Shuji Deguchi

Kinematics and Distance of Water Masers in W3 IRS 5

We have made multiepoch VLBA observations of water masers in the massive-star forming region W3 IRS 5. We measured radial velocities and proper motions of 108 water maser features during three observing sessions. The masers are clustered in two groups, which are associated with at least two different outflows. Positions of the outflow origins are close to the hypercompact radio continuum sources, which are clustered within a scale of 6000 AU. The continuum sources are probably driving sources of the outflows. We performed a three-dimensional kinematic model analysis of the maser motions in one of the two outflows, assuming a spherically symmetric expanding flow. We obtained a distance to the W3 IRS 5 region as 1.83 ? 0.14 kpc. The directions of the two outflows are roughly in the north-south direction, which is not significantly different from the direction of the global outflow seen in CO (J = 2-1) emission. This suggests that the massive-star cluster in the W3 IRS 5 region was created during formation of hierarchical structure in a parent molecular-cloud core. Such a structure is expected to preserve the angular momentum vector during star formation process, which may be along the directions of the present outflows.

Laboratory microwave spectroscopy of the linear C3H and C3D radicals and related astronomical observation

Laboratory observations of rotational spectral lines of the C{sub 3}H and C3D radicals in their ground and vibrationally excited states are compared with astronomical observations with the Nobeyama Radio Observatorys 45-m radio telescope carried out toward IRC + 10216 in May 1988. The C{sub 3}H radical is found to have an extremely low vibrationally excited state, nu4(2Sigma mu), caused by the Renner-Teller effect in the nu4 (CCH bending) state. The radio telescope observations failed to detect the lines of the vibrationally excited C3H at the rms noise level of 24 mK. The upper limit to the column density of the nu4(2Sigma mu) is estimated to be 3 x 10 to the 12th/sq cm. 27 refs.

Interacting masers and the extreme brightness of astrophysical water masers

Extreme surface brightnesses have long been reported for water masers which are well beyond what is found in self-consistent, theoretical investigations of these masers. The transport of maser radiation is calculated when two masers, having the properties inferred for the numerous weaker masers and separated by distances characteristic of the molecular cloud, are aligned to within the angular spread of the beam of maser radiation. The beam size is reduced and brightness temperatures similar to the highest observed values are readily produced. This enhanced beaming reduces the number of photons required from each maser feature to a level that can be understood within available pumping scenarios. The large number of weaker masers that have been identified in the most luminous galactic cloud of water masers (the W49 region) makes it especially plausible that alignments occur and produce the very bright masers in this region.

A Biconically expanding flow in W43A traced by SiO maser emission

We report Very Long Baseline Array and Very Large Array observations of 22 GHz H2O and 43 GHz SiO (v = 1, J = 1-0) maser emission as well as 7 mm continuum emission in W43A, which exhibits a highly collimated jet of molecular gas and a spherically expanding envelope very similar to that of an OH/IR star. The spatiokinematical structure of the H2O masers is well fitted to a precessing jet model with an expansion velocity of 150 km s-1 and a dynamical age of ~50 yr. The spatiokinematical structure of the SiO masers is well fitted to a biconically expanding flow model, whose axis is parallel to the direction of the collimated jet. Astrometry of the H2O and SiO masers suggests that these maser sources have a common dynamical center, possibly as part of a binary system, within 70 AU. The SiO masers may be excited on the surface of the cone that has significant deceleration and interacts with the jet. A 7 mm continuum emission source is located ~1300 AU away from these maser sources at a position angle of about -60° from the jet axis. The physical relation of the continuum to the maser sources is still unclear.

Microstructure of Water Masers in W3 IRS 5

We report sub-milliarcsecond structures of water maser features in W3 IRS 5 observed with the Very Long Baseline Array (VLBA) at 22.2 GHz. A cluster of maser spots (emission spots in individual velocity channels) within a maser feature exhibits a simple velocity gradient but a complicated spatial alignment. Two-point spatial correlation functions for the spots can be fitted by power laws with an index of about 2 in both of the two ranges of 0.04-0.4 and 1-300 AU. This fact indicates a similar clustering of spots in the two very different ranges. The Doppler-velocity difference of the spots as a function of spot separation demonstrates a Kolmogorov-type turbulence in the range of 0.04-300 AU. Similar power laws in these functions have been reported for the W49N water masers. A unique difference of the W3 IRS 5 from the W49N masers is that on a scale above 1 AU, the Doppler-velocity difference of the spots in W3 IRS 5 (≤5 km s-1) is much smaller than that in W49N (≤150 km s-1). Very likely, this difference between the two sources arises because of different outflow velocities.

