[en] Numerical solutions of three-dimensional, time-dependent coupled hydrodynamic equations for H₂O gas and dust are obtained in polar coordinates, in order to investigate the interaction between two cometary jets in the inner coma of an H₂O-dominated comet; both isolated and surrounded jet cases are treated. Shock waves consisting of two shock fronts and one compressed layer that is sandwiched between the two fronts are found to be formed in the region where the two cometary jets collide laterally, in three cases: (1) the isolated case of pure H₂O gas jets; (2) the surrounded case of pure H₂O gas jets with weak background ejection; and (3) the isolated case of dusty H₂O gas jets. 35 refs

[en] The bipolar outflow in NGC 2071 has been mapped in the CS (J = 2-1), CS (J = 1-0), HCO(+) (J = 1-0), and HCN (J = 1-0) lines, using the 45-m telescope of Nobeyama Radio Observatory with the narrow beams of HPBW = 20 arcsec and 40 arcsec. It is found that the rest components of the CS (J = 2-1) and CS (J = 1-0) lines have cavities at the centers of the red and blue lobes of the CO high-velocity emission, and that a single peak of the CS spectra outside the CO red lobe splits into two peaks inside the lobe. These features of the CS emission strongly suggest that the bipolar outflow in NGC 2071 consists of two expanding dense bubbles which are driven by a stellar wind from the IR cluster. The high-resolution mapping also reveals the fact that the CS bubbles have a clumpy structure. Two of the clumps are located at the place where the shocked H2 emission was detected. This fact indicates that formation of the strong shock results from the collision between the high-velocity wind from the IR cluster and the clumps in the ambient cloud. In addition, around the IR cluster this observation shows a disklike condensation, whose size is smaller than the width of the CO high-velocity outflow. 35 refs

[en] We present the results of C¹⁸O(J = 1-0) mapping observations of a 20' x 18' area in the Lynds 1204 molecular cloud associated with the Sharpless 2-140 (S140) H II region. The C¹⁸O cube (α-δ-v_LSR) data show that there are three clumps of sizes ∼1 pc in the region. Two of these have peculiar redshifted velocity components at their edges, which can be interpreted as the results of the interaction between the cloud and the Cepheus Bubble. From the C¹⁸O cube data, clumpfind identified 123 C¹⁸O cores, which have mean radius, velocity width in FWHM, and LTE mass of 0.36 ± 0.07 pc, 0.37 ± 0.09 km s^-1, and 41 ± 29 M_sun, respectively. Considering the uncertainty in the C¹⁸O abundance, all the cores in S140 are most likely to be gravitationally bound. We derived a C¹⁸O core mass function (CMF), which shows a power-law-like behavior above a turnover at 30 M_sun. The best-fit power-law index of -2.1 ± 0.2 is quite consistent with that of the initial mass function (IMF) and the C¹⁸O CMF in the OMC-1 region as found by Ikeda and Kitamura. Kramer et al. estimated the power-law index of -1.65 in S140 from the C¹⁸O(J = 2-1) data, which is inconsistent with this study. The C¹⁸O(J = 2-1) data are spatially limited to the central part of the cloud and are likely to be biased toward high-mass cores, leading to the flatter CMF. Consequently, this study and our previous study strongly support that the power-law form of the IMF has already been determined at the density of ∼< 10³-10⁴ cm^-3, traced by the C¹⁸O(J = 1-0) line.

[en] We have performed C¹⁸O (J = 1-0) mapping observations of a 20' x 20' area of the OMC-1 region in the Orion A cloud. We identified 65 C¹⁸O cores, which have a mean radius, a velocity width in FWHM, and an LTE mass of 0.18 ± 0.03 pc, 0.40 ± 0.15 km s^-1, and 7.2 ± 4.5 M _sun, respectively. All the cores are most likely to be gravitationally bound by considering the uncertainty in the C¹⁸O abundance. We derived a C¹⁸O core mass function, which shows a power-law-like behavior above 5 M _sun. The best-fit power-law index of -2.3 ± 0.3 is consistent with those of the dense core mass functions and the stellar initial mass function (IMF) previously derived in the OMC-1 region. This agreement strongly suggests that the power-law form of the IMF has been already determined at the density of ∼10³ cm^-3, traced by the C¹⁸O (J = 1-0) line. Consequently, we propose that the origin of the IMF should be searched in tenuous cloud structures with densities of less than 10³ cm^-3.

[en] We have carried out an H¹³CO⁺(J = 1 - 0) core survey in a large area of 1 deg², covering most of the dense region in the Orion B molecular cloud, using the Nobeyama 45 m radio telescope with the 25-BEam Array Receiver System. We cataloged 151 dense cores using the clumpfind method. The cores have mean radius, velocity width, and mass of 0.10 ± 0.02 pc, 0.53 ± 0.15 km s^-1, and 8.1 ± 6.4 M _sun, respectively, which are very similar to those in the Orion A cloud. We examined the spatial relation between our H¹³CO⁺ cores and the 850 μm cores observed by Johnstone and colleagues in 2001 and 2006, and found that there are two types of spatial relationships: H¹³CO⁺ cores with and without the 850 μm cores. Since the mean density of the 850 μm cores is higher than that of the H¹³CO⁺ cores, we can interpret the H¹³CO⁺ cores with 850 μm cores as being more centrally concentrated and hence more evolved, compared with those without. Considering the relationship between the masses of the H¹³CO⁺ and 850 μm cores, we estimate the 850 μm core mass function (CMF) using the H¹³CO⁺ CMF through the generalization of the confusion model proposed by Ikeda and colleagues in 2007. Our predicted 850 μm CMF is found to be quite consistent with that directly derived by Johnstone and colleagues. Furthermore, we predict the initial mass function (IMF) by the generalized confusion model assuming a star formation efficiency of 40% for the H¹³CO⁺ cores, and found that our predicted IMF is consistent with the Galactic field-averaged IMF within uncertainties. This agreement may indicate that the origin of the IMF goes back to the cloud structures with densities of less than 10⁴ cm^-3.

