Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ad003a

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/acfd24

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/acf7c1

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

We present high-resolution high-sensitivity observations of the Class 0 protostar RCrA IRS5N as part of the Atacama Large Milimeter/submilimeter Array large program Early Planet Formation in Embedded Disks. The 1.3 mm continuum emission reveals a flattened continuum structure around IRS5N, consistent with a protostellar disk in the early phases of evolution. The continuum emission appears smooth and shows no substructures. However, a brightness asymmetry is observed along the minor axis of the disk, suggesting that the disk is optically and geometrically thick. We estimate the disk mass to be between 0.007 and 0.02 M ⊙. Furthermore, molecular emission has been detected from various species, including C18O (2-1), 12CO (2-1), 13CO (2-1), and H2CO (30,3 - 20,2, 32,1 - 22,0, and 32,2 - 22,1). By conducting a position-velocity analysis of the C18O (2-1) emission, we find that the disk of IRS5N exhibits characteristics consistent with Keplerian rotation around a central protostar with a mass of approximately 0.3 M ⊙. Additionally, we observe dust continuum emission from the nearby binary source IRS5a/b. The emission in 12CO toward IRS5a/b seems to emanate from IRS5b and flow into IRS5a, suggesting material transport between their mutual orbits. The lack of a detected outflow and large-scale negatives in 12CO observed toward IRS5N suggests that much of the flux from IRS5N is being resolved out. Using a 1D radiative transfer model, we infer the mass of the envelope surrounding IRS5N to be 1/41.2 M ⊙. Due to this substantial surrounding envelope, the central IRS5N protostar is expected to be significantly more massive in the future.

DOI： 10.3847/1538-4357/ace35c

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

Precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown dwarfs (BDs; M * < 0.08 M ☉). The most accurate estimation of protostellar mass uses the Keplerian rotation in the circumstellar disk around the protostar. To apply the Keplerian rotation method to a protostar at the low-mass end, we have observed the Class 0 protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.″07 (10 au), and in the 12CO, C18O, 13CO (J = 2-1), and SO (J N = 65−54) molecular lines, as part of the ALMA Large Program Early Planet Formation in Embedded Disks project. The continuum emission traces a nonaxisymmetric, disk-like structure perpendicular to the associated 12CO outflow. The position-velocity (PV) diagrams in the C18O and 13CO lines can be interpreted as infalling and rotating motions. In contrast, the PV diagram along the major axis of the disk-like structure in the 12CO line allows us to identify Keplerian rotation. The central stellar mass and the disk radius are estimated to be ∼0.12-0.17 M ☉ and ∼13-19 au, respectively. The SO line suggests the existence of an accretion shock at a ring (r ∼ 28 au) surrounding the disk and a streamer from the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a central stellar mass close to the BD mass regime, and our results provide a typical picture of such very-low-mass protostars.

DOI： 10.3847/1538-4357/ace624

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

We have observed the Class 0/I protostellar system Ced110 IRS4 at an angular resolution of 0.″05 ( 1/410 au) as part of the Atacama Large Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks. The 1.3 mm dust continuum emission reveals that Ced110 IRS4 is a binary system with a projected separation of 1/4250 au. The continuum emissions associated with the main source and its companion, named Ced110 IRS4A and IRS4B, respectively, exhibit disk-like shapes and likely arise from dust disks around the protostars. The continuum emission of Ced110 IRS4A has a radius of 1/4110 au ( 1/40.″6) and shows bumps along its major axis with an asymmetry. The bumps can be interpreted as a shallow, ring-like structure at a radius of 1/440 au ( 1/40.″2) in the continuum emission, as demonstrated from two-dimensional intensity distribution models. A rotation curve analysis on the C18O and 13CO J = 2-1 lines reveals the presence of a Keplerian disk within a radius of 120 au around Ced110 IRS4A, which supports the interpretation that the dust continuum emission arises from a disk. The ring-like structure in the dust continuum emission might indicate a possible annular substructure in the surface density of the embedded disk, although the possibility that it is an apparent structure due to the optically thick continuum emission cannot be ruled out.

DOI： 10.3847/1538-4357/ace52d

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC₅N (J = 35–34) line has been detected from three MYSOs, where nitrogen (N)-bearing COMs (CH₂CHCN and CH₃CH₂CN) have been detected. The HC₅N spatial distributions show compact features and match with a methanol (CH₃OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC₅N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC₅N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs.

