Naomi Hirano

Rotation in the Protostellar Envelopes around IRAS 04169+2702 and IRAS 04365+2535: The Size Scale for Dynamical Collapse

We report interferometric observations of two embedded protostar candidates, IRAS 04169+2702 and IRAS 04365+2535 (TMC-1A), in the Taurus molecular cloud. The C18O J = 1-0 emission from IRAS 04169+2702 reveals a flattened envelope 2200 AU × 1100 AU in size; there is a velocity gradient along the elongation axis, which in turn is perpendicular to the outflow direction. Since the rotational velocity corrected for inclination, 0.23 km s-1 at 370 AU, gives an unacceptably small dynamical mass of 0.02 M☉ within that radius, we speculate that there is additional radial motion, possibly infall, in the flattened envelope. Around IRAS 04365+2535, a compact 13CO J = 1-0 condensation ~1400 AU in size was detected. Again, the velocity gradient is perpendicular to the associated molecular outflow, but a rotation velocity of 0.87 km s-1 at 580 AU radius is consistent with the condensation being a rotationally supported disk. Combining our new data for the two sources with published observations of rotationally supported disks and infalling envelopes around five young stars associated with the Taurus molecular cloud enables us to compare local specific angular momenta of a significant sample of these sources on scales of 200-2000 AU with those of dense cores on 6000-80,000 AU (0.03-0.4 pc) scales. The specific angular momenta for infalling envelopes and rotationally supported disks are relatively constant, ~10-3 km s-1 pc, and are typically an order of magnitude smaller than those for dense cores. These results can be explained if the dynamical collapse of dense star-forming cores takes place inside radii of ~0.03 pc while the region outside this radius remains dynamically stable.

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.

The Initial Conditions for Formation of Low-Mass Stars: Kinematics and Density Structure of the Protostellar Envelope in B335

We have observed dense molecular gas toward a deeply embedded protostar in B335 using the Nobeyama 45 m telescope and the Nobeyama Millimeter Array. The H13CO+ and C18O maps taken by the 45 m telescope show elongated features perpendicular to the axis of molecular outflow, suggesting that these emission lines arise from a dense disklike envelope surrounding the protostar. The size and mass of the H13CO+ disklike envelope are 0.17 × 0.15 pc and 2.4 M☉, respectively. The C18O envelope gas has a linear velocity gradient along its major axis indicative of a rigid rotation with an angular velocity of 1.1 × 10-14 radians s-1. The density profile derived from the C18O and H13CO+ data shows a power law of ρ(r)~ρ0r-1.95~(a2/2πG)r-2 over the radius range between 0.03 and 0.2 pc. In addition, the coefficient of the density profile is consistent with Shus solution rather than Larsons, though there is uncertainty particularly in the fractional abundance of the H13CO+ molecule. Our results suggest that the protostar in B335 was formed in an isothermal core with a rigid rotation. The interferometric observations of the H13CO+ line reveal a dense compact feature centered on the protostar. This compact feature has a size of 2000 AU, and its elongation is roughly perpendicular to the outflow axis. We thus consider that this compact feature is an inner part of the disklike envelope. There is a velocity gradient along the minor axis of the feature which might be interpreted as a disk infalling motion. The previous observations also suggested the existence of infalling motion toward the protostar B335 IRS. In addition, the inner envelope shows a rotating motion of Vθ=0.14 km s-1 at r=490 AU. This rotational velocity is smaller than the corresponding Keplerian velocity of ~0.42 km s-1, indicating that the inner envelope is not rotationally supported.

