Tomofumi Umemoto

Molecular cloud cores in the Orion A cloud. I: Nobeyama CS (1-0) survey

A first high-resolution survey of molecular cloud cores in the Orion A giant molecular cloud is reported. We identified 125 molecular cloud cores from an analysis of the spatial and velocity distribution of the CS (1-0) emission. The cores are generally elongated along the filamentary molecular cloud, and the axial ratio is about 0.5. The mass spectrum index of the cores is -1.6 for M≥50 M ○ .. The physical properties of the cores identified in Orion are compared with those of cores in dark clouds reported in the literature. The average radius of the cores in the Orion A cloud, 0.16 pc, is comparable to that of the cores in dark clouds

Detection of SiO emission in the L1157 dark cloud

Intense thermal emission lines of SiO (v = 0, J = 1-0 and 2-1) are detected in a low-mass star-forming region, L1157. The emission is confined to a compact region toward the blue lobe of the CO outflow, where shock heating due to interaction between the outflow and dense gas has been found. In contrast, the emission of SiO is not detected toward the IRAS source and the red lobe. The distribution of SiO is different from that of CS; the intense CS line is observed in the vicinity of the IRAS source. The peak fractional abundance of SiO is estimated to be about 10 -7

The outflow in the L1157 dark cloud - Evidence for shock heating of the interacting gas

In the L1157 dark cloud, a well-collimated bipolar CO outflow associated with a cold IRAS source 20386+6751 have been discovered. The gas kinetic temperature toward the blue lobe of the outflow rises to-30 K from the temperature of the surrounding gas (≤10 K); this high temperature region is very localized with the blue lobe. The HCO + , HCN, and NH3 lines show blueshifted and broad-line profiles toward the blue CO lobe. Furthermore, their distributions are similar to that of the blue lobe

The Ortho-to-Para Ratio of Ammonia in the L1157 Outflow*

We have measured the ortho-to-para ratio of ammonia in the blueshifted gas of the L1157 outflow by observing the six metastable inversion lines from &parl0;J,K&parr0;=&parl0;1,1&parr0; to (6, 6). The highly excited (5, 5) and (6, 6) lines were first detected in the low-mass star-forming regions. The rotational temperature derived from the ratio of four transition lines from (3, 3) to (6, 6) is 130-140 K, suggesting that the blueshifted gas is heated by a factor of approximately 10 as compared to the quiescent gas. The ortho-to-para ratio of the NH3 molecules in the blueshifted gas is estimated to be 1.3-1.7, which is higher than the statistical equilibrium value. This ratio provides us with evidence that the NH3 molecules have been evaporated from dust grains with the formation temperature between 18 and 25 K. It is most likely that the NH3 molecules on dust grains have been released into the gas phase through the passage of strong shock waves produced by the outflow. Such a scenario is supported by the fact that the ammonia abundance in the blueshifted gas is enhanced by a factor of approximately 5 with respect to the dense quiescent gas.

Effects of magnetic fields and rotation on the fragmentation of filamentary molecular clouds - Comparison of the theory with the Orion A cloud

We discuss the fragmentation of a filamentary molecular cloud on the basis of a magnetohydrodynamical stability analysis and the observations of the Orion A cloud with the Nobeyama 45 m telescope. Our model cloud has axial and helical magnetic fields and rotates around the axis. The dispersion relation for this cloud shows that the presence of a magnetic field and/or rotation shortens the wavelength of the most unstable mode, i.e., the mean distance between the adjacent fragments, measured in units of the filament diameter. We compare the theoretical results with the observed clumpy structure of the filamentary Orion A cloud and find that the sum of magnetic and centrifugal forces in the parent cloud was comparable with the pressure force (thermal and turbulent) and has had significant effects on the fragmentation

THE MOLECULAR OUTFLOWS IN THE {rho} OPHIUCHI MAIN CLOUD: IMPLICATIONS FOR TURBULENCE GENERATION

We present the results of CO (J = 3 – 2) and CO (J = 1 – 0) mapping observations toward the active cluster-forming clump, L1688, in the ρ Ophiuchi molecular cloud. From the CO (J = 3 – 2) and CO (J = 1 – 0) data cubes, we identify five outflows, whose driving sources are VLA 1623, EL 32, LFAM 26, EL 29, and IRS 44. Among the identified outflows, the most luminous outflow is the one from the prototypical Class 0 source, VLA 1623. We also discover that the EL 32 outflow located in the Oph B2 region has very extended blueshifted and redshifted lobes with wide opening angles. This outflow is most massive and has the largest momentum among the identified outflows in the CO (J = 1 – 0) map. We estimate the total energy injection rate due to the molecular outflows identified by the present and previous studies to be about 0.2 L ☉, larger than or at least comparable to the turbulence dissipation rate [≈(0.03 – 0.1)L ☉]. Therefore, we conclude that the protostellar outflows are likely to play a significant role in replenishing the supersonic turbulence in this clump.