DOI： 10.3847/1538-4365/acd110

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4365/acd110/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

Studying the physical and chemical conditions of young embedded disks is crucial to constrain the initial conditions for planet formation. Here we present Atacama Large Millimeter/submillimeter Array observations of dust continuum at ∼0.″06 (8 au) resolution and molecular line emission at ∼0.″17 (24 au) resolution toward the Class 0 protostar L1527 IRS from the Large Program eDisk (Early Planet Formation in Embedded Disks). The continuum emission is smooth without substructures but asymmetric along both the major and minor axes of the disk as previously observed. The detected lines of 12CO, 13CO, C18O, H2CO, c-C3H2, SO, SiO, and DCN trace different components of the protostellar system, with a disk wind potentially visible in 12CO. The 13CO brightness temperature and the H2CO line ratio confirm that the disk is too warm for CO freezeout, with the snowline located at ∼350 au in the envelope. Both molecules show potential evidence of a temperature increase around the disk-envelope interface. SO seems to originate predominantly in UV-irradiated regions such as the disk surface and the outflow cavity walls rather than at the disk-envelope interface as previously suggested. Finally, the continuum asymmetry along the minor axis is consistent with the inclination derived from the large-scale (100″ or 14,000 au) outflow, but opposite to that based on the molecular jet and envelope emission, suggesting a misalignment in the system. Overall, these results highlight the importance of observing multiple molecular species in multiple transitions to characterize the physical and chemical environment of young disks.

DOI： 10.3847/1538-4357/accf87

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

While dust disks around optically visible, Class II protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. As part of the Atacama Large Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks, we analyze the edge-on, embedded, Class I protostar IRAS 04302+2247, also nicknamed the “Butterfly Star.” With a resolution of 0.″05 (8 au), the 1.3 mm continuum shows an asymmetry along the minor axis that is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. There is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. With 0.″1 (16 au) resolution, we resolve the 2D snow surfaces, i.e., the boundary region between freeze-out and sublimation, for 12CO J = 2-1, 13CO J = 2-1, C18O J = 2-1, H 2CO J = 30,3-20,2, and SO J = 65-54, and constrain the CO midplane snow line to ∼130 au. We find Keplerian rotation around a protostar of 1.6 ± 0.4 M ⊙ using C18O. Through forward ray-tracing using RADMC-3D, we find that the dust scale height is ∼6 au at a radius of 100 au from the central star and is comparable to the gas pressure scale height. The results suggest that the dust of this Class I source has yet to vertically settle significantly.

DOI： 10.3847/1538-4357/acd5c9

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present an overview of the Large Program, “Early Planet Formation in Embedded Disks (eDisk),” conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The ubiquitous detections of substructures, particularly rings and gaps, in protoplanetary disks around T Tauri stars raise the possibility that at least some planet formation may have already started during the embedded stages of star formation. In order to address exactly how and when planet formation is initiated, the program focuses on searching for substructures in disks around 12 Class 0 and 7 Class I protostars in nearby (&lt;200 pc) star-forming regions through 1.3 mm continuum observations at a resolution of ∼7 au (0.″04). The initial results show that the continuum emission, mostly arising from dust disks around the sample protostars, has relatively few distinctive substructures, such as rings and spirals, in marked contrast to Class II disks. The dramatic difference may suggest that substructures quickly develop in disks when the systems evolve from protostars to Class II sources, or alternatively that high optical depth of the continuum emission could obscure internal structures. Kinematic information obtained through CO isotopologue lines and other lines reveals the presence of Keplerian disks around protostars, providing us with crucial physical parameters, in particular, the dynamical mass of the central protostars. We describe the background of the eDisk program, the sample selection and their ALMA observations, and the data reduction, and we also highlight representative first-look results.

DOI： 10.3847/1538-4357/acd384

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acd384/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

Constraining the physical and chemical structure of young embedded disks is crucial for understanding the earliest stages of planet formation. As part of the Early Planet Formation in Embedded Disks Atacama Large Millimeter/submillimeter Array Large Program, we present high spatial resolution (∼0.″1 or ∼15 au) observations of the 1.3 mm continuum and ¹³CO J = 2–1, C¹⁸O J = 2–1, and SO J_N = 6₅–5₄ molecular lines toward the disk around the Class I protostar L1489 IRS. The continuum emission shows a ring-like structure at 56 au from the central protostar and tenuous, optically thin emission extending beyond ∼300 au. The ¹³CO emission traces the warm disk surface, while the C¹⁸O emission originates from near the disk midplane. The coincidence of the radial emission peak of C¹⁸O with the dust ring may indicate a gap-ring structure in the gaseous disk as well. The SO emission shows a highly complex distribution, including a compact, prominent component at ≲30 au, which is likely to originate from thermally sublimated SO molecules. The compact SO emission also shows a velocity gradient along a direction tilted slightly (∼15°) with respect to the major axis of the dust disk, which we interpret as an inner warped disk in addition to the warp around ∼200 au suggested by previous work. These warped structures may be formed by a planet or companion with an inclined orbit, or by a gradual change in the angular momentum axis during gas infall.

