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

arXiv

Other Link： http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009ApJ...703.1198F&link_type=EJOURNAL&db_key=AST&high=

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

arXiv

Other Link： http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009ApJ...698.1924S&link_type=EJOURNAL&db_key=AST&high=

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

arXiv

Other Link： http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008ApJ...682.1103S&link_type=EJOURNAL&db_key=AST&high=

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

We used the Submillimeter Array to image the SiO maser emission in the $v=1$,
\$J=5-4$ transition associated with the peculiar red supergiant VY Canis
Majoris. We identified seven maser components and measured their relative
positions and linear polarization properties. Five of the maser components are
coincident to within about 150 mas ($\sim$ 200 AU at the distance of 1.5 kpc);
most of them may originate in the circumstellar envelope at a radius of about
50 mas from the star along with the SiO masers in the lowest rotational
transitions. Our measurements show that two of the maser components may be
offset from the inner stellar envelope (at the 3$\sigma$ level of significance)
and may be part of a larger bipolar outflow associated with VY CMa identified
by Shinnaga et al. The strongest maser feature at a velocity of 35.9 kms$^{-1}$
has a 60 percent linear polarization, and its polarization direction is aligned
with the bipolar axis. Such a high degree of polarization suggests that maser
inversion is due to radiative pumping. Five of the other maser features have
significant linear polarization.

DOI： 10.1086/425133

arXiv

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Other Link： http://arxiv.org/pdf/astro-ph/0408298v2

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

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

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

We have designed and constructed a tunable polarimeter to cover frequencies from 35 GHz to 250 GHz (8.6 mm and 1.2 mm in wavelength) for the 45-m telescope at Nobeyama Radio Observatory. Both circular and linear polarizations can be measured by the polarimeter. The insertion loss was measured to be 0.14 ± 0.05 dB in the 100-GHz band. The overall instrumental polarization of the system in the 100 GHz band is as low as ≤ 3%. The performance of the polarimeter in astronomical observations was tested by simultaneously measuring the linear polarization of the J = 2-1 transition of SiO in the v = 0 and 1 states at 86 GHz toward VY Canis Majoris. The observation revealed that the J = 2-1 emission in the v = 0 state of the object is highly linear polarized, which suggests that the emission originates through maser action in the circumstellar region. The details of the design, construction, and tests are presented.

DOI： 10.1093/pasj/51.2.175

Scopus

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

Zeeman splittings of the rotational transitions of the CCS and SO radicals in the 3Σ- ground electronic state have been calculated. Since the coupling scheme of the rotational angular momentum and the electron-spin angular momentum is intermediate between Hund's cases (a) and (b), the mixing between the F1 and F3 levels has been treated strictly. In order to confirm the calculation, Zeeman splittings of the JN = 43-32 and JN = 32-21 lines of CCS are measured by laboratory microwave spectroscopy. The effective g-factors evaluated in the present study are of particular importance in the determination of the magnetic field strength of dense cores through polarization observations.

DOI： 10.1086/317212

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/pasj/psae062

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Language：English   Publishing type：Research paper (other academic)  

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

Abstract

We present BISTRO Survey 850 μm dust emission polarization observations of the L1495A-B10 region of the Taurus molecular cloud, taken at the James Clerk Maxwell Telescope (JCMT). We observe a roughly triangular network of dense filaments. We detect nine of the dense starless cores embedded within these filaments in polarization, finding that the plane-of-sky orientation of the core-scale magnetic field lies roughly perpendicular to the filaments in almost all cases. We also find that the large-scale magnetic field orientation measured by Planck is not correlated with any of the core or filament structures, except in the case of the lowest-density core. We propose a scenario for early prestellar evolution that is both an extension to, and consistent with, previous models, introducing an additional evolutionary transitional stage between field-dominated and matter-dominated evolution, observed here for the first time. In this scenario, the cloud collapses first to a sheet-like structure. Uniquely, we appear to be seeing this sheet almost face on. The sheet fragments into filaments, which in turn form cores. However, the material must reach a certain critical density before the evolution changes from being field dominated to being matter dominated. We measure the sheet surface density and the magnetic field strength at that transition for the first time and show consistency with an analytical prediction that had previously gone untested for over 50 yr.

DOI： 10.3847/1538-4357/acbea4

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acbea4/pdf

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

Abstract

We study the Hii regions associated with the NGC 6334 molecular cloud observed in the submillimeter and taken as part of the B-fields In STar-forming Region Observations Survey. In particular, we investigate the polarization patterns and magnetic field morphologies associated with these Hii regions. Through polarization pattern and pressure calculation analyses, several of these bubbles indicate that the gas and magnetic field lines have been pushed away from the bubble, toward an almost tangential (to the bubble) magnetic field morphology. In the densest part of NGC 6334, where the magnetic field morphology is similar to an hourglass, the polarization observations do not exhibit observable impact from Hii regions. We detect two nested radial polarization patterns in a bubble to the south of NGC 6334 that correspond to the previously observed bipolar structure in this bubble. Finally, using the results of this study, we present steps (incorporating computer vision; circular Hough transform) that can be used in future studies to identify bubbles that have physically impacted magnetic field lines.

DOI： 10.3847/1538-4357/acac81

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acac81/pdf

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

DOI： 10.3847/1538-4357/acd6f2

Other Link： http://arxiv.org/abs/2305.11306v2

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

We present 850 $\mu$m dust polarization observations of the massive DR21
filament from the B-fields In STar-forming Region Observations (BISTRO) survey,
using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell
Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale
ridge of the DR21 main filament. In the sub-filaments, the magnetic fields are
mainly parallel to the filamentary structures and smoothly connect to the
magnetic fields of the main filament. We compare the POL-2 and Planck dust
polarization observations to study the magnetic field structures of the DR21
filament on 0.1--10 pc scales. The magnetic fields revealed in the Planck data
are well aligned with those of the POL-2 data, indicating a smooth variation of
magnetic fields from large to small scales. The plane-of-sky magnetic field
strengths derived from angular dispersion functions of dust polarization are
0.6--1.0 mG in the DR21 filament and $\sim$ 0.1 mG in the surrounding ambient
gas. The mass-to-flux ratios are found to be magnetically supercritical in the
filament and slightly subcritical to nearly critical in the ambient gas. The
alignment between column density structures and magnetic fields changes from
random alignment in the low-density ambient gas probed by Planck to mostly
perpendicular in the high-density main filament probed by JCMT. The magnetic
field structures of the DR21 filament are in agreement with MHD simulations of
a strongly magnetized medium, suggesting that magnetic fields play an important
role in shaping the DR21 main filament and sub-filaments.

DOI： 10.3847/1538-4357/ac9dfb

arXiv

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Other Link： http://arxiv.org/pdf/2212.01981v1

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

DOI： 10.23919/apmc55665.2022.9999827

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

We present and analyze observations of polarized dust emission at 850 $\mu$m
towards the central 1 pc $\times$ 1 pc hub-filament structure of Monoceros R2
(Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell
Telescope (JCMT) as part of the BISTRO (B-fields in Star-forming Region
Observations) survey. The orientations of the magnetic field follow the spiral
structure of Mon R2, which are well-described by an axisymmetric magnetic field
model. We estimate the turbulent component of the magnetic field using the
angle difference between our observations and the best-fit model of the
underlying large-scale mean magnetic field. This estimate is used to calculate
the magnetic field strength using the Davis-Chandrasekhar-Fermi method, for
which we also obtain the distribution of volume density and velocity dispersion
using a column density map derived from $Herschel$ data and the C$^{18}$O ($J$
= 3-2) data taken with HARP on the JCMT, respectively. We make maps of magnetic
field strengths and mass-to-flux ratios, finding that magnetic field strengths
vary from 0.02 to 3.64 mG with a mean value of 1.0 $\pm$ 0.06 mG, and the mean
critical mass-to-flux ratio is 0.47 $\pm$ 0.02. Additionally, the mean Alfv\'en
Mach number is 0.35 $\pm$ 0.01. This suggests that in Mon R2, magnetic fields
provide resistance against large-scale gravitational collapse, and magnetic
pressure exceeds turbulent pressure. We also investigate the properties of each
filament in Mon R2. Most of the filaments are aligned along the magnetic field
direction and are magnetically sub-critical.

