a distance of 3.18$^{+0.90}_{-0.66}$~kpc. Our results confirm \r22 to be located in the Perseus arm. We computed the peculiar motion of \r22 to be $(U_{src}, V_{src}, W_{src}) = (4\pm4, -32\pm6, 8\pm6)$~\kms, where $U_{src}$, $V_{src}$, and $W_{src}$ are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. \r22, NGC\,7538 and Cepheus A lie along the same line of sight, and are within 2$^{\circ}$ on the sky. Their parallax distances with which we derived their absolute position in the Milky Way show that \r22 and \ngc~are associated with the Perseus Arm, while \cepa~is located in the Local Arm. We compared the kinematic distances of \iras, \ga, \gb, \gc, \gd, \cepa, \ngc, \ge, \gf~and \r22~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 \kms~lag) to be consistent with the parallax distance.