DOI： 10.3847/1538-4357/accd71

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/accd71/pdf

Language：English   Publishing type：Research paper (scientific journal)  

We present high angular resolution measurements of the thermal Sunyaev–Zel’dovich effect (SZE) toward two galaxy clusters, RCS J2319+0038 at z = 0.9 and HSC J0947−0119 at z = 1.1, by the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. They are supplemented with available Chandra X-ray data, optical data taken by Hyper Suprime-Cam on Subaru, and millimeter-wave SZE data from the Atacama Cosmology Telescope. Taking into account departures from spherical symmetry, we have reconstructed non-parametrically the inner pressure profile of two clusters as well as electron temperature and density profiles for RCS J2319+0038. This is one of the first such measurements for an individual cluster at z ≳ 0.9. We find that the inner pressure profile of both clusters is much shallower than that of local cool-core clusters. Our results consistently suggest that RCS J2319+0038 hosts a weak cool core, where radiative cooling is less significant than in local cool cores. On the other hand, HSC J0947−0119 exhibits an even shallower pressure profile than RCS J2319+0038 and is more likely to be a non-cool-core cluster. The SZE centroid position is offset by more than 140 h−170 kpc from the peaks of galaxy distribution in HSC J0947−0119, suggesting a stronger influence of mergers in this cluster. We conclude that these distant clusters are at a very early stage of developing the cool cores typically found in clusters at lower redshifts.

DOI： 10.1093/pasj/psac110

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

To study the transportation of magnetic flux from large to small scales in protostellar sources, we analyzed the Nobeyama 45 m N₂H⁺ (1–0), JCMT 850 μm polarization, and Atacama Large Millimeter/submillimeter Array (ALMA) C¹⁸O (2–1) and 1.3 and 0.8 mm (polarized) continuum data of the Class 0 protostar HH 211. The magnetic field strength in the dense core on a 0.1 pc scale was estimated with the single-dish line and polarization data using the Davis–Chandrasekhar–Fermi method, and that in the protostellar envelope on a 600 au scale was estimated from the force balance between the gravity and magnetic field tension by analyzing the gas kinematics and magnetic field structures with the ALMA data. Our analysis suggests that from 0.1 pc–600 au scales, the magnetic field strength increases from 40–107 μG to 0.3–1.2 mG with a scaling relation between the magnetic field strength and density of B ∝ ρ ^0.36±0.08, and the mass-to-flux ratio increases from 1.2–3.7 to 9.1–32.3. The increase in the mass-to-flux ratio could suggest that the magnetic field is partially decoupled from the neutral matter between 0.1 pc and 600 au scales, and hint at efficient ambipolar diffusion in the infalling protostellar envelope in HH 211, which is the dominant nonideal magnetohydrodynamic effect considering the density on these scales. Thus, our results could support the scenario of efficient ambipolar diffusion enabling the formation of the 20 au Keplerian disk in HH 211.

DOI： 10.3847/1538-4357/aca47f

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/aca47f/pdf

Language：Japanese   Publisher：Bone Reports  

Pseudohypoparathyroidism 1A (PHP1A) and pseudopseudohypoparathyroidism (PPHP) are caused by loss-of-function variants of GNAS, which encodes Gsα. We present two unrelated Japanese families with PHP1A and PPHP harboring unreported pathogenic variants of GNAS (c.1141delG, p.Asp381Thrfs*23 and c.1117delC, p.Arg373Alafs*31). These variants introduce abnormal amino acids in the β6 strand/α5 helix of Gsα, which interact with G protein coupling receptor (GPCR). We conclude that these variants alter the association of Gsα with GPCR and cause PHP1A or PPHP.

DOI： 10.1016/j.bonr.2022.101637

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astrophysical Journal  

We present high-resolution Karl G. Jansky Very Large Array (VLA) observations of the protostar L1527 IRS at 7 mm, 1.3 cm, and 2 cm wavelengths. We detect the edge-on dust disk at all three wavelengths and find that it is asymmetric, with the southern side of the disk brighter than the northern side. We confirm this asymmetry through analytic modeling and also find that the disk is flared at 7 mm. We test the data against models including gap features in the intensity profile, and though we cannot rule such models out, they do not provide a statistically significant improvement in the quality of fit to the data. From these fits, we can, however, place constraints on allowed properties of any gaps that could be present in the true, underlying intensity profile. The physical nature of the asymmetry is difficult to associate with physical features owing to the edge-on nature of the disk, but it could be related to spiral arms or asymmetries seen in other imaging of more face-on disks.

DOI： 10.3847/1538-4357/ac7a3b

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of the hypercompact H ii region G24.78+0.08 A1 (G24 HC H ii) and report the detection of vibrationally excited lines of HC₃N (v₇ = 2, J = 24 − 23). The spatial distribution and kinematics of a vibrationally excited line of HC₃N (v₇ = 2, J = 24 − 23, l = 2e) are found to be similar to the CH₃CN vibrationally excited line (v₈ = 1), which indicates that the HC₃N emission is tracing the disk around the G24 HC H ii region previously identified by the CH₃CN lines. We derive the ¹³CH₃CN/HC¹³CCN abundance ratios around G24 and compare them to the CH₃CN/HC₃N abundance ratios in disks around Herbig Ae and T Tauri stars. The ¹³CH₃CN/HC¹³CCN ratios around G24 (∼3.0–3.5) are higher than the CH₃CN/HC₃N ratios in the other disks (∼0.03–0.11) by more than 1 order of magnitude. The higher CH₃CN/HC₃N ratios around G24 suggest that the thermal desorption of CH₃CN in the hot dense gas and efficient destruction of HC₃N in the region irradiated by the strong UV radiation are occurring. Our results indicate that the vibrationally excited HC₃N lines can be used as a disk tracer of massive protostars at the HC H ii region stage, and the combination of these nitrile species will provide information of not only chemistry but also physical conditions of the disk structures.

