arXiv subjects

Shigehisa Takakuwa

Publications and source records attributed to Shigehisa Takakuwa.

At least 91 records · Page 5Linked to original sources

arXiv2014

IRAS16547-4247: A New Candidate of a Protocluster Unveiled with ALMA

We present the results of continuum and 12CO(3-2) and CH3OH(7-6) line observations of IRAS16547-4247 made with the Atacama Large Millimeter/submillimeter Array (ALMA) at an angular resolution of ~0.5". The 12CO(3-2) emission shows two high-velocity outflows whose driving sources are located within the dust continuum peak. The alignment of these outflows do not coincide with that of the wide-angle, large scale, bipolar outflow detected with APEX in previous studies. The CH3OH(7-6) line emission traces an hourglass structure associated with the cavity walls created by the outflow lobes. Taking into account our results together with the position of the H2O and class I CH3OH maser clusters, we discuss two possible scenarios that can explain the hourglass structure observed in IRAS16547-4247: (1) precession of a biconical jet, (2) multiple, or at least two, driving sources powering intersecting outflows. Combining the available evidence, namely, the presence of two cross-aligned bipolar outflows and two different H2O maser groups, we suggest that IRAS16547-4247 represents an early formation phase of a protocluster.

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arXiv2014

Transition from the Infalling Envelope to the Keplerian Disk around L1551 IRS 5

We present combined SubMillimeter Array (SMA) + Atacama Submillimeter Telescope Experiment (ASTE) images of the Class I protobinary L1551 IRS 5 in the CS ($J$ = 7--6) line, the submillimeter images of L1551 IRS 5 with the most complete spatial sampling ever achieved ($0''.9$ -- $36''$). The SMA image of L1551 IRS 5 in the 343 GHz dust-continuum emission is also presented, which shows an elongated feature along the northwest to southeast direction ($\sim$160 AU $\times$ 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity ($\gtrsim$1.5 km s$^{-1}$) CS emission traces the structure of the dust component and shows a velocity gradient along the major axis, which is reproduced by a geometrically-thin Keplerian-disk model with a central stellar mass of $\sim$0.5 $M_{\odot}$. The low-velocity ($\lesssim$1.3 km s$^{-1}$) CS emission shows an extended ($\sim$1000 AU) feature that exhibits slight south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of $\sim$64 AU. The infalling velocity of the envelope is $\sim$three times lower than the free-fall velocity toward the central stellar mass of 0.5 $M_{\odot}$. These results demonstrate transition from the infalling envelope to the Keplerian disk, consistent with the latest theoretical studies of disk formation. We suggest that sizable ($r\sim$50--200 AU) Keplerian disks are already formed when the protostars are still deeply embedded in the envelopes.

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arXiv2014

Formation of a Keplerian disk in the infalling envelope around L1527 IRS: transformation from infalling motions to Kepler motions

We report Atacama Large Millimeter/submillimeter Array (ALMA) cycle 0 observations of C$^{18}$O ($J=2-1$), SO ($J_N= 6_5-5_4$) and 1.3mm dust continuum toward L1527 IRS, a class 0 solar-type protostar surrounded by an infalling and rotating envelope. C$^{18}$O emission shows strong redshifted absorption against the bright continuum emission associated with L1527 IRS, strongly suggesting infall motions in the C$^{18}$O envelope. The C$^{18}$O envelope also rotates with a velocity mostly proportional to $r^{-1}$, where $r$ is the radius, while the rotation profile at the innermost radius (54 AU) may be shallower than $r^{-1}$, suggestive of formation of a Keplerian disk around the central protostar of 0.3 Mo in dynamical mass. SO emission arising from the inner part of the C$^{18}$O envelope also shows rotation in the same direction as the C$^{18}$O envelope. The rotation is, however, rigid-body like which is very different from the differential rotation shown by C$^{18}$O. In order to explain the line profiles and the position-velocity (PV) diagrams of C$^{18}$O and SO observed, simple models composed of an infalling envelope surrounding a Keplerian disk of 54 AU in radius orbiting a star of 0.3 Mo are examined. It is found that in order to reproduce characteristic features of the observed line profiles and PV diagrams, the infall velocity in the model has to be smaller than the free-fall velocity yielded by a star of 0.3 Mo. Possible reasons for the reduced infall velocities are discussed.

