Hiroyuki Maezawa

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)

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.

SUBMILLIMETER-WAVE C I SPECTRAL LINES FROM THE NGC 1333 REGION

We present large (30 × 40) maps in the C0 3P1-3P0 ([C I]; 492 GHz) and CO J = 3-2 (346 GHz) spectral lines of the NGC 1333 star-forming complex. We also report detections of the C0 3P2-3P1 (809 GHz) spectral line from 3 × 3 positions centered on HH 12. The overall extents of [C I] and CO J = 3-2 emission are similar to those of 13CO and C18O J = 1-0 emission. The CO J = 3-2 intensity peak is adjacent to the illuminating star SVS 3, while the [C I] intensity peaks at 5 southwest of the reflection nebula, filling a hollow surrounded by a -shaped dense molecular shell. We suggest that the observed [C I] distributions might be the result of nonequilibrium chemistry on the basis of the time-dependent chemical simulation. A huge expanding H I shell associated with the NGC 1333 cloud lends further support to this notion.

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 ...

Observation of the C I 3P2-3P1 Line toward the Orion Kleinmann-Low Region

The 3P2-3P1 fine-structure line of the neutral carbon atom (809 GHz) has been observed toward the Orion Kleinmann-Low (KL) region with the Mount Fuji submillimeter-wave telescope. The 6 × 6 area centered at Orion KL has been mapped with a grid spacing of 15. The intensity distribution of the 3P2-3P1 line is found to be similar to that of the 3P1-3P0 line; these lines are rather weak toward Orion KL, while they are both bright at Orion KLs northern and southern positions. The excitation temperature determined from the intensity ratio between the 3P2-3P1 and 3P1-3P0 lines ranges from 40 to 110 K. The excitation temperature is not enhanced toward Orion KL, whereas it tends to be high in the vicinity of θ1 Orionis C. These results indicate that the C I emission arises from a photodissociation surface illuminated by strong UV radiation from θ1 Ori C. The relative reduction in the C I intensities toward Orion KL is found to originate from a relatively low excitation temperature rather than from the depletion of the C I column density. The origin of the low-excitation temperature of C I toward Orion KL is discussed in terms of a radiative transfer effect.

Plan of receiver development for ASTE/LMSA

We present a plan of heterodyne receivers for Atacama Submillimeter Telescope Experiment (ASTE), which is one of Japanese R&D project of Large Millimeter Submillimeter Array (LMSA) and Atacama Large Millimeter Array (ALMA). A new 10 m submillimeter-wave telescope has been pre-installed at Nobeyama since February 2000 and will be installed at Pampa la Bola (el. 4800 m) in northern Chile. The telescope has four receiver layouts: (1) A shaped Cassegrain optics was designed for the Nobeyama operation to achieve high beam-efficiency at millimeter-wave bands. (2) Normal Gaussian optics will be replaced for the Chile operation to optimize submillimeter- wave bands up to 850 GHz. (3) It is possible to install an ALMA prototype receiver at the focus of secondary reflector. (4) An optics for submillimeter SIS photon camera. We describe the 350 GHz receiver which noise temperature was around 55 K in the frequency band of 330 - 360 GHz. The temperature ripple at the 4 K stage of two stages Gifford-McMahon refrigerator has been reduced to be less than 10 mK by employing a He-pot temperature stabilizer.

Large-Scale Mapping Observations of the C i (3P1–3P0) and CO (J = 3–2) Lines toward the Orion A Molecular Cloud

Large-scale mapping observations of the 3P1-3P0 fine-structure transition of atomic carbon (C i, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C i emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (J=1-0). The CO (J=3-2) emission shows a more featureless and extended distribution than C i. The C i/CO (J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C i/13CO (J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C i and 13CO (J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.