Molecular Outflows from X-Ray-Emitting Protostars in the ρ Ophiuchi Dark Cloud

We report CO (J = 2-1, J = 1-0) outflows from four X-ray-emitting protostars (EL29, IRS44, WL6, WL10) in the ρ Ophiuchi cloud core which have been firmly identified with the X-ray satellite ASCA. The common feature of these outflows is that the blue and red lobes are largely overlapped, which indicates that the inclination angle between the outflow axis and line of sight is smaller than 30° (nearly pole-on configuration). Taking account of the hard X-ray transparency (NH ~ 1023 cm-2) and the column density of a circumstellar disk (NH > 1024 cm-2), it is naturally understood that hard X-rays emitted near the surface of protostars or the inner part of the disk are observed in the nearly pole-on configuration. The outflow detection rate (4/5) in the present observations shows that a low-mass protostar emits X-rays even in the outflow phase of early stellar evolution.

Bipolar outflow in B335 : the small-scale structure

Interferometric observations of the 12 CO (J=1-0) and 2.6 mm continuum emission toward the young stellar object in B335 are presented. The angular resolution of 8″ × 5″ is a factor of 3 higher than those of the previous single-dish observations. The 12 CO high-velocity emission shows distinct biconical outflow structure having a size of a few thousand AU. The north-south extent of the outflow at its center is smaller than our present beam size, indicating that the outflow is focused within ∼1000 AU of its origin

Molecular Outflow Search in the ρ Ophiuchi A and B2 Regions

We have searched for CO molecular outflows associated with the cloud A and B2 of the ρ Ophiuchi star-forming region. On the basis of single -dish 12CO (J = 3-2) and interferometric 12CO (J = 1-0) observations, we have identified three molecular outflows in the ρ Oph A cloud and one in the ρ Oph B2 cloud. Out of the four outflows observed in these regions, one is the known outflow driven by the Class 0 source, VLA 1623, and the other three are newly discovered ones. The inclination and opacity corrected momentum flux FCO of newly detected outflows are roughly comparable to those of Class I objects observed by Bontemps et al. (1996). All the newly discovered outflows are likely to be driven by Class II sources or near-infrared sources, and none of them is associated with the cold submillimeter-millimeter sources without infrared counter parts. These results indicate that protostars associated with outflows whose mass and momentum flux exceed our detection limit are not formed yet in the high-density ridge of the ρ Oph A region and the northeastern condensation in the ρ Oph B2 region, suggesting that they are considered to be pre-protostellar cores.

The Powering Source and Origin of the Quadrupolar Molecular Outflow in L723

We present the results of single-dish observations of CS J = 2-1 and J = 3-2 and interferometric observations of CO J = 1-0 toward the center of the quadrupolar molecular outflow in L723. We have detected a compact CS condensation having a size of 0.04 pc and a mass of 0.55 M? toward the northeastern radio continuum source VLA 2 (AER91 2). The CO outflow also shows the distribution centered at VLA 2. These results suggest that the source VLA 2 is the young stellar object that is powering the conspicuous molecular outflow system. On the other hand, there is no enhancement in the CS intensity or the CO outflow distribution toward the southwestern radio continuum source VLA 1 (AER91 1), indicating that the source VLA 1 does not contribute to the morphology of the quadrupolar outflow in L723. The CO distribution observed with the interferometer delineates the western edge of the blue lobe and the northeastern edge of the red lobe revealed in the single-dish map, suggesting that the outflow in L723 is a single bipolar outflow with a wide opening angle of 120?-170? rather than two independent outflows. We found signs of interaction between the blueshifted outflow and the dense ambient gas: (1) there is a compact CS clump blueshifted by ~1 km s-1, the distribution of which shows anticorrelation with the blueshifted CO outflow; (2) both CS and NH3 spectra show the line broadening toward the blueshifted clump; and (3) there is a temperature enhancement at the boundary of the blueshifted clump of CS emission. It is likely that such interaction with the dense ambient gas has the increased opening angle of the outflow, which accounts for the quadrupolar morphology.