Masato Ishiguro

New H2O masers in the NGC 7538 region

H2O maser emission in the NGC 7538 molecular cloud has been mapped with the Nobeyama Millimeter Array with absolute and relative positional accuracies of 0.5 arcsec and 0.2 arcsec, respectively. Five new masers have been found within an 8 arcmin x 8 arcmin area. One is associated with IRS 9, and the other four are not associated with any known infrared or optical sources. The brightest H{sub 2}O maser spot is 3 arcmin southwest from IRS 11 with a flux density of 156 Jy. These masers may be related to premain-sequence objects and/or protostars in the NGC 7538 molecular cloud. Two previously known H{sub 2}O masers associated with IRS 1-3 and IRS 11 are resolved into 11 and 12 maser spots, respectively. The H{sub 2}O maser spots associated with IRS 1-3 seem to be separated into two groups: one of which is very close to the ultracompact H II region at IRS 1, and the other far from IRS 1. 36 refs.

The Actual Dynamical Environment About Itokawa

The dynamical environment about and on Asteroid 25143 Itokawa is studied using the shape and rotation state model estimated during the close proximity phase of the Hayabusa mission to that asteroid. We first discuss the general gravitational properties of the shape model assuming a constant density. Next we discuss the actual dynamical environment about this body, both on the surface and in orbit, and consider the orbital dynamics of a Hayabusa-like spacecraft. Then we detail one of the approaches used to estimate the mass of the body, using optical and lidar imaging, during the close proximity phase.

Discovery of a rotating protoplanetary gas disk around the yound star GG Tauri

We have made aperture synthesis 12 CO(J=1-0) observations of a T Tauri star, GG Tau, in Taurus with 8″ resolution using the Nobeyama Millimeter Array (NMA). We have discovered a rotating gas disk having a radius of about 500 AU around GG Tau. The rotation velocity is 0.8 km s −1 /sin i at the radius, which is roughly consistent with a Kepler rotation around the central star. The inclination angle of the disk, i, is estimated to be about 60°, and the gas kinetic temperature is estimated to be about 8 K at that radius

Aperture synthesis observations of the molecular environment of the Sgr A complex. I. The M-0. 13-0. 08 molecular cloud

NH{sub 3} and H{sub 2}O maser observations of the 20 km/s molecular cloud M-0.13-0.08 in the Sgr A complex region are reported. NH{sub 3} (1,1) and (2,2) lines were observed simultaneously, and the molecular gas temperature and density are estimated. The NH{sub 3} emission is elongated in the same direction of the entire M-0.13-0.08 cloud and has a large velocity gradient along its major axis. Strong NH{sub 3} emission is located in the northern part of the cloud, where a perturbed velocity field and broad line widths are observed. In addition, a new H{sub 2}O maser spot was detected near one of the nonthermal continuum sources. These observational results suggest the physical association between a part of the M-0.13-0.08 molecular cloud and the nonthermal continuum sources in the Sgr A complex. 39 refs.

Landmark Navigation Studies and Target Characterization in the Hayabusa Encounter with Itokawa

On 12 September 2005, the Japanese Hayabusa spacecraft arrived at the asteroid 25143 Itokawa. Due to Itokawa’s small size (~550 meters) and low gravity, the spacecraft did not orbit, but hovered near each of two stations on a line between the asteroid and Earth. It remained at the “Gate Position” at a range of about 18 km until September 30, and then shifted to the “Home Position” at a range of about 7 km. Between October 8 and 28, it made several excursions to higher phase locations to obtain varying illumination conditions, and away from the equator to obtain polar data. On November 4, 9 and 12, the spacecraft made approaches to the asteroid in preparation for touchdowns on November 20 and 26.

A finger-like extension of the 20 kilometer per second cloud toward the Galactic center

High-resolution ammonia-line images of the M − 0.13 − 0.08 («20 km s −1 ») cloud in the Galactic center region have been obtained with the Nobeyama Millimeter Array. The 20 km s −1 cloud has a finger-like structure extending toward the Galactic center. It almost reaches to the circumnuclear ring (disk) surrounding Sgr A West in projection. A large systematic velocity gradient (5-10 km s −1 arcmin −1 ) along the elongation is found over the whole length of the cloud. We suggest that these characteristics are caused by tidal force in the gravitational field of the Galactic center.

Aperture synthesis observations of NH3 in OMC-1 : filamentary structures around Orion-KL

Aperture synthesis observations of the Orion molecular cloud 1 (OMC-1) have been made in NH{sub 3} (1, 1) and (2, 2) emission at 23.7 GHz, using the Nobeyama Millimeter Array (NMA), and obtained 16 arcsec resolution maps for OMC-1 and 8 arcsec resolution maps for the Orion-KL region. Filamentary structures extending over 0.5 pc from the Orion-KL region to the north and northwest directions were found. These structures are associated with the H2 finger structures and Herbig-Haro objects which are located at the blue-shifted side of the bipolar molecular outflow. The results suggest that these filaments are ambient molecular cloudlets with shocked surfaces caused by the strong stellar wind from the Orion-KL region. The 8 arcsec resolution NH{sub 3} (2, 2) maps show the extended features around the hot core of Orion-KL. These extended features correspond to the rotating disk and shocked shell associated with the bipolar molecular outflow. 37 refs.

Molecular gas bar and expanding molecular ring in the nucleus of the spiral galaxy Maffei 2

Aperture synthesis observations of the central 1.5 kpc region of the spiral galaxy Maffei 2 have been made in CO(J = 1-0) line. A central narrow ridge of molecular gas with a size 1000 pc x 200 pc and a ringlike feature with a large noncircular motion (60 km/s) with a size 500 pc x 240 pc have been found. The narrow ridge is interpreted as a bar of molecular gas in shocks generated at the leading edges in the bar potential. The observational results suggest that the ring is an expanding and rotating ring of molecular gas in the plane of the galaxy. The ring may have been formed by a starburst induced by the efficient gas supply in the bar potential. 38 refs.

High-resolution observations of CO from the bipolar nebula CRL 2688

The results of high spatial resolution mapping observations of CO emission from the bipolar nebula CRL 2688 are reported. The CO spectrum toward the center shows line wings with a full width of 85 km/s. On the blueshifted wing, a narrow and deep absorption feature is seen at a velocity shifted by 20 km/s from the systemic velocity. A central compact core elongated perpendicularly to the bipolar axis and blueshifted high-velocity emission distributed along the optical lobes suggest the presence of an expanding disk of molecular gas and fast stellar wind as the acceleration agent. The absorption feature suggests that an expanding cold absorbing envelope surrounds the relatively warm molecular envelope. The absorbing envelope has an excitation temperature lower than about 5 K and an optical depth larger than 1.2 in the CO(J = 1-0) line, and it is expanding at 20 km/s. The size of this envelope is larger than about 0.6 pc and its mass is larger than 0.016-0.044 solar mass. 16 references.

Ultra-Low Noise Photonic Local Oscillator at 100 GHz

Noise at millimeter wavelengths from a photonic local oscillator (LO) is compared with that from a Gunn oscillator using a low-noise superconductor-insulator-superconductor (SIS) receiver. No significant additional noise is added to the receiver by the photonic LO in the frequency range of 96–110 GHz.