DOI： 10.3847/1538-4357/ac99e0

arXiv

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Other Link： http://arxiv.org/pdf/2210.05937v4

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

The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of ∼850 Galactic evolved stars within 3 kpc at (sub-)mm wavelengths, observed in the CO J = (2-1) and (3-2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a new metric for estimating the distances to evolved stars and compare its results to Gaia EDR3. Replicating other studies, the most-evolved, highly enshrouded objects in the Galactic Plane dominate the dust returned by our sources, and we initially estimate a total DPR of 4.7 × 10-5 M⊙ yr-1 from our sample. Our sub-mm fluxes are systematically higher and spectral indices are typically shallower than dust models typically predict. The 450/850 μm spectral indices are consistent with the blackbody Rayleigh-Jeans regime, suggesting a large fraction of evolved stars have unexpectedly large envelopes of cold dust.

DOI： 10.1093/mnras/stab2860

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

Polarized dust emission is a key tracer in the study of interstellar medium and of star formation. The observed polarization, however, is a product of magnetic field structure, dust grain properties, and grain alignment efficiency, as well as their variations in the line of sight, making it difficult to interpret polarization unambiguously. The comparison of polarimetry at multiple wavelengths is a possible way of mitigating this problem. We use data from HAWC+ /SOFIA and from SCUBA-2/POL-2 (from the BISTRO survey) to analyse the NGC 2071 molecular cloud at 154, 214, and 850 $\mu$m. The polarization angle changes significantly with wavelength over part of NGC 2071, suggesting a change in magnetic field morphology on the line of sight as each wavelength best traces different dust populations. Other possible explanations are the existence of more than one polarization mechanism in the cloud or scattering from very large grains. The observed change of polarization fraction with wavelength, and the 214-To-154 $\mu$m polarization ratio in particular, are difficult to reproduce with current dust models under the assumption of uniform alignment efficiency. We also show that the standard procedure of using monochromatic intensity as a proxy for column density may produce spurious results at HAWC+wavelengths. Using both long-wavelength (POL-2, 850 $\mu$m) and short-wavelength (HAWC+, $\lesssim 200\, \mu$m) polarimetry is key in obtaining these results. This study clearly shows the importance of multi-wavelength polarimetry at submillimetre bands to understand the dust properties of molecular clouds and the relationship between magnetic field and star formation.

DOI： 10.1093/mnras/stac528

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

We present 850 $\mu$m polarimetric observations toward the Serpens Main
molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell
Telescope (JCMT) as part of the B-fields In STar-forming Region Observations
(BISTRO) survey. These observations probe the magnetic field morphology of the
Serpens Main molecular cloud on about 6000 au scales, which consists of cores
and six filaments with different physical properties such as density and star
formation activity. Using the histogram of relative orientation (HRO)
technique, we find that magnetic fields are parallel to filaments in less dense
filamentary structures where $N_{H_2} < 0.93\times 10^{22}$ cm$^{-2}$ (magnetic
fields perpendicular to density gradients), while being perpendicular to
filaments (magnetic fields parallel to density gradients) in dense filamentary
structures with star formation activity. Moreover, applying the HRO technique
to denser core regions, we find that magnetic field orientations change to
become perpendicular to density gradients again at $N_{H_2} \approx 4.6 \times
10^{22}$ cm$^{-2}$. This can be interpreted as a signature of core formation.
At $N_{H_2} \approx 16 \times 10^{22}$ cm$^{-2}$ magnetic fields change back to
being parallel to density gradients once again, which can be understood to be
due to magnetic fields being dragged in by infalling material. In addition, we
estimate the magnetic field strengths of the filaments ($B_{POS} =
60-300~\mu$G)) using the Davis-Chandrasekhar-Fermi method and discuss whether
the filaments are gravitationally unstable based on magnetic field and
turbulence energy densities.

DOI： 10.3847/1538-4357/ac4bbe

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arXiv

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Other Link： http://arxiv.org/pdf/2201.05059v1

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

DOI： 10.3847/1538-4357/ac551f

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

We present the results of simultaneous 450 $\mu$m and 850 $\mu$m polarization
observations toward the massive star forming region NGC 2071IR, a target of the
BISTRO (B-fields in Star-Forming Region Observations) Survey, using the POL-2
polarimeter and SCUBA-2 camera mounted on the James Clerk Maxwell Telescope. We
find a pinched magnetic field morphology in the central dense core region,
which could be due to a rotating toroidal disk-like structure and a bipolar
outflow originating from the central young stellar object, IRS 3. Using the
modified Davis-Chandrasekhar-Fermi method, we obtain a plane-of-sky magnetic
field strength of 563$\pm$421 $\mu$G in the central $\sim$0.12 pc region from
850 $\mu$m polarization data. The corresponding magnetic energy density of
2.04$\times$10$^{-8}$ erg cm$^{-3}$ is comparable to the turbulent and
gravitational energy densities in the region. We find that the magnetic field
direction is very well aligned with the whole of the IRS 3 bipolar outflow
structure. We find that the median value of polarization fractions, 3.0 \%, at
450 $\mu$m in the central 3 arcminute region, which is larger than the median
value of 1.2 \% at 850 $\mu$m. The trend could be due to the better alignment
of warmer dust in the strong radiation environment. We also find that
polarization fractions decrease with intensity at both wavelengths, with
slopes, determined by fitting a Rician noise model, of $0.59 \pm 0.03$ at 450
$\mu$m and $0.36 \pm 0.04$ at 850 $\mu$m, respectively. We think that the
shallow slope at 850 $\mu$m is due to grain alignment at the center being
assisted by strong radiation from the central young stellar objects.

DOI： 10.3847/1538-4357/ac0ce9

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arXiv

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Other Link： http://arxiv.org/pdf/2109.13543v1

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

DOI： 10.3847/1538-4357/abee1e

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abee1e/pdf

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

In the published article, we presented high-resolution polarimetry data obtained by using JCMT SCUBA-2/POL-2, and compared them with the larger-scale magnetic structure observed by Planck (Planck Collaboration et al. 2020). There was a miscalculation in the analysis of the Planck data for comparison, and the mean position angle of the Planck magnetic field should be corrected from -40° ± 7° to -48° ± 6°. Thus, we replace the descriptions in the published article as follows. In Section 4.2, paragraph 3, the second sentence should read: "The differences between the orientations of IRAS 4A, IRAS 4B, and IRAS 2A are not statistically significant, but they do show significantly different orientations from those of the global B-field observed by Planck (-48° ± 6°
Section 4.1)." In Section 4.1, paragraph 3, the second line should read: "The Planck B-field orientation shows a smoothly and slowly varying field distribution with a position angle of -48° ± 6° in our observed NGC 1333 area." Accordingly, we replace Figures 4, 5, 9, 10, and 17 to reflect the correct Planck data. As described above, this error of modest magnitude is related only to our derivation of the Planck polarization angle, and the JCMT observation results are unaffected. Therefore, all conclusions drawn in the published article are unchanged even after the above correction is applied. The 1 pc scale magnetic field observed by Planck shows a smooth distribution, and the interstellar magnetic field in molecular clouds increases the complexity significantly on the scale of less than 1 pc.

