Jun-ichi Nakashima

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. 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.

Correlation between Infrared Colors and Intensity Ratios of SiO Maser Lines

We present the results of SiO millimeter line observations of a sample of known SiO maser sources covering a wide dust temperature range. A cold part of the sample was selected from the SiO maser sources found in our recent SiO maser survey of cold dusty objects. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. In particular, the correlation between infrared colors and SiO maser intensity ratio among the J = 1-0 v = 1, 2, and 3 lines are our main concern in this paper. We observed in total 75 SiO maser sources with the Nobeyama 45 m telescope quasi-simultaneously in the SiO J = 1-0 v = 0, 1, 2, 3, 4 and J = 2-1 v = 1, 2 lines. We also observed the sample in the 29SiO J = 1-0 v = 0 and J = 2-1 v = 0 lines, 30SiO J = 1-0 v = 0 line, and the H2O 61,6-52,3 line. As reported in previous papers, we confirmed that the intensity ratios of the SiO J = 1-0 v = 2 to v = 1 lines clearly correlate with infrared colors. In addition, we found possible correlation between infrared colors and the intensity ratios of the SiO J = 1-0 v = 3 to v = 1 and 2 lines. Two overlap lines of H2O (i.e., 116,6 ν2 = 1 → 127,5 ν2 = 0 and 50,5 ν2 = 2 → 63,4 ν2 = 1) might explain this correlation if these overlap lines become stronger with an increase of infrared colors, although the phenomena also might be explained in more fundamental ways if we take into account the variation of opacity from object to object.

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.

GASKAP-The Galactic ASKAP Survey

A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (H i) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of H i emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b| < 10°) at all declinations south of δ = +40°, spanning longitudes 167° through 360° to 79° at b = 0°, plus the entire area of the Magellanic Stream and Clouds, a total of 13 020 deg2. The brightness temperature sensitivity will be very good, typically σT≃ 1 K at resolution 30 arcsec and 1 km s−1. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream.

SiO maser survey of AGB stars in the North Galactic Cap

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

DISKLIKE STRUCTURE IN THE SEMIREGULAR PULSATING STAR X HERCULIS

This paper reports the results of a Berkeley-Illinois-Maryland (BIMA) array interferometric observation of a semiregular pulsating star with an unusual narrow molecular line profile, X Her, in the CO J = 1-0 line. In the CO spectrum, a double-component profile (including narrow and broad components) is seen, as reported by previous observations. The narrow component consists of two spiky peaks. The spatial structure of the board component shows bipolar shape, and that of the narrow component shows an elliptical/spherical shape. The two peaks in the narrow component show a systematic difference in the integrated intensity map. The kinematical and geometrical properties of the narrow component are reminiscent of a Keplerian rotating disk with a central mass of 0.9 M☉, although an interpretation as an expansion disk seems to be more natural. A secondary bipolar flow instead of the disk also cannot be fully excluded as an interpretation of the narrow line.

SiO Maser Survey of Cold IRAS Sources

We present the results of observations of cold IRAS sources in the Galactic disk area, 10 < l < 100 and jbj < 5 , in the SiO J = 1{0, v = 1 and 2 maser lines. SiO masers were detected in 51 out of 143 observed sources; 45 were new detections in SiO masers. The selected IRAS sources were objects with dust temperatures of between 160 and 280 K. According to a conrmation using 2MASS near-infrared images, a majority of the sample are AGB or post-AGB stars, although dense cores in the starforming regions (or dusty Hii regions) are involved in part of the sample. Among new detections, two were candidates for post-AGB stars: IRAS 18450 0148 (W 43A), and 19312+1950. We found that the intensity ratios of the SiO J = 1{0, v = 2 to the v = 1 line of the objects clearly correlate with those IRAS colors. The detection rates of SiO masers tend to increase toward the Galactic center as well as the cases of previous SiO maser surveys of typical AGB stars. No strong associations of the objects to the spiral arms were found. The radial-velocity dispersion of the present sample is comparable with the dispersion of the SiO maser sample of typical AGB stars. These facts suggest that the present sample of cold IRAS sources with SiO masers has a kinematic property very similar with that of typical AGB stars.

SiO Maser Survey of the Large-Amplitude Variables in the Galactic Center

We have surveyed ∼400 known large-amplitude variables within 15 ′ of the galactic center in the SiO J = 1–0 v = 1 and 2 maser lines at 43 GHz, resulting in 180 detections. SiO lines were also detected from 16 other sources, which are located within 20 ′′ (the telescope half beamwidth) of the program objects. The detection rate of 48 percent is comparable to that obtained in Bulge IRAS source surveys. Among the SiO detections, five stars have radial velocities greater than 200 km s −1 . The SiO detection rate increases steeply with the period of light variation, particularly for stars with P > 500 d, where it exceeds 80%. We found that, at a given period, the SiO detection rate is approximately three times that for OH. These facts suggest

SiO Maser Survey of IRAS Sources in the Inner Galactic Disk

We have surveyed 401 color selected IRAS sources in the Galactic disk in the SiO J=1--0 v= 1 and 2 maser lines at 43 GHz, resulting in 254 (239 new) detections. The observed sources lie mostly in a strip of the inner Galactic disk with boundaries -10<l<40 deg and |b|<3 deg. This survey provides radial velocities of inner-disk stars for which optical measurements cannot be made due to interstellar extinction. The SiO