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arXiv2014

Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE

We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped brightenings in the circumbinary disk, and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly-observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

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arXiv2014

ALMA Observations of Infalling Flows toward the Keplerian Disk around the Class I Protostar L1489 IRS

We have conducted ALMA observations in the 1.3 mm continuum and 12CO (2-1), C18O (2-1) and SO (5_6-4_5) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the 12CO and C18O emission, and its outer radius (~700 AU) and mass (~0.005 Msun) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 Msun with the inclination angle of 66 deg. In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C18O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ~5E-7 Msun/yr. The specific angular momentum of the infalling flows (~2.5E-3 km/s*pc) is comparable to that at the outer radius of the Keplerian disk (~4.8E-3 km/s*pc). The SO emission is elongated along the disk major axis and exhibits a linear velocity gradient along the axis, which is interpreted as that the SO emission primarily traces a ring region in the flared Keplerian disk at radii of ~250-390 AU. The local enhancement of the SO abundance in the ring region can be due to the accretion shocks at the centrifugal radius where the infalling flows fall onto the disk. Our ALMA observations unveiled both the Keplerian disk and the infalling gas onto the disk, and the disk can further grow by accreting material and angular momenta from the infalling gas.

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arXiv2014

The Disappearing Envelope around the Transitional Class I Object L43

We present SMA interferometric observations of the 12CO J=2-1, 13CO (J=2-1), and C18O (J=2-1) lines and 225 GHz continuum emission and SMT single-dish observations of C18O (J=2-1) toward L43, a protostellar object in transition from Class I to II. The 225 GHz continuum emission shows a weak (~23.6 mJy), compact (<1000 AU) component associated with the central protostar. Our simulated observations show that it can be explained by dust thermal emission arising from an envelope which has a hole or a constant intensity region within a few hundred AU of the protostar. This suggests the disappearance or a lower concentration distribution of the envelope on a small scale. The 12CO and 13CO emission exhibit molecular outflows to the south and north. The C18O emission shows two molecular blobs, which correspond to the reflection nebulosity seen in near-infrared images, while there is no C18O emission associated with the protostar. The near-infrared features are likely due to the scattering at the positions of the blobs. The visible scattering features should result from the optical thinness of the envelope material, which is consistent with the less-concentrated distribution in the continuum emission. From single-dish observations, we found that the mass of the envelope (~1.5 Msun) + protostar (~0.5 Msun) is comparable with the virial mass of M_vir=1.0 Msun within 40 arcsec. This suggests that the envelope is likely gravitationally bound. We suggest that the protostellar envelope of L43 has been disappearing by consumption through accretion, at least in the close vicinity of the protostar.

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arXiv2013

Evidence for Infalling Gas of Low Angular Momentum towards the L1551 NE Keplerian Circumbinary Disk

We report follow-up observations of the Class I binary protostellar system L1551 NE in the C18O (3--2) line with the SMA in its compact and subcompact configurations. Our previous observations at a higher angular resolution in the extended configuration revealed a circumbinary disk exhibiting Keplerian motion. The combined data having more extensive spatial coverage (~140 - 2000 AU) verify the presence of a Keplerian circumbinary disk, and reveals for the first time a distinct low-velocity (~< +-0.5 km s-1 from the systemic velocity) component that displays a velocity gradient along the minor axis of the circumbinary disk. Our simple model that reproduces the main features seen in the Position-Velocity diagrams comprises a circumbinary disk exhibiting Keplerian motion out to a radius of ~300 AU, beyond which the gas exhibits pure infall at a constant velocity of ~0.6 km s-1. The latter is significantly smaller than the expected free-fall velocity of ~2.2 km s-1 onto the L1551 NE protostellar mass of ~0.8 Msun at ~300 AU, suggesting that the infalling gas is decelerated as it moves into regions of high gas pressure in the circumbinary disk. The discontinuity in angular momenta between the outer infalling gas and inner Keplerian circumbinary disk implies an abrupt transition in the effectiveness at which magnetic braking is able to transfer angular momentum outwards, a result perhaps of the different plasma beta and ionization fractions between the outer and inner regions of the circumbinary disk.