[en] We have carried out far-infrared imaging observations toward the Chamaeleon star-forming region by the Far-Infrared Surveyor (FIS) on board the AKARI satellite. The AKARI images cover a total area of 33.79 deg², corresponding to 210 pc² at the distance to the source. Using the FIS bands of 65-160 μm and the COBE/DIRBE bands of 60-240 μm, we constructed column density maps of cold (11.7 K) and warm (22.1 K) dust components with a linear resolution of 0.04 pc. On the basis of their spatial distributions and physical properties, we interpret that the cold component corresponds to the molecular clouds and the warm one the cold H I clouds, which are thought to be in a transient phase between atomic and molecular media. The warm component is shown to be uniformly distributed at a large spatial scale of ∼50 pc, while a several pc-scale gradient along the east-west direction is found in the distribution of the cold component. The former is consistent with a formation scenario of the cold H I clouds through the thermal instability in the warm neutral medium triggered by a 100 pc scale supernova explosion. This scenario, however, cannot produce the latter, several pc-scale gradient in molecular cloud mass. We conclude that the gravitational fragmentation of the cold H I cloud likely created the molecular clouds with spatial scale as small as several pc.

[en] Using the archive data of the H¹³CO⁺ (J = 1-0) line emission taken with the Nobeyama 45 m radio telescope with a spatial resolution of ∼ 0.01 pc, we have identified 68 dense cores in the central dense region of the ρ Ophiuchi main cloud. The H¹³CO⁺ data also indicate that the fractional abundance of H¹³CO⁺ relative to H₂ is roughly inversely proportional to the square root of the H₂ column density with a mean of 1.72 x 10^-11. The mean radius, FWHM line width, and LTE mass of the identified cores are estimated to be 0.045 ± 0.011 pc, 0.49 ± 0.14 km s^-1, and 3.4 ± 3.6 M_sun, respectively. The majority of the identified cores have subsonic internal motions. The virial ratio, the ratio of the virial mass to the LTE mass, tends to decrease with increasing LTE mass and about 60% of the cores have virial ratios smaller than 2, indicating that these cores are not transient structures but self-gravitating. The detailed virial analysis suggests that the surface pressure often dominates over the self-gravity and thus plays a crucial role in regulating core formation and evolution. By comparing the ρ Oph cores with those in the Orion A molecular cloud observed with the same telescope, we found that the statistical properties of the core physical quantities are similar between the two clouds if the effect of the different spatial resolutions is corrected. The line widths of the ρ Oph cores appear to be nearly independent of the core radii over the range of 0.01-0.1 pc and deviate upward from the Heyer and Brunt relation. This may be evidence that turbulent motions are driven by protostellar outflows in the cluster environment.

[en] We carried out an imaging survey of dust continuum emissions toward the Chamaeleon and Lupus regions. Observations were made with the 144-element bolometer array camera AzTEC mounted on the 10-meter sub-millimeter telescope ASTE during 2007-2008. The preliminary results of disk search and the cloud structure of Lupus III are presented.

[en] To study physical properties of the natal filament gas around the cloud core harboring an exceptionally young low-mass protostar GF 9-2, we carried out J = 1-0 line observations of ¹²CO, ¹³CO, and C¹⁸O molecules using the Nobeyama 45 m telescope. The mapping area covers ∼ one-fifth of the whole filament. Our ¹³CO and C¹⁸O maps clearly demonstrate that the core formed at the local density maxima of the filament, and the internal motions of the filament gas are totally governed by turbulence with Mach number of ∼2. We estimated the scale height of the filament to be H = 0.3-0.7 pc, yielding the central density of n _c = 800-4200 cm^–3. Our analysis adopting an isothermal cylinder model shows that the filament is supported by the turbulent and magnetic pressures against the radial and axial collapse due to self-gravity. Since both the dissipation timescales of the turbulence and the transverse magnetic fields can be comparable to the free-fall time of the filament gas of 10⁶ yr, we conclude that the local decay of the supersonic turbulence and magnetic fields made the filament gas locally unstable, hence making the core collapse. Furthermore, we newly detected a gas condensation with velocity width enhancement to ∼0.3 pc southwest of the GF 9-2 core. The condensation has a radius of ∼0.15 pc and an LTE mass of ∼5 M _☉. Its internal motion is turbulent with Mach number of ∼3, suggesting a gravitationally unbound state. Considering the uncertainties in our estimates, however, we propose that the condensation is a precursor of a cloud core, which would have been produced by the collision of the two gas components identified in the filament.

[en] In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (∼30-70 K), extended (radius of ∼2400 AU), dense (a few times 10⁵ cm^-3) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, 'warm-in-cold core stage (WICCS)', i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitute a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.