DOI： 10.3847/1538-4357/abf2b3

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

We have obtained sensitive dust continuum polarization observations at 850
$\mu$m in the B213 region of Taurus using POL-2 on SCUBA-2 at the James Clerk
Maxwell Telescope (JCMT), as part of the BISTRO (B-fields in STar-forming
Region Observations) survey. These observations allow us to probe magnetic
field (B-field) at high spatial resolution ($\sim$2000 au or $\sim$0.01 pc at
140 pc) in two protostellar cores (K04166 and K04169) and one prestellar core
(Miz-8b) that lie within the B213 filament. Using the Davis-Chandrasekhar-Fermi
method, we estimate the B-field strengths in K04166, K04169, and Miz-8b to be
38$\pm$14 $\mu$G, 44$\pm$16 $\mu$G, and 12$\pm$5 $\mu$G, respectively. These
cores show distinct mean B-field orientations. B-field in K04166 is well
ordered and aligned parallel to the orientations of the core minor axis,
outflows, core rotation axis, and large-scale uniform B-field, in accordance
with magnetically regulated star formation via ambipolar diffusion taking place
in K04166. B-field in K04169 is found to be ordered but oriented nearly
perpendicular to the core minor axis and large-scale B-field, and not
well-correlated with other axes. In contrast, Miz-8b exhibits disordered
B-field which show no preferred alignment with the core minor axis or
large-scale field. We found that only one core, K04166, retains a memory of the
large-scale uniform B-field. The other two cores, K04169 and Miz-8b, are
decoupled from the large-scale field. Such a complex B-field configuration
could be caused by gas inflow onto the filament, even in the presence of a
substantial magnetic flux.

DOI： 10.3847/2041-8213/abeb1c

arXiv

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Other Link： http://arxiv.org/pdf/2103.02219v1

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

<italic>Context.</italic> Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained.


<italic>Aims.</italic> We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation.


<italic>Methods.</italic> We present new observations of the dust polarized emission at 850 <italic>μ</italic>m toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with the <italic>James Clerk Maxwell</italic> Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (<italic>PI</italic>), the polarization fraction (<italic>PF</italic>), and the plane-of-the-sky B-field angle (<italic>χ</italic>_{B_POS}) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and <italic>χ</italic>_{B_POS} along the ridge crest and compared them with the results obtained from simulated filaments.


<italic>Results.</italic> The observations span ~3 orders of magnitude in Stokes <italic>I</italic> and <italic>PI</italic> and ~2 orders of magnitude in <italic>PF</italic> (from ~0.2 to ~ 20%). A large scatter in <italic>PI</italic> and <italic>PF</italic> is observed for a given value of <italic>I</italic>. Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc), <italic>χ</italic>_{B_POS} varies coherently along the crests of the filament network. The observed power spectrum of <italic>χ</italic>_{B_POS} can be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that of <italic>I</italic>. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, <italic>χ</italic>_{B_POS} rotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in <italic>PF</italic> toward the high-column density (<italic>N</italic>_H₂ ≳ 10²³ cm⁻²) star cluster-forming hubs. These latter large <italic>PF</italic> values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure.


<italic>Conclusions.</italic> These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.

DOI： 10.1051/0004-6361/202038624

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

While magnetic fields likely play an important role in driving the evolution
of protoplanetary disks through angular momentum transport, observational
evidence of magnetic fields has only been found in a small number of disks.
Although dust continuum linear polarization has been detected in an increasing
number of disks, its pattern is more consistent with that from dust scattering
than from magnetically aligned grains in the vast majority of cases. Continuum
linear polarization from dust grains aligned to a magnetic field can reveal
information about the magnetic field's direction, but not its strength. On the
other hand, observations of circular polarization in molecular lines produced
by Zeeman splitting offer a direct measure of the line-of-sight magnetic field
strength in disks. We present upper limits on the net toroidal and vertical
magnetic field strengths in the protoplanetary disk AS 209 derived from Zeeman
splitting observations of the CN 2-1 line. The 3$\sigma$ upper limit on the net
line-of-sight magnetic field strength in AS 209 is 5.0 mG on the redshifted
side of the disk and 4.2 mG on the blueshifted side of the disk. Given the
disk's inclination angle, we set a 3$\sigma$ upper limit on the net toroidal
magnetic field strength of 8.7 and 7.3 mG for the red and blue sides of the
disk, respectively, and 6.2 and 5.2 mG on the net vertical magnetic field on
the red and blue sides of the disk. If magnetic disk winds are a significant
mechanism of angular momentum transport in the disk, magnetic fields of a
strength close to the upper limits would be sufficient to drive accretion at
the rate previously inferred for regions near the protostar.

DOI： 10.3847/1538-4357/abd94e

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arXiv

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Other Link： http://arxiv.org/pdf/2101.01846v1

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

We present the results of on-the-fly mapping observations of 44 fields
containing 107 SCUBA-2 cores in the emission lines of molecules, N$_2$H$^+$,
HC$_3$N, and CCS at 82$-$94 GHz using the Nobeyama 45-m telescope. This study
aimed at investigating the physical properties of cores that show high
deuterium fractions and might be close to the onset of star formation. We found
that the distributions of the N$_2$H$^+$ and HC$_3$N line emissions are
approximately similar to that of 850-$\mu$m dust continuum emission, whereas
the CCS line emission is often undetected or is distributed in a clumpy
structure surrounding the peak position of the 850-$\mu$m dust continuum
emission. Occasionally (12%), we observe the CCS emission which is an
early-type gas tracer toward the young stellar object, probably due to local
high excitation. Evolution toward star formation does not immediately affect
nonthermal velocity dispersion.

DOI： 10.3847/1538-4365/ac0978

arXiv

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Other Link： http://arxiv.org/pdf/2106.04052v1

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

We report the first high spatial resolution measurement of magnetic fields
surrounding LkH$\alpha$ 101, a part of the Auriga-California molecular cloud.
The observations were taken with the POL-2 polarimeter on the James Clerk
Maxwell Telescope within the framework of the B-fields In Star-forming Region
Observations (BISTRO) survey. Observed polarization of thermal dust emission at
850 $\mu$m is found to be mostly associated with the red-shifted gas component
of the cloud. The magnetic field displays a relatively complex morphology. Two
variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure
function, are used to calculate the strength of magnetic fields in the plane of
the sky, yielding a similar result of $B_{\rm POS}\sim 115$ $\mathrm{\mu}$G.
The mass-to-magnetic-flux ratio in critical value units, $\lambda\sim0.3$, is
the smallest among the values obtained for other regions surveyed by POL-2.
This implies that the LkH$\alpha$ 101 region is sub-critical and the magnetic
field is strong enough to prevent gravitational collapse. The inferred $\delta
B/B_0\sim 0.3$ implies that the large scale component of the magnetic field
dominates the turbulent one. The variation of the polarization fraction with
total emission intensity can be fitted by a power-law with an index of
$\alpha=0.82\pm0.03$, which lies in the range previously reported for molecular
clouds. We find that the polarization fraction decreases rapidly with proximity
to the only early B star (LkH$\alpha$ 101) in the region. The magnetic field
tangling and the joint effect of grain alignment and rotational disruption by
radiative torques are potential of explaining such a decreasing trend.

DOI： 10.3847/1538-4357/abd0fc

arXiv

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Other Link： http://arxiv.org/pdf/2012.04297v1

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

We compare the directions of molecular outflows of 62 low-mass Class 0 and I
protostars in nearby (<450 pc) star-forming regions with the mean orientations
of the magnetic fields on 0.05-0.5 pc scales in the dense cores/clumps where
they are embedded. The magnetic field orientations were measured using the JCMT
POL-2 data taken by the BISTRO-1 survey and from the archive. The outflow
directions were observed with interferometers in the literature. The observed
distribution of the angles between the outflows and the magnetic fields peaks
between 15 and 35 degrees. After considering projection effects, our results
could suggest that the outflows tend to be misaligned with the magnetic fields
by 50+/-15 degrees in three-dimensional space and are less likely (but not
ruled out) randomly oriented with respect to the magnetic fields. There is no
correlation between the misalignment and the bolometric temperatures in our
sample. In several sources, the small-scale (1000-3000 au) magnetic fields is
more misaligned with the outflows than their large-scale magnetic fields,
suggesting that the small-scale magnetic field has been twisted by the
dynamics. In comparison with turbulent MHD simulations of core formation, our
observational results are more consistent with models in which the energy
densities in the magnetic field and the turbulence of the gas are comparable.
Our results also suggest that the misalignment alone cannot sufficiently reduce
the efficiency of magnetic braking to enable formation of the observed number
of large Keplerian disks with sizes larger than 30-50 au.

