JVN observations of H2O masers around the evolved star IRAS 22480+6002

We report on the H2O maser distributions around IRAS 22480+6002 (=IRC+60370) observed with the Japanese VLBI Network (JVN) at three epochs spanning 2 months. This object was identified as a K-type supergiant in 1970s, which was unusual as a stellar maser source. The spectrum of H2O masers consists of 5 peaks separated roughly equally by a few km/s each. The H2O masers were spatially resolved into more than 15 features, which spread about 50 mas along the east--west direction. However, no correlation was found between the proper motion vectors and their spatial distributions; the velocity field of the envelope seems random. A statistical parallax method applied to the observed proper-motion data set gives a distance of 1.0+-0.4 kpc for this object, that is considerably smaller than previously thought. The distance indicates that this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and optical characteristics quite similar to those of the population II post-AGB stars such as RV Tau variables.Comment: 7 pages, 5 figures, PASJ 60, No. 1 (2008 Feb. 25 issue) in press. High res. figures available at ftp://ftp.nro.nao.ac.jp/nroreport/no657.pdf.g

A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O maser emission

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.Comment: 30 pages, 3 figures, 3 tables, to be published in the Publication of the Astronomical Society of Japan issued on 2006 October 2

3-D Kinematics of Water Masers in the W51A Region

We report proper motion measurements of water masers in the massive-star forming region W51A and the analyses of the 3-D kinematics of the masers in three maser clusters of W51A (W51 North, Main, and South). In W~51 North, we found a clear expanding flow that has an expansion velocity of ~70 km/s and indicates deceleration. The originating point of the flow coincides within 0.1 as with a silicon-monoxide maser source near the HII region W~51d. In W51 Main, no systematic motion was found in the whole velocity range (158 km/s =< V(lsr) =< -58 km/s) although a stream motion was reported previously in a limited range of the Doppler velocity (54 km/s =< V(lsr) =< 68 kms). Multiple driving sources of outflows are thought to explain the kinematics of W51 Main. In W51 South, an expansion motion like a bipolar flow was marginally visible. Analyses based on diagonalization of the variance-covariance matrix of maser velocity vectors demonstrate that the maser kinematics in W51 North and Main are significantly tri-axially asymmetric. We estimated a distance to W51 North to be 6.1 +/- 1.3 kpc on the basis of the model fitting method adopting a radially expanding flow.Comment: 20 pages, 8 figures, 8 tables, appear in the NRO report No. 564 (ftp://ftp.nro.nao.ac.jp/nroreport/PASJ-W51.pdf) and will appear in Publ. Astron. Soc. Japan, Vol. 54, No. 5 (10/25 issue

A Complete Survey of the Central Molecular Zone in NH3

We present a map of the major part of the central molecular zone (CMZ) of simultaneous observations in the NH3 (J,K) = (1,1) and (2,2) lines using the Kagoshima 6-m telescope. The mapped area is -1.000 < l < 1.625 deg, -0.375 < b < +0.250 deg. The kinetic temperatures derived from the (2,2) to (1,1) intensity ratios are 20--80 K or exceed 80 K. The gases corresponding to temperature of 20--80 K and > 80 K contain 75% and 25% of the total NH3 flux, respectively. These temperatures indicate that the dense molecular gas in the CMZ is dominated by gas that is warmer than the majority of the dust present there. A comparison with the CO survey by Sawada et al. (2001) shows that the NH3 emitting region is surrounded by a high pressure region on the l-v plane. Although NH3 emission traces dense gas, it is not extended into a high pressure region. Therefore, the high pressure region is less dense and has to be hotter. This indicates that the molecular cloud complex in the Galactic center region has a ``core'' of dense and warm clouds which are traced by the NH3 emission, and an ``envelope'' of less dense and hotter gas clouds. Besides heating by ambipolar diffusion, the hot plasma gas emitting the X-ray emission may heat the hot ``envelope''.Comment: 21 pages, 14 figures, accepted for PAS