We present the results of an imaging survey of protoplanetary disks around single T Tauri stars in Taurus. Thermal emission at 2 mm from dust in the disks has been imaged with a maximum spatial resolution of 1'' by using the Nobeyama Millimeter Array. Disk images have been successfully obtained under almost uniform conditions for 13 T Tauri stars, two of which are thought to be embedded. We have derived the disk properties of outer radius, surface density distribution, mass, temperature distribution, and dust opacity coefficient, by analyzing both our images and the spectral energy distributions on the basis of two disk models: the usual power-law model and the standard model for viscous accretion disks. By examining correlations between the disk properties and disk clocks, we have found radial expansion of the disks with decreasing H? line luminosity, a measure of disk evolution. This expansion can be interpreted as radial expansion of accretion disks due to outward transport of angular momentum with evolution. The increasing rate of the disk radius suggests that the viscosity has weak dependence on radius r and ? ~ 0.01 for the ? parameterization of the viscosity. The power-law index p of the surface density distribution [?(r) = ?0(r/r0)-p] is 0-1 in most cases, which is smaller than 1.5 adopted in the Hayashi model for the origin of our solar system, while the surface density at 100 AU is 0.1-10 g cm-2, which is consistent with the extrapolated value in the Hayashi model. These facts may imply that in the disks of our sample it is very difficult to make planets like ours without redistribution of solids, if such low values for p hold even in the innermost regions.

https://iopscience.iop.org/article/10.1086/344223/pdf

Investigation of the Physical Properties of Protoplanetary Disks around T Tauri Stars by a 1 Arcsecond Imaging Survey: Evolution and Diversity of the Disks in Their Accretion Stage*

ASTE (Atacama Submillimeter Telescope Experiment) is a project to install and operate a 10-m submillimeter telescope in the high altitude site (4,800 m) in Atacama desert, northern Chile. The project is aimed to explore the southern sky with submillimeter waves as well as to develop and evaluate various instruments and observing techniques. The telescope was shipped and re-assembled in Chilean site in early 2002, including the establishment of the on site infrastructure. Following evaluation of the telescope and receivers, scientific observations such as supernova remnants, galaxies, star forming regions and proto-planetary nebulae, have been carried out since early 2003. The high-precision 10-m antenna was measured to have the surface accuracy of 18.9 mm and the relative pointing accuracy was 1.2" r.m.s. for both azimuth and elevation. The subreflector is equipped with wobbling capability. Several types of receivers have been on board the telescope; the heterodyne-receivers operating at 100, 230, 345, 500 and 800 GHz bands including cartridge-type receivers, as well as a bolometer system covering 350, 650 and 850 GHz. The spectrometer is equipped with an XF type digital auto-correlator with four channels each covering up to 512 MHz with 1024 bins, which leads to 2 GHz coverage. The control system is designed to be capable of remote control from several sites via network connection, from the base facility at San Pedro de Atacama (2,400 m altitude) or even from Japan.

The Atacama Submillimeter Telescope Experiment (ASTE)

The data from a CO(1 - 0) mapping survey of 40 nearby spiral galaxies performed with the Nobeyama 45-m telescope are presented. The criteria of the sample selection were (1) RC3 morphological type in the range Sa to Scd, (2) distance less than 25 Mpc, (3) inclination angle less than 79deg (RC3), (4) flux at 100 um higher than ~ 10 Jy, (5) spiral structure is not destroyed by interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bar on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of central concentration is higher in barred spirals than in non-barred spirals as shown by the previous works. Furthermore, we present an observational evidence that bars are efficient in driving molecular gas that lies within the bar length toward the center, while the role in bringing gas in from the outer parts of the disks is small. The transported gas accounts for about half of molecular gas within the central region in barred spiral galaxies. We found a correlation between the degree of central concentration and bar strength. Galaxies with stronger bars tend to have higher central concentration. The correlation implies that stronger bars accumulate molecular gas toward the center more efficiently. These results are consistent with long-lived bars.

/pdf/nobeyama-co-atlas-of-nearby-spiral-galaxies-distribution-of-12ut84ez69.pdf

Nobeyama CO Atlas of Nearby Spiral Galaxies: Distribution of Molecular Gas in Barred and Nonbarred Spiral Galaxies

We have developed a spectral line On-The-Fly (OTF) observing mode for the Nobeyama Radio Observatory 45-m and the Atacama Submillimeter Telescope Experiment 10-m telescopes. Sets of digital autocorrelation spectrometers are available for OTF with heterodyne receivers mounted on the telescopes, including the focal-plane 5
 $\times$ 
5 array receiver, BEARS, on the 45-m. During OTF observations, the antenna is continuously driven to cover the mapped region rapidly, resulting in a high observing efficiency and accuracy. Pointing of the antenna and readouts from the spectrometer are recorded as fast as 0.1s. In this paper we report on improvements made to the software and instruments, requirements and optimization of observing parameters, the data-reduction process, and verification of the system. It is confirmed that, using optimal parameters, the OTF is about twice as efficient as the conventional position-switch observing method.

/pdf/on-the-fly-observing-system-of-the-nobeyama-45-m-and-aste-10-al517hzdae.pdf

On-The-Fly Observing System of the Nobeyama 45-m and ASTE 10-m Telescopes

We present distributions of two molecular clouds having velocities of 2 and 14 km s{sup −1} toward RCW 38, the youngest super star cluster in the Milky Way, in the {sup 12}CO J = 1–0 and 3–2 and {sup 13}CO J = 1–0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3–2 emission to the J = 1–0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s{sup −1} cloud. We suggest that the collision is currently continuing toward part of the 2 km s{sup −1} cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud–cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way,more » holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.« less

http://iopscience.iop.org/article/10.3847/0004-637X/820/1/26/pdf

The two molecular clouds in rcw 38: evidence for the formation of the youngest super star cluster in the milky way triggered by cloud–cloud collision

New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.

Digital Spectrometers for the Nobeyama 45-m Telescope

We have developed 1-GHz bandwidth digital spectro-correlator system for the Nobeyama Millimeter Array (NMA). It consists of 2Gsample/sec-2bit analog-to-digital (A/D) converters and an ultra-wide band digital correlator. We developed two kinds of special-purpose LSI having functions of delay compensation and correlation, respectively. With these LSIs, the ultra-wide band digital correlator realizes 1024-MHz bandwidth spectroscopy with 128-channel resolution for 15-correlation data. This system allows us to observe radio continuum emission with about a two-times better signal-to-noise ratio than that of the previous correlator system. We started common-use observations with this new system from 1997 March; the system has been extended in order to obtain 21-correlation data for a 7-element "Rainbow" (NMA + 45-m telescope) interferometer system.

/pdf/1-ghz-bandwidth-digital-spectro-correlator-system-for-the-1gxyf1e32p.pdf

Atsushi Tanaka

Papers

Digital Spectrometers for the Nobeyama 45-m Telescope

1-GHz Bandwidth Digital Spectro-Correlator System for the Nobeyama Millimeter Array