DOI： 10.3847/1538-4357/abca99

arXiv

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Other Link： http://arxiv.org/pdf/2011.06731v1

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

Theoretical and numerical works indicate that a strong magnetic field should
suppress fragmentation in dense cores. However, this has never been tested
observationally in a relatively large sample of fragmenting massive dense
cores. Here we use the polarization data obtained in the Submillimeter Array
Legacy Survey of Zhang et al. (2014) to build a sample of 17 massive dense
cores where both fragmentation and magnetic field properties are studied in a
uniform way. We measured the fragmentation level, Nmm, within the field of view
common to all regions, of ~0.15 pc, with a mass sensitivity of ~0.5 Msun, and a
spatial resolution of ~1000 AU. In order to obtain the magnetic field strength
using the Davis-Chandrasekhar-Fermi method, we estimated the dispersion of the
polarization position angles, the velocity dispersion of the H13CO+(4-3) gas,
and the density of each core, all averaged within 0.15 pc. The magnetic field
strength was also inferred using the Angular Dispersion Function method.
Surprisingly, we found no apparent relation between the fragmentation level and
the magnetic field strength, while a possible trend of Nmm with the average
density of the parental core was found. In addition, the average masses of the
fragments are comparable to the thermal Jeans mass. Therefore, our results
suggest that thermal fragmentation and gravity dominate the fragmentation
process in this sample. However, when only cores with similar densities are
considered, there are hints of a possible anticorrelation between the
fragmentation level and the magnetic field strength.

arXiv

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Other Link： http://arxiv.org/pdf/2010.12099v1

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

We present the results of a single-pointing survey of 207 dense cores
embedded in Planck Galactic Cold Clumps distributed in five different
environments ($\lambda$ Orionis, Orion A, B, Galactic plane, and high
latitudes) to identify dense cores on the verge of star formation for the study
of the initial conditions of star formation. We observed these cores in eight
molecular lines at 76-94 GHz using the Nobeyama 45-m telescope. We find that
early-type molecules (e.g., CCS) have low detection rates and that late-type
molecules (e.g., N$_2$H$^+$, c-C$_3$H$_2$) and deuterated molecules (e.g.,
N$_2$D$^+$, DNC) have high detection rates, suggesting that most of the cores
are chemically evolved. The deuterium fraction (D/H) is found to decrease with
increasing distance, indicating that it suffers from differential beam dilution
between the D/H pair of lines for distant cores ($>$1 kpc). For $\lambda$
Orionis, Orion A, and B located at similar distances, D/H is not significantly
different, suggesting that there is no systematic difference in the observed
chemical properties among these three regions. We identify at least eight high
D/H cores in the Orion region and two at high latitudes, which are most likely
to be close to the onset of star formation. There is no clear evidence of the
evolutionary change in turbulence during the starless phase, suggesting that
the dissipation of turbulence is not a major mechanism for the beginning of
star formation as judged from observations with a beam size of 0.04 pc.

DOI： 10.3847/1538-4365/aba746

arXiv

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Other Link： http://arxiv.org/pdf/2007.12319v1

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

We present new observations of the active star-formation region NGC 1333 in
the Perseus molecular cloud complex from the James Clerk Maxwell Telescope
B-Fields In Star-forming Region Observations (BISTRO) survey with the POL-2
instrument. The BISTRO data cover the entire NGC 1333 complex (~1.5 pc x 2 pc)
at 0.02 pc resolution and spatially resolve the polarized emission from
individual filamentary structures for the first time. The inferred magnetic
field structure is complex as a whole, with each individual filament aligned at
different position angles relative to the local field orientation. We combine
the BISTRO data with low- and high- resolution data derived from Planck and
interferometers to study the multiscale magnetic field structure in this
region. The magnetic field morphology drastically changes below a scale of ~1
pc and remains continuous from the scales of filaments (~0.1 pc) to that of
protostellar envelopes (~0.005 pc or ~1000 au). Finally, we construct simple
models in which we assume that the magnetic field is always perpendicular to
the long axis of the filaments. We demonstrate that the observed variation of
the relative orientation between the filament axes and the magnetic field
angles are well reproduced by this model, taking into account the projection
effects of the magnetic field and filaments relative to the plane of the sky.
These projection effects may explain the apparent complexity of the magnetic
field structure observed at the resolution of BISTRO data toward the filament
network.

DOI： 10.3847/1538-4357/aba1e2

arXiv

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Other Link： http://arxiv.org/pdf/2007.00176v2

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

This white paper discusses recent progress in the field of evolved stars,
primarily highlighting the contributions of the James Clerk Maxwell Telescope.
It discusses the ongoing project, the \emph{Nearby Evolved Stars Survey}
(NESS), and the potential to build upon NESS in the next decade. It then
outlines a number of science cases which may become feasible with the proposed
850\,$\mu$m camera which is due to become available at the JCMT in late 2022.
These include mapping the extended envelopes of evolved stars, including in
polarisation, and time-domain monitoring of their variations. The improved
sensitivity of the proposed instrument will facilitate statistical studies that
put the morphology, polarisation properties and sub-mm variability in
perspective with a relatively modest commitment of time that would be
impossible with current instrumentation. We also consider the role that could
be played by other continuum wavelengths, heterodyne instruments or other
facilities in contributing towards these objectives.

arXiv

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Other Link： http://arxiv.org/pdf/2002.03100v1

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

We present the highest resolution single-dish submillimetre observations of
the detached shell source U Antliae to date. The observations were obtained at
$450~\micron$ and $850~\micron$ with SCUBA-2 instrument on the James Clerk
Maxwell Telescope as part of the Nearby Evolved Stars Survey. The emission at
$850~\micron$ peaks at $40\arcsec$ with hints of a second peak seen at $\sim
20\arcsec$. The emission can be traced out to a radius of $56\arcsec$ at a
$3\sigma$ level. The outer peak observed at $850~\micron$ aligns well with the
peak observed at Herschel/PACS wavelengths. With the help of spectral energy
distribution fitting and radiative transfer calculations of multiple-shell
models for the circumstellar envelope, we explore the various shell structures
and the variation of grain sizes along the in the circumstellar envelope. We
determine a total shell dust mass of $(2.0 \pm 0.3) \times 10^{-5}$ M$_{\odot}$
and established that the thermal pulse which gave rise to the detached shell
occurred 3500 $\pm$ 500 years ago.

DOI： 10.1093/mnras/stz2334

arXiv

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Other Link： http://arxiv.org/pdf/1908.04575v1

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

We present the POL-2 850 $\mu$m linear polarization map of the Barnard 1
clump in the Perseus molecular cloud complex from the B-fields In STar-forming
Region Observations (BISTRO) survey at the James Clerk Maxwell Telescope. We
find a trend of decreasing polarization fraction as a function of total
intensity, which we link to depolarization effects towards higher density
regions of the cloud. We then use the polarization data at 850 $\mu$m to infer
the plane-of-sky orientation of the large-scale magnetic field in Barnard 1.
This magnetic field runs North-South across most of the cloud, with the
exception of B1-c where it turns more East-West. From the dispersion of
polarization angles, we calculate a turbulence correlation length of $5.0 \pm
2.5$ arcsec ($1500$ au), and a turbulent-to-total magnetic energy ratio of $0.5
\pm 0.3$ inside the cloud. We combine this turbulent-to-total magnetic energy
ratio with observations of NH$_3$ molecular lines from the Green Bank Ammonia
Survey (GAS) to estimate the strength of the plane-of-sky component of the
magnetic field through the Davis-Chandrasekhar-Fermi method. With a
plane-of-sky amplitude of $120 \pm 60$ $\mu$G and a criticality criterion
$\lambda_c = 3.0 \pm 1.5$, we find that Barnard 1 is a supercritical molecular
cloud with a magnetic field nearly dominated by its turbulent component.