A Comparison of the Spatial Distribution of H13CO+, CH3OH, and C34S Emission and Its Implication in Heiles Cloud 2

We have mapped the Heiles cloud 2 region in the Taurus molecular cloud complex with H13CO+ (J = 1-0), CH3OH (JK = 20-10 A+), and C34S (J = 2-1) lines. Dense gas traced by the mapped lines with critical densities higher than 104 cm-3 is concentrated in four condensations, that is, the TMC 1 and TMC 1C filaments, L1527, and TMC 1A. We have found that the three emission lines have remarkably different spatial distributions. The H13CO+ emission traces well dense cores harboring protostars, while the CH3OH emission is weak toward the protostars and is rather enhanced toward cores without protostars. We found that there are two starless cores with enhanced CH3OH emission at the northwestern ends of the TMC 1 and TMC 1C filaments, toward which the H13CO+ emission is barely seen. On the basis of the analyses using the large velocity gradient (LVG) model, we show that the CH3OH abundance relative to H13CO+ is enhanced by up to 1 order of magnitude in the cores without protostars. The C34S abundance relative to H13CO+ also shows a similar trend to that of CH3OH. Such an abundance variation between H13CO+ and CH3OH and C34S can be explained in the scheme of time-dependent gas-phase chemical evolution, which predicts that CH3OH and C34S are abundant in the early stages of chemical evolution and become deficient in the later stages. A comparison of the spatial-velocity structures in TMC 1 observed with the three molecular lines suggests that this cloud consists of multiple components with different velocities and different chemical compositions along the line of sight.

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.

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.

Molecular Cloud Cores in the Orion A Cloud. II. FCRAO CS (2-1) Data

CS (2-1) data of the Orion A Cloud obtained with the FCRAO 14 m telescope are shown. The CS (2-1) image shows the clumpy and filamentary structure of the Orion A cloud, as did our previous CS (1-0) image, obtained with the NRO 45 m telescope. The peak intensity TMB (CS 2-1) decreases more steeply than TMB (CS 1-0) toward the south along the filament. It is found that the gas density of the CS cores tends to be lower in the south of the cloud, and this explains the above difference in the line-intensity decrease. From CS and C34S data, we estimated the optical depth of CS (2-1) to be moderately high (2-5) and that of CS (1-0) to be typically less than unity.

Expanding molecular torus around the planetary nebula IRAS 21282 + 5050

The CO (J = 1-0) emission at 115.271 GHz from the compact planetary nebula IRAS 21282 + 5050 has been mapped. The results suggest that the CO gas forms an expanding torus with an axis along the east-west direction, normal to the line of sight. The kinematical age of the torus is estimated at about 21,000 D yr, where D is the distance to IRAS 21282 + 5050 in kpc. It is concluded that IRAS 21282 + 5050 is in earlier evolutionary stage of planetary nebular than NGC 7027 and NGC 2346. 20 refs.

Planck Cold Clumps in the λ Orionis Complex. II. Environmental Effects on Core Formation

Based on the 850 μm dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the λ Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well-known active star-forming regions, while the λ Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant H II region. PGCCs in the λ Orionis cloud have higher dust temperatures (T d = 16.13 ± 0.15 K) and lower values of dust emissivity spectral index (β = 1.65 ± 0.02) than PGCCs in the Orion A (T d = 13.79 ± 0.21 K, β = 2.07 ± 0.03) and Orion B (T d = 13.82 ± 0.19 K, β = 1.96 ± 0.02) clouds. We find 119 substructures within the 40 detected PGCCs and identify them as cores. Out of a total of 119 cores, 15 cores are discovered in the λ Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the λ Orionis cloud show much lower mean values of size R = 0.08 pc, column density N(H2) = (9.5 ± 1.2) × 1022 cm−2, number density n(H2) = (2.9 ± 0.4) × 105 cm−3, and mass M core = 1.0 ± 0.3 M ⊙ compared to the cores in the Orion A [R = 0.11 pc, N(H2) = (2.3 ± 0.3) × 1023 cm−2, n(H2) = (3.8 ± 0.5) × 105 cm−3, and M core = 2.4 ± 0.3 M ⊙] and Orion B [R = 0.16 pc, N(H2) = (3.8 ± 0.4) × 1023 cm−2, n(H2) = (15.6 ± 1.8) × 105 cm−3, and M core = 2.7 ± 0.3 M ⊙] clouds. These core properties in the λ Orionis cloud can be attributed to the photodissociation and external heating by the nearby H II region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.