Masafumi Ikeda

Large-scale mapping observations of the CI 3P1-3P0 line toward heiles cloud2 in the Taurus Dark Cloud

A distribution of the neutral carbon atom (C i) in Heiles cloud 2 (HCL2) has been investigated with the Mount Fuji submillimeter-wave telescope. A region of 1.2 deg 2 covering a whole region of HCL2 has been mapped with the 3 P1‐ 3 P0 fine-structure line (492 GHz) of C i. The global extent of the C i emission is similar to that of 13 CO, extending from southeast to northwest. However, the C i intensity is found to be rather weak in dense cores traced by the line of C 18 O. On the other hand, strong C i emission is observed in a south part of J= 1‐0 HCL2 in which the C 18 O intensity is fairly weak. The C i/CO abundance ratio is greater than 0.8 for the C i peak, whereas it is 0.1 for the dense cores such as the cyanopolyyne peak. The C i‐rich cloud found in the south part may be in the early evolutionary stage of dense core formation where C i has not yet been converted completely into CO. This result implies that formation of dense cores is taking place from north to south in HCL2. Subject headings: ISM: atoms — ISM: clouds — ISM: evolution — ISM: individual (Heiles’s cloud 2)

Submillimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO

We have carried out submillimeter 12CO( -->J = 3?2) observations of six giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10 m submillimeter telescope at a spatial resolution of 5 pc and very high sensitivity. We have identified 32 molecular clumps in the GMCs and revealed significant details of the warm and dense molecular gas with -->n(H2) ~ 103?105 cm?3 and -->Tkin ~ 60 K. These data are combined with 12CO( -->J = 1?0) and 13CO( -->J = 1?0) results and compared with LVG calculations. The results indicate that clumps that we detected are distributed continuously from cool (~10-30 K) to warm (30-200 K), and warm clumps are distributed from less dense (~103 cm?3) to dense (~103.5-105 cm?3). We found that the ratio of 12CO( -->J = 3?2) to 12CO( -->J = 1?0) emission is sensitive to and is well correlated with the local H? flux. We infer that differences of clump properties represent an evolutionary sequence of GMCs in terms of density increase leading to star formation. Type I and II GMCs (starless GMCs and GMCs with H?II regions only, respectively) are at the young phase of star formation where density does not yet become high enough to show active star formation, and Type III GMCs (GMCs with H?II regions and young star clusters) represent the later phase where the average density is increased and the GMCs are forming massive stars. The high kinetic temperature correlated with H? flux suggests that FUV heating is dominant in the molecular gas of the LMC.

Production Pathways of CCS and CCCS Inferred from Their 13C Isotopic Species

The rotational spectral lines (JN = 32-21 and JN = 21-10) of 13CCS and C13CS have been observed toward a cold dark cloud, TMC-1. The strongest hyperfine component lines of 13CCS and C13CS (JN = 21-10, F = 5/2-3/2) have successfully been detected. The / abundance ratio is determined to be 4.2 ± 2.3 (3 σ). The / ratio is evaluated to be 230 ± 130 (3 σ), and hence, 13CCS is found to be significantly diluted. Such a difference between the 13CCS and C13CS abundances is also found in L1521E, which is a very young core with rich carbon-chain molecules. Therefore, the anomaly is not specific to TMC-1, but seems to be common for the CCS-rich clouds. Furthermore, we have also observed the J = 4-3 transition of 13CCCS and CCC34S in TMC-1 and L1521E and have found that the / ratio is larger than 8.4 (3 σ). This lower limit is considerably larger than the interstellar / ratio of 3, indicating that 13CCCS is diluted as in the case of 13CCS. These results give us strong constraints on the main pathways to produce CCS and CCCS.

The H13CN/HC15N Abundance Ratio in Dense Cores: Possible Source-to-Source Variation of Isotope Abundances?

We have observed the H13CN (J = 1-0) and HC15N (J = 1-0) lines simultaneously toward three dense cores in the Taurus molecular cloud complex and have found a significant source-to-source variation of the column density ratio, N(H13CN)/N(HC15N). The lowest ratio of 2.6-3.1 is observed toward L1521E, while the highest ratio of 8-11 is observed toward L1498. We have also observed the 12C18O (J = 1-0, 2-1) and 13C18O (J = 1-0) lines, and the 12C/13C ratio has been derived to be 58.8 ? 3.7 and ?117 toward L1521E and L1498, respectively. These results imply that a substantial isotope fractionation effect may exist in the formation processes of these molecules, or elemental abundances are not uniform among the observed sources. If the source-to-source variation of the (14N/15N)/(12C/13C) ratio in HCN and the 12C/13C ratio in CO originates from the elemental abundance variation, the 14N/15N ratio is calculated to be 151 ? 16 and ?813 for L1521E and L1498, respectively. These ratios significantly deviate from the values obtained toward Galactic disk sources.

Mapping Observations of DNC and HN13C in Dark Cloud Cores

We present results of mapping observations of the DNC, HN13C, and H13CO+ lines (J = 1-0) toward four nearby dark cloud cores, TMC-1, L1512, L1544, and L63, along with observations of the DNC and HN13C lines (J = 2-1) toward selected positions. By use of statistical equilibrium calculations based on the large velocity gradient (LVG) model, the H2 densities are derived to be ? 105 cm-3, and the [DNC]/[HN13C] ratios are derived to be 1.25-5.44, with a typical uncertainty of a factor of 2. The observed [DNC]/[HNC] ratios range from 0.02 to 0.09, assuming a [12C]/[13C] ratio of 60. Distributions of DNC and HN13C are generally similar to each other, whereas the distribution of H13CO+ is more extended than those of DNC and HN13C, indicating that they reside in a more inward part of the cores than HCO+. The [DNC]/[HN13C] ratio is rather constant within each core, although small systematic gradients are observed in TMC-1 and L63. In particular, no such systematic gradient is found in L1512 and L1544, where a significant effect of depletion of molecules is reported toward the central part of the cores. This suggests that the [DNC]/[HNC] ratio would not be very sensitive to the depletion factor, unlike the [DCO+]/[HCO+] ratio. On the other hand, the core-to-core variation of the [DNC]/[HNC] ratio, which ranges over an order of magnitude, is more remarkable than the variation within each core. These results are interpreted qualitatively by a combination of three competing time-dependent processes: gas-phase deuterium fractionation, depletion of molecules onto grain surfaces, and dynamical evolution of a core.