DOI： 10.3847/1538-4357/ab1b23

arXiv

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Other Link： http://arxiv.org/pdf/1904.07221v2

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

We report 850~$\mu$m dust polarization observations of a low-mass ($\sim$12
$M_{\odot}$) starless core in the $\rho$ Ophiuchus cloud, Ophiuchus C, made
with the POL-2 instrument on the James Clerk Maxwell Telescope (JCMT) as part
of the JCMT B-fields In STar-forming Region Observations (BISTRO) survey. We
detect an ordered magnetic field projected on the plane of sky in the starless
core. The magnetic field across the $\sim$0.1~pc core shows a predominant
northeast-southwest orientation centering between $\sim$40$^\circ$ to
$\sim$100$^\circ$, indicating that the field in the core is well aligned with
the magnetic field in lower-density regions of the cloud probed by
near-infrared observations and also the cloud-scale magnetic field traced by
Planck observations. The polarization percentage ($P$) decreases with an
increasing total intensity ($I$) with a power-law index of $-$1.03 $\pm$ 0.05.
We estimate the plane-of-sky field strength ($B_{\mathrm{pos } }$) using modified
Davis-Chandrasekhar-Fermi (DCF) methods based on structure function (SF),
auto-correlation (ACF), and unsharp masking (UM) analyses. We find that the
estimates from the SF, ACF, and UM methods yield strengths of 103 $\pm$ 46
$\mu$G, 136 $\pm$ 69 $\mu$G, and 213 $\pm$ 115 $\mu$G, respectively. Our
calculations suggest that the Ophiuchus C core is near magnetically critical or
slightly magnetically supercritical (i.e. unstable to collapse). The total
magnetic energy calculated from the SF method is comparable to the turbulent
energy in Ophiuchus C, while the ACF method and the UM method only set upper
limits for the total magnetic energy because of large uncertainties.

DOI： 10.3847/1538-4357/ab0958

arXiv

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Other Link： http://arxiv.org/pdf/1902.07734v1

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

To shed light on the early phase of a low-mass protostar formation process,
we conducted interferometric observations towards a protostar GF9-2 using the
CARMA and SMA. The observations have been carried out in the CO J=3-2 line and
in the continuum emission at the wavelengths of 3 mm, 1 mm and 850 micron. All
the continuum images detected a single point-like source with a radius of
250+/-80 AU at the center of the previously known ~3 Msun molecular cloud core.
A compact emission is detected towards the object at the Spitzer MIPS and IRAC
bands as well as the four bands at the WISE. Our spectroscopic imaging of the
CO line revealed that the continuum source is driving a 1000 AU scale molecular
outflow, including a pair of lobes where a collimated "higher" velocity red
lobe exists inside a poorly collimated "lower" velocity red lobe. These lobes
are rather young and the least powerful ones so far detected. A protostellar
mass of M~<0.06 Msun was estimated using an upper limit of the protostellar age
of (4+/-1)x10^3 yrs and an inferred non-spherical steady mass accretion rate of
~10^{-5} Msun/yr. Together with results from an SED analysis, we discuss that
the outflow system is driven by a protostar whose surface temperature
of~3,000K, and that the natal cloud core is being dispersed by the outflow.

DOI： 10.3847/1538-4357/aaf85c

arXiv

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Other Link： http://arxiv.org/pdf/1812.07806v1

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

We present the 850 $\mu$m polarization observations toward the IC5146
filamentary cloud taken using the Submillimetre Common-User Bolometer Array 2
(SCUBA-2) and its associated polarimeter (POL-2), mounted on the James Clerk
Maxwell Telescope (JCMT), as part of the B-fields In STar forming Regions
Observations (BISTRO). This work is aimed at revealing the magnetic field
morphology within a core-scale ($\lesssim 1.0$ pc) hub-filament structure (HFS)
located at the end of a parsec-scale filament. To investigate whether or not
the observed polarization traces the magnetic field in the HFS, we analyze the
dependence between the observed polarization fraction and total intensity using
a Bayesian approach with the polarization fraction described by the Rice
likelihood function, which can correctly describe the probability density
function (PDF) of the observed polarization fraction for low signal-to-noise
ratio (SNR) data. We find a power-law dependence between the polarization
fraction and total intensity with an index of 0.56 in $A_V\sim$ 20--300 mag
regions, suggesting that the dust grains in these dense regions can still be
aligned with magnetic fields in the IC5146 regions. Our polarization maps
reveal a curved magnetic field, possibly dragged by the contraction along the
parsec-scale filament. We further obtain a magnetic field strength of
0.5$\pm$0.2 mG toward the central hub using the Davis-Chandrasekhar-Fermi
method, corresponding to a mass-to-flux criticality of $\sim$ $1.3\pm0.4$ and
an Alfv\'{e}nic Mach number of $<$0.6. These results suggest that gravity and
magnetic field is currently of comparable importance in the HFS, and turbulence
is less important.

DOI： 10.3847/1538-4357/ab13a2

Scopus

arXiv

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Other Link： http://arxiv.org/pdf/1812.05818v3

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

We present the results of dust emission polarization measurements of
Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer
Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James
Clerk Maxwell Telescope (JCMT) in Hawaii. This work is part of the B-fields In
Star-forming Region Observations (BISTRO) survey initiated to understand the
role of magnetic fields in star formation for nearby star-forming molecular
clouds. We present a first look at the geometry and strength of magnetic fields
in Oph-B. The field geometry is traced over $\sim$0.2 pc, with clear detection
of both of the sub-clumps of Oph-B. The field pattern appears significantly
disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered,
with a tendency to be along the major axis of the clump, parallel to the
filamentary structure within which it lies. The degree of polarization
decreases systematically towards the dense core material in the two sub-clumps.
The field lines in the lower density material along the periphery are smoothly
joined to the large scale magnetic fields probed by NIR polarization
observations. We estimated a magnetic field strength of 630$\pm$410 $\mu$G in
the Oph-B2 sub-clump using a Davis-Chandeasekhar-Fermi analysis. With this
magnetic field strength, we find a mass-to-flux ratio $\lambda$= 1.6$\pm$1.1,
which suggests that the Oph-B2 clump is slightly magnetically supercritical.

DOI： 10.3847/1538-4357/aac4a6

arXiv

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Other Link： http://arxiv.org/pdf/1805.06131v2

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

We present 850 $\mu$m imaging polarimetry data of the $\rho$ Oph-A core taken
with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its
polarimeter (POL-2), as part of our ongoing survey project, BISTRO (B-fields In
STar forming RegiOns). The polarization vectors are used to identify the
orientation of the magnetic field projected on the plane of the sky at a
resolution of 0.01 pc. We identify 10 subregions with distinct polarization
fractions and angles in the 0.2 pc $\rho$ Oph A core; some of them can be part
of a coherent magnetic field structure in the $\rho$ Oph region. The results
are consistent with previous observations of the brightest regions of $\rho$
Oph-A, where the degrees of polarization are at a level of a few percents, but
our data reveal for the first time the magnetic field structures in the fainter
regions surrounding the core where the degree of polarization is much higher
($> 5 \%$). A comparison with previous near-infrared polarimetric data shows
that there are several magnetic field components which are consistent at
near-infrared and submillimeter wavelengths. Using the
Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in
several sub-core regions, which range from approximately 0.2 to 5 mG. We also
find a correlation between the magnetic field orientations projected on the sky
with the core centroid velocity components.

DOI： 10.3847/1538-4357/aabd82

Web of Science

arXiv

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Other Link： http://arxiv.org/pdf/1804.09313v1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

Evolved stars experience high mass-loss rates forming thick circumstellar envelopes (CSEs). The circumstellar material is made of the result of stellar nucleosynthesis and, as such, plays a crucial role in the chemical evolution of galaxies and the universe. Since asymmetric geometries of CSEs are common, and with very complex structures for some cases, radiative pressure from the stars can explain only a small portion of the massloss processes
thus the essential driving mechanism is still unknown, particularly for high-mass stars. Here we report on magnetic field measurements associated with the well-known extreme red supergiant (RSG) VY Canis Majoris (VY CMa). We measured the linear polarization and the Zeeman splitting of the SiO v = 0, J = 1-0 transition using a sensitive radio interferometer. The measured magnetic field strengths are surprisingly high
their upper limits range between 150 and 650 G within 530 au (~80 R∗) of the star. The lower limit of the field strength is expected to be at least ~10 G based on the high degree of linear polarization. Since the field strengths are very high, the magnetic field must be a key element in understanding the stellar evolution of VY CMa, as well as the dynamical and chemical evolution of the complex CSE of the star. M-type RSGs, with large stellar surface, were thought to be very slow rotators. This would seem to make a dynamo in operation difficult, and would also dilute any fossil magnetic field. At least for VY CMa, we expect that powerful dynamo processes must still be active to generate the intense magnetic field.