HIGH VELOCITY PRECESSING JETS FROM THE WATER FOUNTAIN IRAS 18286-0959 REVEALED BY VERY LONG BASELINE ARRAY OBSERVATIONS

We report the results of multi-epoch Very Long Baseline Array observations of the 22.2?GHz H2O maser emission associated with the water fountain IRAS?18286?0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by H2O maser emission, the other is W?43A. The detected H2O emission peaks are distributed over a velocity range from ?50?km?s?1 to 150?km?s?1. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest; the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a double-helix pattern which lies across ~200 mas. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The three-dimensional velocities of jet 1 and jet 2 are derived to be 138?km?s?1 and 99?km?s?1, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion.

SiO MASER SURVEY OF THE GALACTIC DISK IRAS SOURCES. I. 15¡ \ l \ 25¡, NEAR END OF THE GALACTIC BAR

A survey has been made in the SiO J = 1-0, v = 1 and 2 transitions (~43 GHz) for the color-selected IRAS sources in the Galactic disk area of 15? < l < 25? and |b| < 3? with the Nobeyama 45 m telescope. We have detected 67 out of 119 observed sources in SiO masers. Distances to the sources are deduced by the IRAS 12 and 25 ?m flux densities and range approximately from 2 to 12 kpc. The lines of sight of this region cross the location of the near end of the bar in the Galaxy. Radial velocities of the detected sources spread between -100 and 200 km s-1. This range slightly exceeds the possible limits expected from Galactic rotation. A comparison of the SiO with the CO and H I velocity-longitude (v-l) diagrams reveals that the overall distribution of the SiO maser sources on the v-l diagram resembles the molecular ring feature. Observational data are compared with the theoretical results of the bar models.

Molecular envelope of the planetary nebula NGC 7027

Strong emission of HCO(+) J = 1-0 has been detected in the molecular envelope of planetary nebula NGC 7027. A modeling of the envelope including a balance of thermal heating and cooling of the gas leads to a mass-loss rate of 0.0003 solar mass/yr, and the abundances of CO, HCO(+), and HCN of 0.0001, 3 x 10 to the -8th, and 0.9 x 10 to the -8th per H2, respectively. It is suggested that the large observed abundance of HCO(+) can be explained either by the ionization due to soft X-rays from the central star or a high gas-dust heat exchange rate. 44 refs.

SiO Maser Survey of the Galactic Disk IRAS Sources. II. |l| ≤ 3° and |b| ≤ 3°, the Galactic Center Area

A survey has been made in the SiO J = 1-0, v = 1 and 2 transitions (~43 GHz) for color-selected IRAS sources in the Galactic-center region of |l| ≤ 3° and |b| ≤ 3° using the Nobeyama 45 m telescope. We have detected 86 of 176 observed sources in the SiO masers. Distances to the sources are deduced from IRAS 12 and 25 μm flux densities and range approximately from 5 to 12 kpc. Radial velocities of the detected sources spread between -300 and 310 km s-1. The longitude-velocity (l-v) diagram exhibits an empty region of sources at l = -04-10 and Vlsr = 20-150 km s-1, which is interpreted as an undersampling effect of sources in the IRAS catalog at the Galactic central disk. The rotation rate, velocity dispersion, tilt angle of the rotation axis, and velocity shift at l = 0° are derived by fitting the velocities of the sources with a straight line as a function of Galactic longitude. These quantities are compatible with those obtained from previous observations of bulge stars with |b| > 3°. The average radial velocity of subsamples of stars tends to increase with distance, suggesting the presence streaming motion of stars in a barlike bulge. We conclude that most of the IRAS sources in the sample belong to the bulge.

Sio maser survey of the galactic disk IRAS sources. III. -10° <l<15° and | b | ≤3°, a central part of the Galaxy

A survey has been made in the SiO J = 1-0, v = 1 and 2 transitions (~43 GHz) for the color-selected IRAS sources in the central region of the Galaxy, -10? < l < 15? (except |l| ? 3?) and |b| ? 3?, with the Nobeyama 45 m telescope. We have detected 124 out of 200 observed sources in SiO masers. Distances to the sources range approximately from 2 to 11 kpc, if estimated from the IRAS 12 and 25 ?m flux densities. Radial velocities of the detected sources spread between ?260 km s-1. The distribution of SiO sources in the longitude-velocity diagram is compared with the H I contours. A number of sources are out of the H I limiting velocities; a group of negative-velocity (~-200 to -80 km s-1) sources is found at l = 3?-12? region. The subsamples of sources exhibit negative and positive shifts of the average radial velocity depending on distance, suggesting evidence of a streaming motion of stars in the bulge bar.