DOI： 10.3847/1538-4357/ac69d1

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac69d1/pdf

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2629811

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

<title>Abstract</title>
We have analyzed Atacama Large Millimeter/submillimeter Array Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from <italic>cyclic</italic>-C₃H₂ (<italic>c</italic>-C₃H₂), H₂CO, CH₃OH, ¹³CO, C¹⁸O, and DCO⁺ have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, <italic>c</italic>-C₃H₂ is enhanced at the west side, relative to the IR source, whereas H₂CO and CH₃OH are abundant at the east side. In the field of Oph-emb9, moment 0 maps of the <italic>c</italic>-C₃H₂ lines show a peak at the eastern edge of the field of view, which is irradiated by the Herbig Be star. Moment 0 maps of CH₃OH and H₂CO show peaks farther from the bright star. We derive the <italic>N</italic>(<italic>c</italic>-C₃H₂)/<italic>N</italic>(CH₃OH) column density ratios at the peak positions of <italic>c</italic>-C₃H₂ and CH₃OH near each YSO, which are identified based on their moment 0 maps. The <italic>N</italic>(<italic>c</italic>-C₃H₂)/<italic>N</italic>(CH₃OH) ratio at the <italic>c</italic>-C₃H₂ peak is significantly higher than at the CH₃OH peak by a factor of ∼19 in Oph-emb9, while the difference in this column density ratio between these two positions is a factor of ∼2.6 in Oph-emb5. These differences are attributed to the efficiency of the photon-dominated region chemistry in Oph-emb9. The higher DCO⁺ column density and the detection of DCN in Oph-emb9 are also discussed in the context of UV irradiation flux.

DOI： 10.3847/1538-4357/ac214e

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac214e/pdf

Language：English   Publishing type：Research paper (scientific journal)  

We report our analyses of the multi-epoch (2015-2017) Atacama Large Millimeter/submillimeter Array (ALMA) archival data of the Class II binary system XZ Tau at Bands 3, 4, and 6. The millimeter dust-continuum images show compact, unresolved (r 15 au) circumstellar disks (CSDs) around the individual binary stars, XZ Tau A and B, with a projected separation of ∼39 au. The 12CO (2-1) emission associated with those CSDs traces the Keplerian rotations, whose rotational axes are misaligned with each other (P.A. ∼-5° for XZ Tau A and ∼130° for XZ Tau B). The similar systemic velocities of the two CSDs (VLSR ∼ 6.0 km s-1) suggest that the orbital plane of the binary stars is close to the plane of the sky. From the multi-epoch ALMA data, we have also identified the relative orbital motion of the binary. Along with the previous NIR data, we found that the elliptical orbit (e = - 0.742+0.034 0.025, = a 0. 172+0. 003 0. 002, and w = -54 .2+ 4 .7 2.0) is preferable to the circular orbit. Our results suggest that the two CSDs and the orbital plane of the XZ Tau system are all misaligned with each other, and possible mechanisms to produce such a configuration are discussed. Our analyses of the multi-epoch ALMA archival data demonstrate the feasibility of time-domain science with ALMA.

DOI： 10.3847/1538-4357/ac0dc3

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/abb810

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abb810/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/abe854

Scopus

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abe854/pdf

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/1538-4357/ab9b7c

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/1538-4357/ab7eb3

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/1538-4357/ab8065

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomical Society of Japan  

We present measurements of the thermal Sunyaev-Zel'dovich effect (SZE) toward SPT-CL J2334-4243 (the Phoenix galaxy cluster) at z = 0.597 by the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. The SZE is imaged at 5″ resolution (corresponding to the physical scale of 23 h-1 kpc) within 200 h-1kpc from the central galaxy, with the peak signal-to-noise ratio exceeding 11. Combined with the Chandra X-ray image, the ALMA SZE data further allow for non-parametric deprojection of electron temperature, density, and entropy. Our method can minimize contamination by the central active galactic nucleus and the X-ray absorbing gas within the cluster, both of which greatly affect the X-ray spectrum.We find no significant asymmetry or disturbance in the SZE image within the current measurement errors. The detected SZE signal shows much higher central concentration than other distant galaxy clusters and agrees well with the average pressure profile of local cool-core clusters. Unlike in typical clusters at any redshift, the gas temperature drops by at least a factor of 5 toward the center.We identify ~6 × 1011M⊙cool gas with temperature ~3 keV in the inner 20 h-1kpc. Taken together, our results imply that the gas is indeed cooling efficiently and nearly isobarically down to this radius in the Phoenix cluster.