DOI： 10.1093/pasj/psx110

Scopus

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

The Survey of Water and Ammonia in the Galactic Center (SWAG) covers the
Central Molecular Zone (CMZ) of the Milky Way at frequencies between 21.2 and
25.4 GHz obtained at the Australia Telescope Compact Array at $\sim 0.9$ pc
spatial and $\sim 2.0$ km s$^{-1}$ spectral resolution. In this paper, we
present data on the inner $\sim 250$ pc ($1.4^\circ$) between Sgr C and Sgr B2.
We focus on the hyperfine structure of the metastable ammonia inversion lines
(J,K) = (1,1) - (6,6) to derive column density, kinematics, opacity and kinetic
gas temperature. In the CMZ molecular clouds, we find typical line widths of
$8-16$ km s$^{-1}$ and extended regions of optically thick ($\tau > 1$)
emission. Two components in kinetic temperature are detected at $25-50$ K and
$60-100$ K, both being significantly hotter than dust temperatures throughout
the CMZ. We discuss the physical state of the CMZ gas as traced by ammonia in
the context of the orbital model by Kruijssen et al. (2015) that interprets the
observed distribution as a stream of molecular clouds following an open
eccentric orbit. This allows us to statistically investigate the time
dependencies of gas temperature, column density and line width. We find heating
rates between $\sim 50$ and $\sim 100$ K Myr$^{-1}$ along the stream orbit. No
strong signs of time dependence are found for column density or line width.
These quantities are likely dominated by cloud-to-cloud variations. Our results
qualitatively match the predictions of the current model of tidal triggering of
cloud collapse, orbital kinematics and the observation of an evolutionary
sequence of increasing star formation activity with orbital phase.

DOI： 10.3847/1538-4357/aa951c

arXiv

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Other Link： http://arxiv.org/pdf/1710.06902v1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m
telescope (FUGIN) project is one of the legacy projects using the new
multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This
project aims to investigate the distribution, kinematics, and physical
properties of both diffuse and dense molecular gas in the Galaxy at once by
observing 12CO, 13CO, and C18O J=1-0 lines simultaneously. The mapping regions
are a part of the 1st quadrant (10d < l < 50d, |b| < 1d) and the 3rd quadrant
(198d < l <236d, |b| < 1d) of the Galaxy, where spiral arms, bar structure, and
the molecular gas ring are included. This survey achieves the highest angular
resolution to date (~20") for the Galactic plane survey in the CO J=1-0 lines,
which makes it possible to find dense clumps located farther away than the
previous surveys. FUGIN will provide us with an invaluable dataset for
investigating the physics of the galactic interstellar medium (ISM),
particularly the evolution of interstellar gas covering galactic scale
structures to the internal structures of giant molecular clouds, such as small
filament/clump/core. We present an overview of the FUGIN project, observation
plan, and initial results, which reveal wide-field and detailed structures of
molecular clouds, such as entangled filaments that have not been obvious in
previous surveys, and large-scale kinematics of molecular gas such as spiral
arms.

DOI： 10.1093/pasj/psx061

arXiv

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Other Link： http://arxiv.org/pdf/1707.05981v1

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

We determine the magnetic field strength in the OMC 1 region of the Orion A
filament via a new implementation of the Chandrasekhar-Fermi method using
observations performed as part of the James Clerk Maxwell Telescope (JCMT)
B-Fields In Star-Forming Region Observations (BISTRO) survey with the POL-2
instrument. We combine BISTRO data with archival SCUBA-2 and HARP observations
to find a plane-of-sky magnetic field strength in OMC 1 of $B_{\rm
pos}=6.6\pm4.7$ mG, where $\delta B_{\rm pos}=4.7$ mG represents a
predominantly systematic uncertainty. We develop a new method for measuring
angular dispersion, analogous to unsharp masking. We find a magnetic energy
density of $\sim1.7\times 10^{-7}$ Jm$^{-3}$ in OMC 1, comparable both to the
gravitational potential energy density of OMC 1 ($\sim 10^{-7}$ Jm$^{-3}$), and
to the energy density in the Orion BN/KL outflow ($\sim 10^{-7}$ Jm$^{-3}$). We
find that neither the Alfv\'{e}n velocity in OMC 1 nor the velocity of the
super-Alfv\'{e}nic outflow ejecta is sufficiently large for the BN/KL outflow
to have caused large-scale distortion of the local magnetic field in the
$\sim$500-year lifetime of the outflow. Hence, we propose that the hour-glass
field morphology in OMC 1 is caused by the distortion of a primordial
cylindrically-symmetric magnetic field by the gravitational fragmentation of
the filament and/or the gravitational interaction of the BN/KL and S clumps. We
find that OMC 1 is currently in or near magnetically-supported equilibrium, and
that the current large-scale morphology of the BN/KL outflow is regulated by
the geometry of the magnetic field in OMC 1, and not vice versa.

DOI： 10.3847/1538-4357/aa80e5

arXiv

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Other Link： http://arxiv.org/pdf/1707.05269v1

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

We present the first results from the B-fields In STar-forming Region
Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer
Array 2 (SCUBA-2) camera, with its associated polarimeter (POL-2), on the James
Clerk Maxwell Telescope (JCMT) in Hawaii. We discuss the survey's aims and
objectives. We describe the rationale behind the survey, and the questions
which the survey will aim to answer. The most important of these is the role of
magnetic fields in the star formation process on the scale of individual
filaments and cores in dense regions. We describe the data acquisition and
reduction processes for POL-2, demonstrating both repeatability and consistency
with previous data. We present a first-look analysis of the first results from
the BISTRO survey in the OMC 1 region. We see that the magnetic field lies
approximately perpendicular to the famous 'integral filament' in the densest
regions of that filament. Furthermore, we see an 'hour-glass' magnetic field
morphology extending beyond the densest region of the integral filament into
the less-dense surrounding material, and discuss possible causes for this. We
also discuss the more complex morphology seen along the Orion Bar region. We
examine the morphology of the field along the lower-density north-eastern
filament. We find consistency with previous theoretical models that predict
magnetic fields lying parallel to low-density, non-self-gravitating filaments,
and perpendicular to higher-density, self-gravitating filaments.

DOI： 10.3847/1538-4357/aa70a0

Scopus

arXiv

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Other Link： http://arxiv.org/pdf/1704.08552v1

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

We observed thirteen Planck cold clumps with the James Clerk Maxwell
Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N$_2$H$^+$
distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2
dust distribution. The 82 GHz HC$_3$N, 82 GHz CCS, and 94 GHz CCS emission are
often distributed differently with respect to the N$_2$H$^+$ emission. The CCS
emission, which is known to be abundant in starless molecular cloud cores, is
often very clumpy in the observed targets. We made deep single-pointing
observations in DNC, HN$^{13}$C, N$_2$D$^+$, cyclic-C$_3$H$_2$ toward nine
clumps. The detection rate of N$_2$D$^+$ is 50\%. Furthermore, we observed the
NH$_3$ emission toward 15 Planck cold clumps to estimate the kinetic
temperature, and confirmed that most of targets are cold ($\lesssim$ 20 K). In
two of the starless clumps observe, the CCS emission is distributed as it
surrounds the N$_2$H$^+$ core (chemically evolved gas), which resembles the
case of L1544, a prestellar core showing collapse. In addition, we detected
both DNC and N$_2$D$^+$. These two clumps are most likely on the verge of star
formation. We introduce the Chemical Evolution Factor (CEF) for starless cores
to describe the chemical evolutionary stage, and analyze the observed Planck
cold clumps.