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arXiv2013

Unveiling the Evolutionary Sequence from Infalling Envelopes to Keplerian Disks around Low-Mass Protostars

We performed SMA observations in the C18O (2-1) emission line toward six Class 0 and I protostars, to study rotational motions of their surrounding envelopes and circumstellar material on 100 to 1000 AU scales. C18O (2-1) emission with intensity peaks located at the protostellar positions is detected toward all the six sources. The rotational velocities of the protostellar envelopes as a function of radius were measured from the Position-Velocity diagrams perpendicular to the outflow directions passing through the protostellar positions. Two Class 0 sources, B335 and NGC 1333 IRAS 4B, show no detectable rotational motion, while L1527 IRS (Class 0/I) and L1448-mm (Class 0) exhibit rotational motions with radial profiles of Vrot ~ r^{-1.0+/-0.2} and ~ r^{-1.0+/-0.1}, respectively. The other Class I sources, TMC-1A and L1489 IRS, exhibit the fastest rotational motions among the sample, and their rotational motions have flatter radial profiles of Vrot ~ r^{-0.6+/-0.1} and ~ r^{-0.5+/-0.1}, respectively. The rotational motions with the radial dependence of ~ r^{-1} can be interpreted as rotation with a conserved angular momentum in a dynamically infalling envelope, while those with the radial dependence of ~ r^{-0.5} can be interpreted as Keplerian rotation. These observational results demonstrate categorization of rotational motions from infalling envelopes to Keplerian-disk formation. Models of the inside-out collapse where the angular momentum is conserved are discussed and compared with our observational results.

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arXiv2012

Substellar-Mass Condensations in Prestellar Cores

We present combined Submillimeter-Array (SMA) + single-dish images of the (sub)millimeter dust continuum emission toward two prestellar cores SM1 and B2-N5 in the nearest star cluster forming region, $ρ$ Ophiuchus. Our combined images indicate that SM1 and B2-N5 consist of three and four condensations, respectively, with masses of $10^{-2}-10^{-1}M_\odot$ and sizes of a few hundred AU. The individual condensations have mean densities of $10^8-10^9$ cm$^{-3}$ and the masses are comparable to or larger than the critical Bonner-Ebert mass, indicating that the self-gravity plays an important role in the dynamical evolution of the condensations. The coalescence timescale of these condensations is estimated to be about $10^4$ yr, which is comparable to the local gravitational collapse timescale, suggesting that merging of the condensations, instead of accretion, plays an essential role in the star formation process. These results challenge the standard theory of star formation, where a single, rather featureless prestellar core collapses to form at most a couple of condensations, each of which potentially evolves into a protostar that is surrounded by a rotating disk where planets are created.

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arXiv2012

A Keplerian Circumbinary Disk around the Protobinary System L1551 NE

We present SubMillimeter-Array observations of a Keplerian disk around the Class I protobinary system L1551 NE in 335 GHz continuum emission and submillimeter line emission in 13CO (J=3-2) and C18O (J=3-2) at a resolution of ~120 x 80 AU. The 335-GHz dust-continuum image shows a strong central peak closely coincident with the binary protostars and likely corresponding to circumstellar disks, surrounded by a ~600 x 300 AU feature elongated approximately perpendicular to the [Fe II] jet from the southern protostellar component suggestive of a circumbinary disk. The 13CO and C18O images confirm that the circumbinary continuum feature is indeed a rotating disk; furthermore, the C18O channel maps can be well modeled by a geometrically-thin disk exhibiting Keplerian rotation. We estimate a mass for the circumbinary disk of ~0.03-0.12 Msun, compared with an enclosed mass of ~0.8 Msun that is dominated by the protobinary system. Compared with several other Class I protostars known to exhibit Keplerian disks, L1551 NE has the lowest bolometric temperature (~91 K), highest envelope mass (~0.39 Msun), and the lowest ratio in stellar mass to envelope + disk + stellar mass (~0.65). L1551 NE may therefore be the youngest protostellar object so far found to exhibit a Keplerian disk. Our observations present firm evidence that Keplerian disks around binary protostellar systems, ``Keplerian circumbinary disks', can exist. We speculate that tidal effects from binary companions could transport angular momenta toward the inner edge of the circumbinary disk and create the Keplerian circumbinary disk.

