2014/04/28 by Yoshiharu Asaki, Y. Asaki, Hiroshi Imai +5
Physics and Astronomy · #Astrometry #Astrophysics and Cosmic Phenomena #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Kinematics #Maser #Parallax #Proper motion #Very-long-baseline interferometry #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/787/1/54
Astrophysical Journal, in press
arxiv created 2014/04/28 · openalex publication_date 2014/05/02 · arxiv updated 2015/06/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present astrometric analysis of archival data of water masers in the star-forming region Sharpless 269 (S269) IRS 2w, observed with the VLBI Exploration of Radio Astrometry. An annual parallax of one of the bright maser features in this region was previously reported to be 0.189 ± 0.008 milliarcsecond (mas) using part of the same archival data as we used. However, we found that this maser feature is not the best to represent the annual parallax to S269 IRS 2w because the morphology is remarkably elongated in the east–west direction. For this study we have selected another maser feature showing simpler morphology. This makes the new annual parallax estimate more credible. Our newly obtained annual parallax is 0.247 ± 0.034 mas, corresponding to kpc. This value is well consistent with the 3.7–3.8 kpc obtained using the kinematic distance estimates and photometric distance modulus. We considered two hypotheses for the water-maser spatial distribution, a bipolar outflow and an expanding ring, in a kinematic model fitting analysis with a radially expanding flow. At this stage, any conclusions about the systemic proper motion could not be drawn from the kinematic analysis. Alternatively, we evaluated the mean proper motion to be (0.39 ± 0.92, −1.27 ± 0.90) mas yr −1 eastward and northward, respectively, from the obtained proper motions of the detected water-maser features. The newly obtained annual parallax and mean proper motion give the peculiar motion of S269 IRS 2w to be ( U s , V s , W s ) of (8 ± 6, −21 ± 17, 1 ± 18) km s −1 .