DOI： 10.3847/1538-4365/228/2/12

arXiv

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Other Link： http://arxiv.org/pdf/1612.00488v1

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

We developed a dual-linear-polarization HEMT (High Electron Mobility
Transistor) amplifier receiver system of the 45-GHz band (hereafter Z45), and
installed it in the Nobeyama 45-m radio telescope. The receiver system is
designed to conduct polarization observations by taking the cross correlation
of two linearly-polarized components, from which we process full-Stokes
spectroscopy. We aim to measure the magnetic field strength through the Zeeman
effect of the emission line of CCS ($J_N=4_3-3_2$) toward pre-protostellar
cores. A linear-polarization receiver system has a smaller contribution of
instrumental polarization components to the Stokes $V$ spectra than that of the
circular polarization system, so that it is easier to obtain the Stokes $V$
spectra. The receiver has an RF frequency of 42 $-$ 46 GHz and an intermediate
frequency (IF) band of 4$-$8 GHz. The typical noise temperature is about 50 K,
and the system noise temperature ranges from 100 K to 150K over the frequency
of 42 $-$ 46 GHz. The receiver system is connected to two spectrometers, SAM45
and PolariS. SAM45 is a highly flexible FX-type digital spectrometer with a
finest frequency resolution of 3.81 kHz. PolariS is a newly-developed digital
spectrometer with a finest frequency resolution of 60 Hz, having a capability
to process the full-Stokes spectroscopy. The Half Power Beam Width (HPBW) of
the beam was measured to be 37$"$ at 43 GHz. The main beam efficiency of the
Gaussian main beam was derived to be 0.72 at 43 GHz. The SiO maser observations
show that the beam pattern is reasonably round at about 10 \% of the peak
intensity and the side-lobe level was less than 3 \% of the peak intensity.
Finally, we present some examples of astronomical observations using Z45.

DOI： 10.1093/pasj/psv088

arXiv

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Other Link： http://arxiv.org/pdf/1509.02631v1

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

To study physical properties of the natal filament gas around the cloud core
harboring an exceptionally young low-mass protostar GF9-2, we carried out J=1-0
line observations of 12CO, 13CO, and C18O molecules using the Nobeyama 45m
telescope. The mapping area covers ~1/5 of the whole filament. Our 13CO and
C18O maps clearly demonstrate that the core formed at the local density maxima
of the filament, and the internal motions of the filament gas are totally
governed by turbulence with Mach number of ~2. We estimated the scale height of
the filament to be H = 0.3 ~ 0.7 pc, yielding the central density of n_c = 700
~4200 cm^-3. Our analysis adopting an isothermal cylinder model shows that the
filament is supported by the turbulent and magnetic pressures against the
radial and axial collapse due to self-gravity. Since both the dissipation time
scales of the turbulence and the transverse magnetic fields can be comparable
to the free-fall time of the filament gas of 10^6 years, we conclude that the
local decay of the supersonic turbulence made the filament gas locally
unstable, hence making the core collapse. Furthermore, we newly detected a gas
condensation with velocity width enhancement to ~0.3 pc south-west of the GF9-2
core. The condensation has a radius of ~0.15 pc and an LTE mass of ~5 Msun. Its
internal motion is turbulent with Mach number of ~3, suggestive of a
gravitationally unbound state. Considering the uncertainties in our estimates,
however, we propose that the condensation is a precursor of a cloud core which
would have been produced by the collision of the two gas components identified
in the filament.

DOI： 10.1088/0004-637X/793/2/94

Scopus

arXiv

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Other Link： http://arxiv.org/pdf/1407.4857v1

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

The Serpens South infrared dark cloud consists of several filamentary ridges,
some of which fragment into dense clumps. On the basis of CCS ($J_N=4_3-3_2$),
HC$_3$N ($J=5-4$), N$_2$H$^+$ ($J=1-0$), and SiO ($J=2-1, v=0$) observations,
we investigated the kinematics and chemical evolution of these filamentary
ridges. We find that CCS is extremely abundant along the main filament in the
protocluster clump. We emphasize that Serpens South is the first
cluster-forming region where extremely-strong CCS emission is detected. The
CCS-to-N$_2$H$^+$ abundance ratio is estimated to be about 0.5 toward the
protocluster clump, whereas it is about 3 in the other parts of the main
filament. We identify six dense ridges with different $V_{\rm LSR}$. These
ridges appear to converge toward the protocluster clump, suggesting that the
collisions of these ridges may have triggered cluster formation. The collisions
presumably happened within a few $\times \ 10^5$ yr because CCS is abundant
only in such a short time. The short lifetime agrees with the fact that the
number fraction of Class I objects, whose typical lifetime is $0.4 \times \
10^5$ yr, is extremely high as about 70 percent in the protocluster clump. In
the northern part, two ridges appear to have partially collided, forming a
V-shape clump. In addition, we detected strong bipolar SiO emission that is due
to the molecular outflow blowing out of the protostellar clump, as well as
extended weak SiO emission that may originate from the filament collisions.

DOI： 10.1088/2041-8205/791/2/L23

arXiv

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Other Link： http://arxiv.org/pdf/1407.1235v1

Language：English   Publishing type：Research paper (bulletin of university, research institution)   Publisher：SPRINGER  

Preliminary results from our Submillimeter Array observations towards an exceptionally young low-mass protostar, GF 9-2, are briefly reported.

DOI： 10.1007/978-3-319-03041-8_54

Web of Science

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

We present the first detection of polarization around the Class 0 low-mass
protostar L1157-mm at two different wavelengths. We show polarimetric maps at
large scales (10" resolution at 350 um) from the SHARC-II Polarimeter and at
smaller scales (1.2"-4.5" at 1.3 mm) from the Combined Array for Research in
Millimeter-wave Astronomy (CARMA). The observations are consistent with each
other and show inferred magnetic field lines aligned with the outflow. The
CARMA observations suggest a full hourglass magnetic field morphology centered
about the core; this is only the second well-defined hourglass detected around
a low-mass protostar to date. We apply two different methods to CARMA
polarimetric observations to estimate the plane-of-sky magnetic field
magnitude, finding values of 1.4 and 3.4 mG.

DOI： 10.1088/2041-8205/769/1/L15

arXiv

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Other Link： http://arxiv.org/pdf/1304.6739v1

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

arXiv

Other Link： http://www.aanda.org/articles/aa/abs/2011/01/aa14402-10/aa14402-10.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

Aims. We carried out sub-arcsecond resolution observations towards the high-mass star formation region G19.61-0.23, in both continuum and molecular line emission. While the centimeter continuum images, representing ultra compact HII regions, will be discussed in detail in a forthcoming paper, here we focus on the (sub) mm emission, devoting special attention to the hot molecular core (HMC).
Methods. A set of multi wavelength continuum and molecular line emission data between 6 cm and 890 mu m were obtained with the Very Large Array, Nobeyama Millimeter Array, Owens Valley Radio Observatory millimeter array, and Submillimeter Array (SMA). These data were analyzed in conjunction with previously published data.
Results. Our SMA observations resolve the HMC into three cores whose masses are on the order of 10(1)-10(3) M-circle dot. No submm core exhibits detectable free-free emission in the centimeter regime, but appear to be associated with masers and thermal line emission from complex organic molecules. Towards the most massive core, SMA1, the CH3CN (18(K)-17(K)) lines provide hints of rotation about the axis of a jet/outflow traced by H2O maser and (HCO+)-C-13(1-0) line emission. Inverse P-Cygni profiles of the (CO)-C-13 (3-2) and (CO)-O-18 (3-2) lines seen towards SMA1 indicate that the central high-mass (proto) star(s) is (are) still gaining mass with an accretion rate &gt;= 3 x 10(-3) M-circle dot yr(-1). Owing to the linear scales and high accretion rate, we hypothesize that we are observing an accretion flow towards a star cluster in the making, rather than towards a single massive star.