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arXiv2011

Kinematics and Physical Conditions of the Innermost Envelope in B335

We made C18O (2-1) and CS (7-6) images of the protostellar envelope around B335 with a high spatial dynamic range from ~10000 to ~400 AU, by combining the Submillimeter Array and single-dish data. The C18O emission shows an extended (~10000 AU) structure as well as a compact (~1500 AU) component concentrated at the protostellar position. The CS emission shows a compact (~900 AU) component surrounding the protostar, plus a halo-like (~3000 AU) structure elongated along the east-west direction. At higher velocities (|dV| >~0.3 km s^-1), the CS emission is stronger and more extended than the C18O emission. Physical conditions of the envelope were examined through an LVG model. At |dV| >~0.3 km s^-1, the gas temperature is higher (>40 K) than that at |dV| <~0.3 km s^-1, whereas the gas density is lower (<10^6 cm^-3). We consider that the higher-temperature and lower-density gas at |dV| >~0.3 km s^-1 is related to the associated outflow, while the lower-temperature and higher-density gas at |dV| <~0.3 km s^-1 is the envelope component. From the inspection of the positional offsets in the velocity channel maps, the radial profile of the specific angular momentum of the envelope rotation in B335 was revealed at radii from ~10^4 down to ~10^2 AU. The specific angular momentum decreases down to the radius of ~370 AU, and then appears to be conserved within that radius. A possible scenario of the evolution of envelope rotation is discussed.

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arXiv2011

Arcsecond resolution images of the chemical structure of the low-mass protostar IRAS 16293-2422

It remains a key challenge to establish the molecular content of different components of low-mass protostars, like their envelopes and disks, and how this depends on the evolutionary stage and/or environment of the young stars. Observations at submillimeter wavelengths provide a direct possibility to study the chemical composition of low-mass protostars through transitions probing temperatures up to a few hundred K in the gas surrounding these sources. This paper presents a large molecular line survey of the deeply embedded protostellar binary IRAS 16293-2422 from the Submillimeter Array (SMA) - including images of individual lines down to approximately 1.5-3" (190-380 AU) resolution. More than 500 individual transitions are identified related to 54 molecular species (including isotopologues) probing temperatures up to about 550 K. Strong chemical differences are found between the two components in the protostellar system with a separation between, in particular, the sulfur- and nitrogen-bearing species and oxygen-bearing complex organics. The action of protostellar outflow on the ambient envelope material is seen in images of CO and SiO and appear to influence a number of other species, including (deuterated) water, HDO. The effects of cold gas-phase chemistry is directly imaged through maps of CO, N2D+ and DCO+, showing enhancements of first DCO+ and subsequently N2D+ in the outer envelope where CO freezes-out on dust grains.

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arXiv2011

Skewed Distributions and Opposite Velocity Gradients of Submillimeter Molecular Lines in Low-Mass Protostellar Envelopes

We have made mapping observations of L1551 IRS 5, L1551NE, L723, and L43 and single-point observations of IRAS 16293-2422 in the submillimeter CS (J = 7-6) and HCN (J = 4-3) lines with ASTE. Including our previous ASTE observations of L483 and B335, we found a clear linear correlation between the source bolometric luminosities and the total integrated intensities of the submillimeter lines (I_CS ~L_bol^0.92). The combined ASTE + SMA CS (7-6) image of L1551 IRS 5 exhibits an extended (~2000 AU) component tracing the associated reflection nebula at the west and southwest, as well as a compact (< 500 AU) component centered on the protostellar position. The emission peaks of the CS and HCN emissions in L1551 NE are not located at the protostellar position but offset (~1400 AU) toward the associated reflection nebula at the west. With the statistical analyses, we confirmed the opposite velocity gradients of the CS (7-6) emission to those of the millimeter lines along the outflow direction, which we reported in our early paper. The magnitudes of the submillimeter velocity gradients are estimated to be (9.7\pm1.7) \times 10-3 km s-1 arcsec-1 in L1551 IRS 5 and (7.6\pm2.4) \times 10-3 km s-1 arcsec-1 in L483. We suggest that the "skewed" submillimeter molecular emissions toward the associated reflection nebulae at a few thousands AU scale trace the warm (> 40 K) walls of the envelope cavities, excavated by the associated outflows and irradiated by the central protostars directly. The opposite velocity gradients along the outflow direction likely reflect the dispersing gas motion at the wall of the cavity in the envelopes perpendicular to the outflow.

