ASTROMETRY OF IRAS 22555+6213 WITH VERA: A 3-DIMENSIONAL VIEW OF SOURCES ALONG THE SAME LINE OF SIGHT

Abstract

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 0.278±0.019 mas, corresponding to a distance of 3.66 −0.26 kpc. Our results confirm 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, 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 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 (−32 km s−1 lag) to be consistent with the parallax distance.