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Register a new userH2O maser motions and the distance of the star forming region G192.16-3.84
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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.
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Previous observations have revealed an accretion disk and outflow motion in high-mass star-forming region G192.16-3.84. While collapse have not been reported before. We present here molecular line and continuum observations toward massive core G192.16-3.84 with the Submillimeter Array. C$^{18}$O(2-1) and HCO$^{+}$(3-2) lines show pronounced blue profiles, indicating gas infalling in this region. This is the first time that the infall motion has been reported in G192.16-3.84 core. Two-layer model fitting gave infall velocities of 2.0$pm$0.2 and 2.8$pm$0.1 km s$^{-1}$. Assuming that the cloud core follows a power-law density profile ($rho$$propto$$r^{1.5}$), the corresponding mass infall rates are (4.7$pm$1.7)$times10^{-3}$ and (6.6$pm$2.1)$times10^{-3}$ M$_{sun}$ yr$^{-1}$ for C$^{18}$O(2-1) and HCO$^{+}$(3-2), respectively. The derived infall rates are in agreement with the turbulent core model and those in other high-mass star-forming regions, suggesting that high accretion rate is a general requirement to form a massive star.
We report H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japan VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole h2o maser region in G192.16-3.84, containing two young stellar objects separated by ~1200 AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly-collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of ~100 km/s and re-estimated a dynamical age of the whole jet to be 5.6x10^4 yrs. We have investigated the spatial distribution of Doppler velocities during the previous and present observations and relative proper motions of H2O maser features in the southern cluster, and a relative bulk motion between the two maser clusters. They are well explained by a model of an infalling-rotating disk with a radius of ~1000 AU and a central stellar mass of 5-10 M_sun, rather than by a model of a bipolar jet perpendicular to the observed CO outflow. Based on the derived H2O maser spatio-kinematical parameters, we discuss the formation mechanism of the massive young stellar objects and the outflow development in G192.16-3.84.
We performed astrometric observations with the VLBA of WB89-437, an H2O maser source in the Outer spiral arm of the Galaxy. We measure an annual parallax of 0.167 +/- 0.006 mas, corresponding to a heliocentric distance of 6.0 +/- 0.2 kpc or a Galactocentric distance of 13.4 +/- 0.2 kpc. This value for the heliocentric distance is considerably smaller than the kinematic distance of 8.6 kpc. This confirms the presence of a faint Outer arm toward l = 135 degrees. We also measured the full space motion of the object and find a large peculiar motion of ~20 km/s toward the Galactic center. This peculiar motion explains the large error in the kinematic distance estimate. We also find that WB89-437 has the same rotation speed as the LSR, providing more evidence for a flat rotation curve and thus the presence of dark matter in the outer Galaxy.
We have used the VLBA to measure the annual parallax of the H2O masers in the star-forming region IRAS 00420+5530. This measurement yields a direct distance estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the standard kinematic distance estimate of ~4.6 kpc (according to the rotation curve of Brand and Blitz 1993), as well as most of the broad range of distances (1.7-7.7 kpc) used in various astrophysical analyses in the literature. The 3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate distance implies a substantial non-circular and anomalously slow Galactic orbit, consistent with similar observations of W3(OH) (Xu et al., 2006; Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of the Galaxy is thus more than a factor of two closer than previously presumed, and exhibits motions substantially at odds with axisymmetric models of the rotating Galaxy.
Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.
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