DOI： 10.1093/pasj/psaa009

Scopus

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/ab5284

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/ab4818

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/ab29f8

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/2041-8213/ab212f

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/ab0d80

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

DOI： 10.1051/0004-6361/201834209

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aafb6c

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aaffda

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aaf857

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aaf6ab

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aaed42

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aadd9d

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aae153

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aadb93

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP  

DOI： 10.3847/1538-4357/aacf9b

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

DOI： 10.1051/0004-6361/201732195

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/aaa4c1

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

DOI： 10.1051/0004-6361/201730894

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/2041-8213/aa9701

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/1538-4357/aa8264

Publisher：Journal of Physics: Conference Series  

DOI： 10.1088/1742-6596/837/1/012009

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/1538-4357/aa6116

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics  

DOI： 10.3847/1538-4357/834/2/178

arXiv

Publisher：Memorie della Societa Astronomica Italiana - Journal of the Italian Astronomical Society  

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics  

DOI： 10.3847/1538-4357/833/1/55

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/0004-637X/832/2/204

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

DOI： 10.3847/0004-637X/831/1/90

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本天文学会  

We present the first image of the thermal Sunyaev-Zel'dovich effect (SZE) obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Combining 7-m and 12-m arrays in Band 3, we create an SZE map toward a galaxy cluster RX J1347.5-1145 with 5″ resolution (corresponding to a physical size of 20 h-1 kpc), the highest angular and physical spatial resolutions achieved to-date for imaging the SZE, while retaining extended signals out to 40″. The 1 σ statistical sensitivity of the image is 0.017 mJy beam-1 or 0.12 mKCMB at the 5″ full width at half maximum. The SZE image shows a good agreement with an electron pressure map reconstructed independently from the X-ray data and offers a new probe of the small-scale structure of the intracluster medium. Our results demonstrate that ALMA is a powerful instrument for imaging the SZE in compact galaxy clusters with unprecedented angular resolution and sensitivity. As the first report on the detection of the SZE by ALMA, we present detailed analysis procedures including corrections for the missing flux, to provide guiding methods for analyzing and interpreting future SZE images obtained by ALMA.

DOI： 10.1093/pasj/psw082

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

Both bulk rotation and local turbulence have been widely suggested to drive the fragmentation in collapsing cores that produces multiple star systems. Even when the two mechanisms predict different alignments for stellar spins and orbits, subsequent internal or external interactions can drive multiple systems toward or away from alignment, thus masking their formation processes. Here, we demonstrate that the geometrical and dynamical relationship between a binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel, not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 years indicate an orbital motion related to that of the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smaller than observed, the remaining solutions favor a circular or low-eccentricity orbit tilted by up to ˜25° from the circumstellar disks. Turbulence-driven fragmentation can generate local angular momentum to produce a coplanar binary system, but this would have no particular relationship to the system’s surrounding envelope. Instead, the observed properties conform with predictions for rotationally driven fragmentation. If the fragments were produced at different heights or on opposite sides of the mid-plane in the flattened central region of a rotating core, the resulting protostars would then exhibit circumstellar disks parallel with the surrounding envelope but tilted from the orbital plane, as is observed.

DOI： 10.3847/0004-637X/826/2/153

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

We have analyzed the HCO+ (1-0) data of the Class I-II protostar, HL Tau, obtained from the Atacama Large Millimeter/submillimeter Array long baseline campaign. We generated the HCO+ image cube at an angular resolution of ˜0.″07 (˜10 au) and performed azimuthal averaging on the image cube to enhance the signal-to-noise ratio and measure the radial profile of the HCO+ integrated intensity. Two gaps at radii of ˜28 and ˜69 au and a central cavity are identified in the radial intensity profile. The inner HCO+ gap is coincident with the millimeter continuum gap at a radius of 32 au. The outer HCO+ gap is located at the millimeter continuum bright ring at a radius of 69 au and overlaps with the two millimeter continuum gaps at radii of 64 and 74 au. On the contrary, the presence of the central cavity is likely due to the high optical depth of the 3 mm continuum emission and not the depletion of the HCO+ gas. We derived the HCO+ column density profile from its intensity profile. From the column density profile, the FWHM widths of the inner and outer HCO+ gaps are both estimated to be ˜14 au, and their depths are estimated to be ˜2.4 and ˜5.0. These results are consistent with the expectation from the gaps opened by forming (sub-)Jovian mass planets, while placing tight constraints on the theoretical models solely incorporating the variation of dust properties and grain sizes.

DOI： 10.3847/2041-8205/820/2/L25

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本天文学会  

Ground-based observations at terahertz (THz) frequencies are a newly explorable area of astronomy in the coming decades. We discuss science cases for a first-generation 10-m class THz telescope, focusing on the Greenland Telescope as an example of such a facility. We propose science cases and provide quantitative estimates for each case. The largest advantage of ground-based THz telescopes is their higher angular resolution (˜ 4″ for a 10-m dish), as compared to space or airborne THz telescopes. Thus, high-resolution mapping is an important scientific argument. In particular, we can isolate zones of interest for Galactic and extragalactic star-forming regions. The THz windows are suitable for observations of high-excitation CO lines and [N II] 205-μm lines, which are scientifically relevant tracers of star formation and stellar feedback. Those lines are the brightest lines in the THz windows, so they are suitable for the initiation of ground-based THz observations. THz polarization of star-forming regions can also be explored since it traces the dust population contributing to the THz spectral peak. For survey-type observations, we focus on "sub-THz" extragalactic surveys, the uniqueness of which is detecting galaxies at redshifts z ˜ 1-2, where the dust emission per comoving volume is the largest in the history of the Universe. Finally we explore possibilities of flexible time scheduling, which enables us to monitor active galactic nuclei, and to target gamma-ray burst afterglows. For these objects, THz and submillimeter wavelength ranges have not yet been explored.