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arXiv2010

Carbon-Chain and Organic Molecules around Very Low-Luminosity Protostellar Objects of L1521F-IRS and IRAM 04191+1522

We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Towards L1521F-IRS, carbon-chain lines of CH3CCH (50-40), C4H (17/2-15/2), and C3H2 (212-101) are 1.5 - 3.5 times stronger than those towards IRAM 04191+1522, and the abundances of the carbon-chain molecules towards L1521F-IRS are 2 to 5 times higher than those towards IRAM 04191+1522. Mapping observations of these carbon-chain molecular lines show that in L1521F the peak positions of these carbon-chain molecular lines are different from each other and there is no emission peak towards the VeLLO position, while in IRAM 04191+1522 these carbon-chain lines are as weak as the detection limits except for the C3H2 line. The observed chemical differentiation between L1521F and IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS is younger than that of IRAM 04191+1522, consistent with the extent of the associated outflows seen in the 13CO (1-0) line. The non-detection of the organic molecular lines of CH3OH (6-2-7-1 E) and CH3CN (60-50) implies that the warm (~ 100 K) molecular-desorbing region heated by the central protostar is smaller than ~ 100 AU towards L1521F-IRS and IRAM 04191+1522, suggesting the young age of these VeLLOs. We propose that the chemical status of surrounding dense gas can be used to trace the evolutionary stages of VeLLOs.

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arXiv2010

New Panoramic View of $^{12}$CO and 1.1 mm Continuum Emission in the Orion A Molecular Cloud. I. Survey Overview and Possible External Triggers of Star Formation

We present new, wide and deep images in the 1.1 mm continuum and the $^{12}$CO ($J$=1-0) emission toward the northern part of the Orion A Giant Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in Chile, and the $^{12}$CO ($J$=1-0) data were with the 25 beam receiver (BEARS) on the NRO 45 m telescope in the On-The-Fly (OTF) mode. The present AzTEC observations are the widest $(\timeform{1.D7}$ $\times$ $\timeform{2.D3}$, corresponding to 12 pc $\times$ 17 pc) and the highest-sensitivity ($\sim$9 mJy beam$^{-1}$) 1.1 mm dust-continuum imaging of the Orion-A GMC with an effective spatial resolution of $\sim$ 40$\arcsec$. The $^{12}$CO ($J$=1-0) image was taken over the northern $\timeform{1D.2} \times\timeform{1D.2}$ (corresponding 9 pc $\times$ 9 pc) area with a sensitivity of 0.93 K in $T_{\rm MB}$, a velocity resolution of 1.0 km s$^{-1}$, and an effective spatial resolution of 21$\arcsec$. With these data, together with the MSX 8 $μ$m, Spitzer 24 $μ$m and the 2MASS data, we have investigated the detailed structure and kinematics of molecular gas associated with the Orion-A GMC and have found evidence for interactions between molecular clouds and the external forces that may trigger star formation. Two types of possible triggers were revealed; 1) Collision of the diffuse gas on the cloud surface, particularly at the eastern side of the OMC-2/3 region, and 2) Irradiation of UV on the pre-existing filaments and dense molecular cloud cores. Our wide-field and high-sensitivity imaging have provided the first comprehensive view of the potential sites of triggered star formation in the Orion-A GMC.