Atomic carbon and CO isotope emission in the vicinity of DR 15

We present observations of the P-3(1)-P-3(o) fine-structure transition of atomic carbon [C I], the J = 3-2 transition of CO, and the J = 1-0 transitions of (CO)-C-13 and (CO)-O-18 toward DR 15, an H II region associated with two mid-infrared dark clouds (IRDCs). The (CO)-C-13 and (CO)-O-18 J = 1-0 emissions closely follow the dark patches seen in optical wavelength, showing two self-gravitating molecular cores with masses of 2000 and 900 M-circle dot, respectively, at the positions of the cataloged IRDCs. Our data show a rough spatial correlation between [C I] and (CO)-C-13 J = 1-0. Bright [C I] emission occurs in the relatively cold gas behind the molecular cores but does not occur in either highly excited gas traced by CO J = 3-2 emission or in the H II region/molecular cloud interface. These results are inconsistent with those predicted by standard photodissociation region models, suggesting an origin for interstellar atomic carbon unrelated to photodissociation processes.

Distribution of the [C I] Emission in the ρ Ophiuchi Dark Cloud

The 3P1-3P0 fine-structure line of the neutral carbon atom ([C I]) has been mapped over the 18 × 13 area of the L1688 cloud in the ρ Ophiuchi region with the Mount Fuji submillimeter-wave telescope. The 3P2-3P1 line of [C I] has also been observed toward two representative positions to evaluate the excitation temperature of the [C I] lines. The overall extent of the [C I] distribution generally resembles that of the 13CO distribution. The [C I] distribution has two major peaks; one (peak I) is at ρ Oph A, and the other (peak II) is toward the east side of the C18O core in the southern part of L1688. Peak II is located beyond the C18O core with respect to the exciting star HD 147889. The C0 column density is 5.0 × 1017 cm-2 toward peak II. The spatial distribution of the [C I] emission is compared with plane-parallel photodissociation region (PDR) models, which suggest that peak II is associated with a lower density PDR front, adjacent to the dense cloud cores observed in the C18O line emission. Alternatively, peak II is in the early stage of chemical evolution, where C0 has not been completely converted to CO. In this case, the difference in the [C I] and C18O distributions represents an evolutionary sequence. This is consistent with a picture of a shock-compressed formation of the dense cores in this region due to influences from the Sco OB2 association.

The Mt. Fuji submillimeter-wave telescope

We have developed a 1.2 m submillimeter-wave telescope at the summit of Mt. Fuji to survey emission lines of the neutral carbon atom (CI) toward the Milky Way. A superconductor-insulator-superconductor mixer receiver on the Nasmyth focus is used to observe the 492 GHz band in SSB and the 345 GHz band in DSB simultaneously. The receiver noise temperature is 300 K in SSB and 200 K in DSB for 492 and 345 GHz, respectively. The intermediate frequency frequency is 1.8–2.5 GHz. An acousto-optical spectrometer which has the total bandwidth of 0.9 GHz and 1024 channel outputs has also been developed. The telescope was installed at the summit of Mt. Fuji (alt. 3725 m) in July 1998. It has been remotely operated via a satellite communication system from Tokyo or Nobeyama. Atmospheric opacity at Mt. Fuji was 0.4–1.0 at 492 GHz during 30% of the time and 0.07–0.5 at 345 GHz during 60% of the time from November 1998 to February 1999. The system noise temperature was 1000–3000 K in SSB at 492 GHz and 500–2000 K in DSB ...

Atomic carbon in the southern milky way

We present a coarsely sampled longitude-velocity (l-V) map of the region l = 300?-354?, b = 0? in the 492 GHz fine-structure transition of neutral atomic carbon (C0 3P1-3P0; [C I]), observed with the Portable 18 cm Submillimeter-wave Telescope (POST18). The l-V distribution of the [C I] emission resembles closely that of the CO J = 1-0 emission, showing a widespread distribution of atomic carbon on the Galactic scale. The ratio of the antenna temperatures, R, concentrates on the narrow range from 0.05 to 0.3. A large velocity gradient (LVG) analysis shows that the [C I] emission from the Galactic disk is dominated by a population of neutral gas with high C0/CO abundance ratios and moderate column densities, which can be categorized as diffuse translucent clouds. The ratio of bulk emissivity, J/JCO, shows a systematic trend, suggesting the bulk C0/CO abundance ratio increasing with the Galactic radius. A mechanism related to kiloparsec-scale structure of the Galaxy may control the bulk C0/CO abundance ratio in the Galactic disk. Two groups of high-ratio (R > 0.3) areas reside in the l-V loci several degrees inside of tangential points of the Galactic spiral arms. These could be gas condensations just accumulated in the potential well of spiral arms and be in the early stages of molecular cloud formation.

Measurement of absorption and charge exchange of

The combined cross section for absorption and charge exchange interactions of positively charged pions with carbon nuclei for the momentum range 200 MeV/c to 300 MeV/c have been measured with the DUET experiment at TRIUMF. The uncertainty is reduced by nearly half compared to previous experiments. This result will be a valuable input to existing models to constrain pion interactions with nuclei.