DOI： 10.1093/pasj/psv115

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

We performed mapping observations of the Class I protostellar binary system L1551 NE in the C18O (J = 3-2), 13CO (J = 3-2), CS (J = 7-6), and SO (JN = 78-67) lines with the Atacama Submillimeter Telescope Experiment (ASTE). The ASTE C18O data were combined with our previous SMA C18O data, which show a r ˜ 300 AU scale Keplerian disk around the protostellar binary system. The C18O maps show a ˜20,000 AU scale protostellar envelope surrounding the central Keplerian circumbinary disk. The envelope exhibits a northeast (blue) to southwest (red) velocity gradient along the minor axis, which can be interpreted as a dispersing gas motion with an outward velocity of 0.3 km s-1, while no rotational motion in the envelope is seen. In addition to the envelope, two ≲4000 AU scale, high-velocity (≳1.3 km s-1) redshifted 13CO and CS emission components are found ˜40″ southwest and ˜20″ west of the protostellar binary. These redshifted components are most likely outflow components driven from the neighboring protostellar source L1551 IRS 5, and are colliding with the envelope in L1551 NE. The net momentum, kinetic, and internal energies of the L1551 IRS 5 outflow components are comparable to those of the L1551 NE envelope, and the interactions between the outflows and the envelope are likely to cause the dissipation of the envelope and thus suppression of further growth of the mass and mass ratio of the central protostellar binary in L1551 NE.

DOI： 10.1088/0004-637X/814/2/160

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

We report an 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 SubMillimeter Array (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.

DOI： 10.1088/0004-637X/796/1/1

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We report follow-up C18O(3-2) line observations of the Class I binary protostellar system L1551 NE with the Submillimeter Array 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, with more extensive spatial coverage (~140-2000 AU), verify the presence of a Keplerian circumbinary disk and reveal for the first time a distinct low-velocity (lsim ± 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. This velocity is significantly smaller than the expected free-fall velocity of ~2.2 km s-1 onto the L1551 NE protostellar mass of ~0.8 M ⊙ 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 the inner Keplerian circumbinary disk implies an abrupt transition in the effectiveness at which magnetic braking is able to transfer angular momentum outward, a result perhaps of the different plasma β values and the ionization fractions between the outer and inner regions of the circumbinary disk.

DOI： 10.1088/0004-637X/776/1/51

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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 × 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 × 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 M ⊙, compared with an enclosed mass of ~0.8 M ⊙ 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 M ⊙), 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.

DOI： 10.1088/0004-637X/754/1/52

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本天文学会  

We have made mapping observations of L 1551 IRS 5, L 1551 NE, L 723, and L 43 and single-point observations of IRAS 16293-2422 in the submillimeter CS (J ="> 7-6) and HCN (J = ;4-3) lines with Atacama Submillimeter Telescope Experiment (ASTE). Using the present data and our previous ASTE observations of L 483 and B 335 together, we found a definite correlation between source bolometric luminosities and total integrated intensities of the submillimeter lines (ICS ∝ Lbol0.92). The combined ASTE + Submillimeter Array CS (7-6) image of L 1551 IRS 5 exhibits an extended (˜2000 AU) component tracing the associated reflection nebula at west and southwest, as well as a compact (≲ 500 AU) component centered on the protostellar position. The peaks of the CS and HCN emissions in L 1551 NE are not located at the protostellar position but offset (˜1400 AU) toward the associated reflection nebula at west. By statistical analyses, we confirmed the velocity gradients of the CS (7-6) emission that are opposite 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±1.7) × 10-3 km s-1 arcsec-1 in L 1551 IRS 5 and (7.6±2.4) × 10-3 km s-1 arcsec-1 in L 483. We suggest that the ``skewed' submillimeter molecular emissions toward the associated reflection nebulae at a few thousand AU scale trace the warm (≳ 40 K) walls of the envelope cavities, excavated by the associated outflows and directly irradiated by the central protostars. The opposite velocity gradients along the outflow direction likely reflect the dispersing gas motion at the wall of the cavity in envelopes perpendicular to the outflow.

DOI： 10.1093/pasj/63.4.921

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We have observed dense gas around the Very Low Luminosity Objects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Toward 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 toward IRAM 04191+1522, and the abundances of the carbon-chain molecules toward L1521F-IRS are 2-5 times higher than those toward 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 toward 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 toward 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.

DOI： 10.1088/0004-637X/728/2/101

arXiv

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS ( J=7 6) and HCN ( J=4 3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ˜2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.