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arXiv2010

Outflow - Core Interaction in Barnard 1

In order to study how outflows from protostars influence the physical and chemical conditions of the parent molecular cloud, we have observed Barnard 1 (B1) main core, which harbors four Class 0 and three Class I sources, in the CO (J=1-0), CH3OH (J_K=2_K-1_K), and the SiO (J=1-0) lines using the Nobeyama 45 m telescope. We have identified three CO outflows in this region; one is an elongated (~ 0.3 pc) bipolar outflow from a Class 0 protostar B1-c in the submillimeter clump SMM 2, another is a rather compact (~ 0.1 pc) outflow from a Class I protostar B1 IRS in the clump SMM 6, and the other is an extended outflow from a Class I protostar in SMM 11. In the western lobe of the SMM 2 outflow, both the SiO and CH3OH lines show broad redshifted wings with the terminal velocities of 25 km/s and 13 km/s, respectively. It is likely that the shocks caused by the interaction between the outflow and ambient gas enhance the abundance of SiO and CH3OH in the gas phase. The total energy input rate by the outflows (1.1x10^{-3} Lsun) is smaller than the energy loss rate (8.5x10^{-3} Lsun$) through the turbulence decay in B1 main core, which suggests that the outflows can not sustain the turbulence in this region. Since the outflows are energetic enough to compensate the dissipating turbulence energy in the neighboring, more evolved star forming region NGC 1333, we suggest that the turbulence energy balance depends on the evolutionary state of the star formation in molecular clouds.

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arXiv2010

High-Velocity Jets and Slowly Rotating Envelope in B335

We have performed detailed imaging and analyses of SMA observations in 230 GHz continuum, 12CO (2-1), 13CO (2-1), and C18O (2-1) emission toward B335, a Bok globule with an embedded Class 0 source (Lbol ~ 1.5 Lsun). We report the first discover of high-velocity 12CO jets with a size of ~ 900 AU x 1500 AU along the E-W direction in B335. The estimated mass-loss rate (~ 2.3 x 10^-7 Msun yr^-1) and the momentum flux (~ 3.7 x 10^-5 Msun yr^-1 km s^-1) of the 12CO jets in B335 are one order of magnitude lower than those of other 12CO jets in more luminous sources such as HH 211 (Lbol ~ 3.6 Lsun) and HH 212 (Lbol ~ 14 Lsun). The weaker jet activity in B335 could be due to the lower active accretion onto the central protostar. The C18O emission shows a compact (~ 1500 AU) condensation associated with the central protostar, and it likely traces the protostellar envelope around B335. The envelope exhibits a velocity gradient from the east (blueshifted) to west (redshifted) that can be interpreted as an infalling motion. The estimated central stellar mass, the mass infalling rate, and the accretion luminosity are 0.04 Msun, 6.9 x 10^-6 Msun yr^-1, and 2.1 Lsun, respectively. On the other hand, there is no clear velocity gradient perpendicular to the outflow axis in the C18O envelope, suggesting little envelope rotation on a hundred-AU scale. The upper limits of the rotational velocity and specific angular momentum were estimated to be 0.04 km s^-1 and 7.0 x 10^-5 km s^-1 pc at a radius of 370 AU, respectively. The specific angular momentum and the inferred Keplerian radius (~ 6 AU) in B335 are 1 - 2 orders of magnitude smaller than those in other more-evolved sources. Possible scenarios to explain the lower specific angular momentum in B335 are discussed.

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arXiv2009

Millimeter- and Submillimeter-Wave Observations of the OMC-2/3 region. IV Interaction between the Outflow and the Dense Gas in the Cluster Forming Region of OMC-2 FIR 6

We have conducted millimeter interferometric observations of the Orion Molecular Cloud-2 (OMC-2) FIR 6 region at an angular resolution of $\sim$ 4$\arcsec$ - 7$\arcsec$ with the Nobeyama Millimeter Array (NMA). In the 3.3 mm continuum emission we detected dusty core counterparts of the previously identified FIR sources (FIR 6a, 6b, 6c, and 6d), and moreover, resolved FIR 6a into three dusty cores. The size and mass of these cores are estimated to be 1100-5900 AU and 0.19-5.5 M$_{\odot}$, respectively. We found that in the $^{12}$CO ($J$=1--0) emission FIR 6b, 6c, and 6d eject the molecular outflow and that the FIR 6c outflow also exhibits at least two collimated jet-like components in the SiO ($J$=2--1) emission. At the tip of one of the SiO components there appears abrupt increase of the SiO line width ($\sim$ 15 km s$^{-1}$), where the three resolved cores in FIR 6a seem to delineate the tip. These results imply the presence of the interaction and the bowshock front between the FIR 6c molecular outflow and FIR 6a.

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