Publications (4)12.05 Total impact
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Article: CH radio emission from heiles cloud 2 as a tracer of molecular cloud evolution
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ABSTRACT: A mapping observation of the $J=1/2$ $\Lambda$-type doubling transition (3.3 GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus molecular cloud complex to reveal its molecular cloud-scale distribution. The observations were carried out with the Effelsberg 100 m telescope. The CH emission is found to be extended over the whole region of HCL2. It is brighter in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in the northwestern part. Its distribution extends continuously from the peak of the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were connecting the distributions of the [C I] and C$^{18}$O emissions. Since CH is an intermediate in gas-phase chemical reactions from C to CO, its emission should trace the transition region. The above distribution of the CH emission is consistent with this chemical behavior. Since the CH abundance is subject to the chemical evolutionary effect, the CH column density in HCL2 no longer follows a linear correlation wit the H$_2$ column density reported for diffuse and translucent clouds. More importantly, the CH line profile is found to be composed of the narrow and broad components. Although the broad component is dominant around the CI peak, the narrow component appears in the TMC-1 ridge and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a narrowing of the line width during the formation of dense cores. These results suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and physical evolution of molecular clouds.09/2012; -
Article: Distribution of the CI Emission in the Rho Ophiuchi Dark Cloud
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ABSTRACT: The 3P1-3P0 fine-structure line of the neutral carbon atom ([C I]) has been mapped over the 1.8d×1.3d 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 Astrophysical Journal 05/2003; 589(1):378-385. · 6.02 Impact Factor -
Article: Atomic Carbon and CO Isotope Emission in the Vicinity of DR15
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ABSTRACT: We present observations of the 3P1-3P0 fine structure transition of atomic carbon [CI], the J=3-2 transition of CO, as well as of the J=1-0 transitions of 13CO and C18O toward DR15, an HII region associated with two mid-infrared dark clouds (IRDCs). The 13CO and C18O J=1-0 emissions closely follow the dark patches seen in optical wavelength, showing two self-gravitating molecular cores with masses of 2000 Msun and 900 Msun, respectively, at the positions of the catalogued IRDCs. Our data show a rough spatial correlation between [CI] and 13CO J=1-0. Bright [CI] emission occurs in relatively cold gas behind the molecular cores, neither in highly excited gas traced by CO J=3-2 emission nor in HII region/molecular cloud interface. These results are inconsistent with those predicted by standard photodissociation region (PDR) models, suggesting an origin for interstellar atomic carbon unrelated to photodissociation processes. Comment: 11 pages Latex, 6 figures, Accepted for publication in The Astrophysical Journal05/2001; -
Article: Observation of the CI 3P2-3P1 Line Toward the Orion Kleinmann-Low Region
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ABSTRACT: 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 1.5′. 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 KL's 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.The Astrophysical Journal 02/2001; 547(2):L165-L169. · 6.02 Impact Factor