DOI： 10.1007/s10509-007-9617-2

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

With the Submillimeter Array (SMA) we have made high angular resolution (~1''=160 AU) observations of the protobinary system IRAS 16293-2422 in the HCN (4-3), HC15N (4-3), and 354.5 GHz continuum emission. The HCN (4-3) line was also observed using the JCMT to supply missing short-spacing information. The submillimeter continuum emission is detected from the individual binary components of source A in the southeast and source B in the northwest, with a separation of ~5". The optically thin HC15N (4-3) emission taken with the SMA has revealed a compact (~500 AU) flattened structure (P.A.=-16deg) at source A. This compact structure shows a velocity gradient along the projected minor axis, which can be interpreted as an infalling gas motion. Our HCN image including the short-spacing information shows an extended (~3000 AU) circumbinary envelope, as well as the compact structure at source A. A toy model consisting of a flattened structure with radial infall toward a 1 Msolar central star reproduces the HCN/HC15N position-velocity diagram along the minor axis of the HC15N emission. In the extended envelope there is also a northeast (blue) to southwest (red) velocity gradient across the binary alignment, which is likely to reflect gas motion in the swept-up dense gas associated with the molecular outflow from source A. Only a weak and narrow (~2 km s-1) compact HC15N emission is associated with source B, where no clear molecular outflow is identified, suggesting the different evolutionary starges between sources A and B. Our study demonstrates the importance of adding short-spacing data to interferometer data in order to probe the detailed structure and kinematics of low-mass protostellar envelopes.

DOI： 10.1086/513589

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本天文学会  

With the ASTE telescope, we have observed three low-mass protostellar envelopes around L483, B335, and L723 in the submillimeter CS (J = 7-6) and HCN (J = 4-3) lines. We detected both the CS and HCN lines toward all targets, and the typical CS intensity (˜ 1.0 K in TB) was twice higher than that of the HCN line. Mapping observations of L483 in these lines have shown that the submillimeter emissions are resolved, exhibit a western extension from the central protostar, and that the deconvolved size is ˜ 5500 AU × 3700 AU (PA = 78°) in the HCN emission. The extent of the submillimeter emission in L483 implies the presence of higher temperature (/gtrsim 40 K) gas at 4000 AU away from the central protostar, which suggests that we need to take 2-dimensional radiative transfer models with a bipolar cavity into account. The position-velocity diagrams of these submillimeter lines along the axis of the associated molecular outflow exhibit that the sense of the submillimeter velocity gradient is opposite to that of the millimeter observation or the associated molecular outflow, both in L483 and in B335. We suggest that expanding gas motions at the surface of the flattened envelope, which is irradiated by the central protostar directly, are the origin of the observed submillimeter velocity structure.

DOI： 10.1093/pasj/59.1.1

arXiv

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

We have imaged the circumstellar envelope around the binary protostar L1551 IRS 5 in CS J=7-6 and 343 GHz continuum emission at ~3" resolution using the Submillimeter Array. The continuum emission shows an elongated structure (~220×100 AU) around the binary perpendicular to the axis of the associated radio jet. The CS emission extends over ~400 AU, appears approximately circularly symmetric, and shows a velocity gradient from southeast (blueshifted) to northwest (redshifted). The direction of the velocity gradient is different from that observed in C18O J=1-0. This may be because rotation is more dominant in the CS envelope than the C18O envelope, in which both infall and rotation exist. The CS emission can be divided into two velocity components: (1) a ``high'-velocity disklike structure surrounding the protostar +/-1.0-1.5 km s-1 from the systemic velocity, and (2) a ``low'-velocity structure located southwest of the protostar less than 1.0 km s-1 from the systemic velocity. The high-velocity component traces warm and dense gas with kinematics consistent with rotation around the protostar. The low-velocity component may arise from dense gas entrained in the outflow. Alternatively, this component may trace infalling and rotating gas in an envelope with a vertical structure.

DOI： 10.1086/421939

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The American Astronomical Society  

We have carried out mapping observations of the molecular core associated with the young Class 0 protostar, IRAM 04191+1522, in the CH3OH (JK=2K-1K) and C34S (J=2-1) lines, using the 45 m telescope at Nobeyama Radio Observatory. Our observations have revealed that there is a condensation associated with the protostar, elongated in the east-west direction mostly perpendicular to the axis of the associated CO outflow. Its size and mass are estimated to be 0.07×0.04 pc and 2.3 Msolar, respectively, from the CH3OH data. In addition to the elongated envelope, two compact (~0.03 pc) condensations were found in the CH3OH line at the southern edge of the elongated envelope, where the blueshifted CO outflow emerging from the protostar is located. In contrast to the elongated envelope, those compact CH3OH condensations show much larger line width (up to 2.0 km s-1), with centroid velocities blueshifted by ~0.8 km s-1. The compact condensations have momenta (~0.06 Msolar km s-1) comparable to that of the blueshifted molecular outflow. In addition, they are gravitationally unbound, and most probably will dissipate eventually. These results suggest that the compact condensations are probably formed in the course of interaction between the outflow and the ambient gas surrounding the protostar and that such interaction may cause dissipation of a part of the ambient gas. No drastic, localized enhancement of the CH3OH abundance is, however, observed toward the compact condensations, implying that there seems to be no significant shock heating at the compact condensations, in spite of the interaction with the outflow. This may be because the CO outflow velocity (<10 km s-1) is too low to cause effective heating to release CH3OH on dust grains into the gas phase.

