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Register a new userWater maser motions in W3(OH) and a determination of its distance
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We report phase-referencing VLBA observations of H2O masers near the star-forming region W3(OH) to measure their parallax and absolute proper motions. The measured annual parallax is 0.489 +/- 0.017 milli-arcseconds (2.04 +/- 0.07 kpc), where the error is dominated by a systematic atmospheric contribution. This distance is consistent with photometric distances from previous observations and with the distance determined from CH3OH maser astrometry presented in a related paper. We also find that the source driving the H2O outflow, the ``TW-object, moves with a 3-dimensional velocity of > 7 km/s relative to the ultracompact HII region W3(OH).
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We present the first 6.7 GHz methanol maser linear polarization map of the extended filamentary maser structure around the compact HII region W3(OH). The methanol masers show linear polarization up to 8 per cent and the polarization angles indicate a magnetic field direction along the North-South maser structure. The polarization angles are consistent with those measured for the OH masers, taking into account external Faraday rotation toward W3(OH), and confirm that the OH and methanol masers are found in similar physical conditions. Additionally we discuss the Zeeman splitting of the 6.7 GHz methanol transition and present an upper limit of ~22 mG for the magnetic field strength in the maser region. The upper limit is fully consistent with the field strengths derived from OH maser Zeeman splitting.
We present Very Long Baseline Array observations of the kinematics of the water masers associated with OH 12.8-0.9, the fourth member of the so-called water fountain class of sources. We find that the masers occupy two distinct regions at the ends of a bipolar jet-like structure oriented north-south, with the blue-shifted masers located to the north and the red-shifted masers to the south. The masers are distributed along arc-like structures 12-20 mas across oriented perpendicular to the separation axis with an angular separation of ~110 mas on the sky. Our multi-epoch observations, show the two maser arcs to be expanding away from each other along the axis of separation. The relative proper motions of the two maser regions is 2.7 mas/yr (~105 km/s at the assumed distance of 8 kpc). The measured radial velocity difference between the northern, blue-shifted masers and the southern, red-shifted masers is 48.4 km/s. The radial velocity, when combined with the proper motion, yields a three-dimensional expansion velocity of 58 km/s and an inclination angle of 24 deg. for the jet. By combining our radial velocities with historical values, we estimate the three dimensional acceleration of the masers to be ~0.63 km/s/yr and a dynamical age for the collimated outflow of ~90 yr.
We report on the results of a 14 year long VLBI study of proper motions in the IC133 H2O maser source in the galaxy M33. The method of Ordered Motion Parallax was used to model the 3-dimensional structure and dynamics of IC133 and obtain a distance estimate, 800 +/- 180 kpc. Our technique for determining the distance to M33 is independent of calibrations common to other distance indicators, such as Cepheid Period-Luminosity relations, and therefore provides an important check for previous distance determinations.
We present the results of astrometic observations of H2O masers associated with the star forming region G192.16-3.84 with the VLBI Exploration of Radio Astrometry (VERA). The H2O masers seem to be associated with two young stellar objects (YSOs) separated by sim1200 AU as reported in previous observations. In the present observations, we successfully detected an annual parallax of 0.66 pm 0.04 mas for the H2 O masers, which corresponds to a distance to G192.16-3.84 of D = 1.52 pm 0.08 kpc from the Sun. The determined distance is shorter than the estimated kinematic distance. Using the annual parallax distance and the estimated parameters of the millimeter continuum emission, we estimate the mass of the disk plus circumstellar cloud in the southern young stellar object to be 10.0+4.3Mcdot. We also estimate the galactocentric distance and the peculiar motion -3.6 of G192.16-3.84, relative to a circular Galactic rotation: Rstar = 9.99 pm 0.08 kpc, Zstar = -0.10 pm 0.01 kpc, and (Ustar,Vstar,Wstar)=(-2.8pm1.0,-10.5pm0.3,4.9pm2.7)[kms-1]respectively. The peculiar motion of G192.16-3.84 is within that typically found in recent VLBI astrometric results. The angular distribution and three-dimensional velocity field of H2O maser features associated with the northern YSO indicate the existence of a bipolar outflow with a major axis along the northeast-southwest direction.
We present results of our diffraction-limited mid-infrared imaging of the massive star-forming region W3(OH) with SpectroCam-10 on the 5-m Hale telescope at wavelengths of 8.8, 11.7, and 17.9 micron. The thermal emission from heated dust grains associated with the ultracompact HII region W3(OH) is resolved and has a spatial extent of ~2 arcsec in the N band. We did not detect the hot core source W3(H_2O) which implies the presence of at least 12 mag of extinction at 11.7 micron towards this source. These results together with other data were used to constrain the properties of W3(OH) and W3(H_2O) and their envelopes by modelling the thermal dust emission.
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