KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis Major star-forming region

In observational studies of infrared dark clouds, the number of detections of CO freeze-out onto dust grains (CO depletion) at pc-scale is extremely limited, and the conditions for its occurrence are, therefore, still unknown. We report a new object where pc-scale CO depletion is expected. As a part of Kagoshima Galactic Object survey with Nobeyama 45-m telescope by Mapping in Ammonia lines (KAGONMA), we have made mapping observations of NH3 inversion transition lines towards the star-forming region associated with the CMa OB1 including IRAS 07077-1026, IRAS 07081-1028, and PGCC G224.28-0.82. By comparing the spatial distributions of the NH3 (1,1) and C18O (J=1-0), an intensity anti-correlation was found in IRAS 07077-1026 and IRAS 07081-1028 on the ~1 pc scale. Furthermore, we obtained a lower abundance of C18O at least in IRAS 07077-1026 than in the other parts of the star-forming region. After examining high density gas dissipation, photodissociation, and CO depletion, we concluded that the intensity anti-correlation in IRAS 07077-1026 is due to CO depletion. On the other hand, in the vicinity of the centre of PGCC G224.28-0.82, the emission line intensities of both the NH3 (1,1) and C18O (J=1-0) were strongly detected, although the gas temperature and density were similar to IRAS 07077-1026. This indicates that there are situations where C18O (J=1-0) cannot trace dense gas on the pc scale and implies that the conditional differences that C18O (J=1-0) can and cannot trace dense gas are unclear.Comment: 19 pages, 15 figures, 4 tables, accepted for Publications of the Astronomical Society of Japan (PASJ). The version 1 is the Author's Original Version. My accepted manuscript will be publicly available on the arXiv one year after publication in the PAS

Multi log-normal density structure in Cygnus-X molecular clouds: A fitting for N-PDF without power-law

We studied the H$_2$ column density probability distribution function (N-PDF) based on molecular emission lines using the Nobeyama 45-m Cygnus X CO survey data. Using the DENDROGRAM and SCIMES algorithms, we identified 124 molecular clouds in the $^{13}$CO data. From these identified molecular clouds, an N-PDF was constructed for 11 molecular clouds with an extent of more than 0.4 deg$^2$. From the fitting of the N-PDF, we found that the N-PDF could be well-fitted with one or two log-normal distributions. These fitting results provided an alternative density structure for molecular clouds from a conventional picture. We investigated the column density, dense molecular cloud cores, and radio continuum source distributions in each cloud and found that the N-PDF shape was less correlated with the star-forming activity over a whole cloud. Furthermore, we found that the log-normal N-PDF parameters obtained from the fitting showed two impressive features. First, the log-normal distribution at the low-density part had the same mean column density ($\sim$ 10$^{21.5}$ cm$^{-2}$) for almost all the molecular clouds. Second, the width of the log-normal distribution tended to decrease with an increasing mean density of the structures. These correlations suggest that the shape of the N-PDF reflects the relationship between the density and turbulent structure of the whole molecular cloud but is less affected by star-forming activities.Comment: 14 pages, 7 Figures, Accepted in MNRA

Ammonia mapping observations of the Galactic infrared bubble N49: Three NH3_3 clumps along the molecular filament

We have carried out the NH$_3$ $(J,K)=(1,1),(2,2),$ and $(3,3)$ mapping observations toward the Galactic infrared bubble N49 (G28.83-0.25) using the Nobeyama 45 m telescope. Three NH$_3$ clumps (A, B, and C) were discovered along the molecular filament with the radial velocities of $\sim$ 96, 87, and 89 km s$^{-1}$, respectively. The kinetic temperature derived from the NH$_3$ (2,2)/NH$_3$ (1,1) shows $T_{\rm kin} = 27.0 \pm 0.6$ K enhanced at Clump B in the eastern edge of the bubble, where position coincides with massive young stellar objects (MYSOs) associated with the 6.7 GHz class II methanol maser source. This result shows the dense clump is locally heated by stellar feedback from the embedded MYSOs. The NH$_3$ Clump B also exists at the 88 km s$^{-1}$ and 95 km s$^{-1}$ molecular filament intersection. We therefore suggest that the NH$_3$ dense gas formation in Clump B can be explained by a filament-filament interaction scenario. On the other hand, NH$_3$ Clump A and C at the northern and southern side of the molecular filament might be the sites of spontaneous star formation because these clumps are located $\sim$5$-$10 pc away from the edge of the bubble.Comment: 29 pages, 13 figures, 3 tables, accepted for Publications of the Astronomical Society of Japan (PASJ

Maintainability of the Helical Reactor FFHR-c1 Equipped with the Liquid Metal Divertor and Cartridge-type Blankets

The maintenance scheme in the compact helical fusion reactor, FFHR-c1, equipped with the liquid metal divertor, REVOLVER-D (Reactor-oriented Effectively VOLumetric VERtical Divertor) and the cartridge-type molten salt blankets, CARDISTRY-B (CARtridges Divided and InSerTed RadiallY − Blanket), is investigated. The magnetic configuration of the compact variant FFHR-c1 is similar to that of the Large Helical Device (LHD), while the device size is 2.8 times enlarged from LHD and a strong magnetic field strength of ∼8 T at the plasma center is adopted. The maintenance of the REVOLVER-D is simpler than that of the helical divertor with a complicated structure as seen in the LHD. In the REVOLVER-D, showers of molten tin are injected into the ergodic layer at 10 inner ports. To circulate the molten tin, 10 sets of the shower system including a liquid metal pump, ducts, a showerhead, a pool, and a heat exchanger, are installed. These can be replaced with simple up/down motions. The CARDISTRY-B consists of 320 tritium breeding blanket cartridges, which are toroidally segmented every two degrees. These cartridges are maintained by using heavy manipulators with a simple 4DOF motion at a constant toroidal angle

Conceptual design of a liquid metal limiter/divertor system for the FFHR-d1

A new liquid metal divertor system named the REVOLVER-D (Reactor-oriented Effectively VOLumetric VERtical Divertor) is proposed for the helical fusion reactor FFHR-d1. The REVOLVER-D is composed of molten tin shower jets stabilized by internal flow resistances of wire/tape/chain. These shower jets are inserted into the ergodic layer surrounding the main plasma. Tin is selected as the liquid metal because of its low melting point, low vapor pressure, low material cost, and high safety. The liquid metal pumps, cryopumps, and turbo molecular pumps are installed in the central vacuum vessel connected to the main vacuum vessel via 10 inner ports equipped with maze neutron shields. Central solenoid coils made of high-temperature superconductors are installed inside the central vacuum vessel to shield the pumps from the strong magnetic field. The REVOLVER-D has a good possibility to satisfy important characteristics required for the divertor system in a fusion reactor, that is, high heat load tolerance, high maintainability, sufficient vacuum pump speed, high level of safety, and a small amount of radioactive wastes

Estimation of the restitution coefficient by strain measurement

In order to clarify the collision phenomenon of the traffic machine in motion, such as automobile and aircraft, it is necessary to examine not only the deformation and the behavior of composed structural member but also the dynamic characteristic of friction coefficient and restitution coefficient in the collided contact surface. In this study, the restitution coefficient was estimated from the strain waveform measured by collision test using the Air Gun. The velocity and deformation dependence of the restitution coefficient was examined by carrying out the collision test at the different speed. As a result, in the metal test piece, restitution coefficient decreased by the plastic deformation with the increasing of the collision speed, and the velocity dependence was confirmed