DOI： 10.1086/375190

arXiv

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We have carried out detailed H13CO+ (J=1-0) and CH3OH (JK=20-10 A+) observations of two dense cores in the TMC-1C region with the 45 m telescope at Nobeyama Radio Observatory and the Nobeyama Millimeter Array (NMA). These two cores, H13CO+ core 2 and CH3OH core 6, were identified previously by the H13CO+ and CH3OH mapping observations of the entire TMC-1C region and show no sign of protostar formation. We found that the internal structure of H13CO+ core 2 is different from that of cores with class 0 protostars; this core consists of three velocity components and shows the radial column density distribution of ~r-0.43+/-0.08, which is flatter than that in the protostellar cores (~r-1.0). The internal structure of CH3OH core 6 is different from that of H13CO+ core 2; the combined images of the 45 m and NMA data have revealed that there are three smaller scale CH3OH ``clumps'' ~2500 AU in size inside this core. The mass of the small-scale clumps, ~0.02 Msolar, is much smaller than the virial mass (~0.3 Msolar), suggesting that these clumps are gravitationally unbound. The velocity dispersion observed in these small-scale clumps is 0.45-0.5 km s-1, which is comparable to that of clumps with 0.02-0.03 pc in radius. A comparison of the velocity dispersion of the small-scale clumps and that of larger scale cores suggests that the velocity dispersion that follows the power law in the radius larger than ~0.02-0.03 pc turns into a constant value of ~0.45-0.5 km s-1 in the smaller size scale. The mass-size relation of the prestellar gas structures suggests that they follow the trend of constant gas density (~105 cm-3) in the radius from 0.006 to ~0.3 pc and that the smaller scale structures tend to be gravitationally unbound. The presence of the small clumps with substellar masses in prestellar cores implies that coalescence processes are likely to play an important role in forming protostars inside the cores. The observational difference of the internal structures among CH3OH core 6, H13CO+ core 2, and protostellar cores might represent the difference of the evolutionary stages.

DOI： 10.1086/345845

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本天文学会  

We have observed cyclic C3H2 (JKaKc = 212-101, 202 - 111, 312 - 303) lines at the 3 mm wavelength region toward the starless TMC-1C cloud and the protostellar core of L 1527 with the 45 m telescope at Nobeyama Radio Observatory. In both clouds, the 212-101 and 202 - 111 lines are strongly detected, while the 312 - 303 line is only detected toward the center of the protostellar core L 1527. From our statistical equilibrium analyses of the ortho-C3H2(212-101) and the para-C3H2(202-111)lines, the ortho-to-para ratios of C3H2 are determined to be 2.4 +/- 0.1 and 2.5 +/- 0.5 in TMC-1C and L 1527, respectively. These values are lower than the statistical value of 3, although the error of the ratio in L 1527 is large. Since thermal equilibrium with a dust temperature of 10 K still gives a ratio of 3 in c-C3H2, this result should suggest the lower ortho-to-para ratio of the precursor molecule, c-C3H+3, which is thought to be mainly produced by C3H++H2. Thus, we conclude that the lower ortho-to-para ratio of c-C3H2 is due to a lower ortho-to-para ratio of H2 than the statistical value.

DOI： 10.1093/pasj/53.2.251

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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.

DOI： 10.1086/309505

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We have mapped the entire TMC-1C region in the H13CO+ (J = 1-0) and CH3OH (JK = 20-10A+) lines at a grid spacing of 50" with the 45 m telescope at Nobeyama Radio Observatory. We have also conducted high spatial resolution mapping observations of the TMC-1C region at a grid spacing of 34" in both lines toward a 6' × 6' portion in the south and a 4' × 4' portion in the north. We found that the structure of TMC-1C is filamentary in both molecular lines. The size and position angle of the filament are 0.75 pc × 0.17 pc and 135°, respectively. The filament consists of dense (~105 cm-3) cores which are traced by either H13CO+ or CH3OH lines. We found that the distribution of cores seen in H13CO+ is quite different from the distribution of cores seen in CH3OH. The large velocity gradient analyses indicate that this difference is a result of the relative abundance variation between H13CO+ and CH3OH in the cores by about 1 order of magnitude. We have also carried out multitransitional observations of C3H2 (JK',K'' = 21,2-10,1 and 31,2-30,3) at two positions in the same cloud in order to estimate the molecular hydrogen densities for H13CO+ and CH3OH cores and found that the densities are around 105 cm-3 for both cores. These starless cores (no IRAS source), considered to be prestellar cores, seem to be at chemically different evolutionary stages; the H13CO+ cores are more evolved and closer to protostar formation than CH3OH cores. On the other hand, we found no difference in physical properties, i.e., the size, line width, and mass, between H13CO+ and CH3OH cores; the averages are about 0.07 pc, 0.3 km s-1, and 2 M⊙, respectively.

DOI： 10.1086/305855