DOI： 10.1051/0004-6361/201014402

Web of Science

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

In order to investigate when and how the birth of a protostellar core occurs,
we made survey observations of four well-studied dense cores in the Taurus
molecular cloud using CO transitions in submillimeter bands. We report here the
detection of unexpectedly warm (~ 30 - 70 K), extended (radius of ~ 2400 AU),
dense (a few times 10^{5} cm^{-3}) gas at the heart of one of the dense cores,
L1521F (MC27), within the cold dynamically collapsing components. We argue that
the detected warm, extended, dense gas may originate from shock regions caused
by collisions between the dynamically collapsing components and
outflowing/rotating components within the dense core. We propose a new stage of
star formation, "warm-in-cold core stage (WICCS)", i.e., the cold collapsing
envelope encases the warm extended dense gas at the center due to the formation
of a protostellar core. WICCS would constitutes a missing link in evolution
between a cold quiescent starless core and a young protostar in class 0 stage
that has a large-scale bipolar outflow.

DOI： 10.1088/0004-637X/706/2/L226

arXiv

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Other Link： http://arxiv.org/pdf/0910.0463v1

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

We present single-dish 350 micron dust continuum polarimetry as well as HCN
and HCO+ J=4-3 rotational emission spectra obtained on NGC 1333 IRAS 4. The
polarimetry indicates a uniform field morphology over a 20" radius from the
peak continuum flux of IRAS 4A, in agreement with models of magnetically
supported cloud collapse. The field morphology around IRAS 4B appears to be
quite distinct however, with indications of depolarization observed towards the
peak flux of this source. Inverse P-Cygni profiles are observed in the HCN
J=4-3 line spectra towards IRAS 4A, providing a clear indication of infall gas
motions. Taken together, the evidence gathered here appears to support the
scenario that IRAS 4A is a cloud core in a critical state of support against
gravitational collapse.

DOI： 10.1088/0004-637X/702/2/1584

arXiv

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Other Link： http://arxiv.org/pdf/0907.1301v1

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

We used the Extended Submillimeter Array (eSMA) in its most extended
configuration to investigate the innermost (within a radius of 290 R* from the
star) circumstellar envelope (CSE) of IRC+10216. We imaged the CSE using HCN
and other molecular lines with a beam size of 0."22 x 0."46, deeply into the
very inner edge (15 R*) of the envelope where the expansion velocity is only 3
km/s. The excitation mechanism of hot HCN and KCl maser lines is discussed. HCN
maser components are spatially resolved for the first time on an astronomical
object. We identified two discrete regions in the envelope: a region with a
radius of . 15 R*, where molecular species have just formed and the gas has
begun to be accelerated (region I) and a shell region (region II) with a radius
of 23 R* and a thickness of 15 R*, whose expansion velocity has reached up to
13 km/s, nearly the terminal velocity of 15 km/s. The Si$^{34}$S line detected
in region I shows a large expansion velocity of 16 km/s due to strong wing
components, indicating that the emission may arise from a shock region in the
innermost envelope. In region II, the P.A. of the most copious mass loss
direction was found to be 120 +/- 10 degrees, which may correspond to the
equatorial direction of the star. Region II contains a torus-like feature.
These two regions may have emerged due to significant differences in the size
distributions of the dust particles in the two regions.

DOI： 10.1088/0004-637X/698/2/1924

DOI： 10.1088/0004-637X/727/1/60

arXiv

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Other Link： http://arxiv.org/pdf/0904.0280v1

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

Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the field of extragalactic astrophysics.
Community-based White Paper to Astro2010 in response to the call for such
papers.

arXiv

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Other Link： http://arxiv.org/pdf/0902.4224v1

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

Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the field of cosmology. Community-based
White Paper to Astro2010 in response to the call for such papers.

arXiv

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Other Link： http://arxiv.org/pdf/0902.4226v1

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

Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the fields of stars and stellar
evolution. Community-based White Paper to Astro2010 in response to the call for
such papers.

arXiv

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Other Link： http://arxiv.org/pdf/0902.4222v1

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

Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the fields of planetary systems and star
formation. Community-based White Paper to Astro2010 in response to the call for
such papers.

arXiv

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Other Link： http://arxiv.org/pdf/0902.4220v1

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

Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the field of Galactic science.
Community-based White Paper to Astro2010 in response to the call for such
papers.

arXiv

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Other Link： http://arxiv.org/pdf/0902.4217v1

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

We present spectroscopic evidence for infall motion of gas in the natal cloud
core harboring an extremely young low-mass protostar GF9-2. We previously
discussed that the ongoing collapse of the GF9-2 core has agreement with the
Larson-Penston-Hunter (LPH) theoretical solution for the gravitational collapse
of a core (Furuya et al.; paper I). To discuss the gas infall on firmer ground,
we have carried out On-The-Fly mapping observations of the HCO+ (1--0) line
using the Nobeyama 45m telescope equipped with the 25 Beam Array Receiver
System. Furthermore, we observed the HCN (1--0) line with the 45m telescope,
and the HCO+ (3--2) line with the Caltech Submillimeter Observatory 10.4 m
telescope. The optically thick HCO+ and HCN lines show blueskewed profiles
whose deepest absorptions are seen at the peak velocity of optically thin
lines, i.e., the systemic velocity of the cloud (paper I), indicating the
presence of gas infall toward the central protostar. We compared the observed
HCO+ line profiles with model ones by solving the radiative transfer in the
core under LTE assumption.We found that the core gas has a constant infall
velocity of ~0.5 km/s in the central region, leading to a mass accretion rate
of 2.5x10^{-5} Msun/yr. Consequently, we confirm that the gas infall in the
GF9-2 core is consistent with the LPH solution.

DOI： 10.1088/0004-637X/692/2/L96

arXiv

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Other Link： http://arxiv.org/pdf/0901.0730v1

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

arXiv

Other Link： http://iopscience.iop.org/article/10.1088/0004-637X/705/1/717/meta

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

arXiv

Other Link： http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009ApJ...692L..96F&link_type=EJOURNAL&db_key=AST&high=

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

We report the first science observations and results obtained with the
"extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT
(James Clerk Maxwell Telescope) and CSO (Caltech Submillimeter Observatory).
Redshifted absorptions at z=0.886 of CI (^3P_1 - ^3P_0) were observed with the
eSMA with an angular resolution of 0.55"x0.22" at 1.1 mm toward the
southwestern image of the remarkable lensed quasar PKS 1830-211, but not toward
the northeastern component at a separation of ~1". Additionally, SMA
observations of CO, 13CO and C18O (all J=4-3) were obtained toward this object:
CO was also detected toward the SW component, but none of the isotopologues
were. This is the first time [CI] is detected in this object, allowing the
first direct determination of relative abundances of neutral atomic carbon to
CO in the molecular clouds of a spiral galaxy at z>0.1. The [CI] and CO
profiles can be decomposed into two and three velocity components respectively.
We derive C/CO column density ratios ranging from <0.5 (representative of dense
cores) to ~2.5 (close to translucent clouds values). This could indicate that
we are seeing environments with different physical conditions or that we are
witnessing chemical evolution of regions where C has not completely been
converted into CO.

DOI： 10.1088/0004-637X/690/2/L130

arXiv

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Other Link： http://arxiv.org/pdf/0811.3944v1

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

The eSMA ("extended SMA") combines the SMA, JCMT and CSO into a single
facility, providing enhanced sensitivity and spatial resolution owing to the
increased collecting area at the longest baselines. Until ALMA early science
observing (2011), the eSMA will be the facility capable of the highest angular
resolution observations at 345 GHz. The gain in sensitivity and resolution will
bring new insights in a variety of fields, such as protoplanetary/transition
disks, high-mass star formation, solar system bodies, nearby and high-z
galaxies. Therefore the eSMA is an important facility to prepare the grounds
for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been
substantial progress toward making the eSMA into a working interferometer. In
particular, (i) new 345-GHz receivers, that match the capabilities of the SMA
system, were installed at the JCMT and CSO; (ii) numerous tests have been
performed for receiver, correlator and baseline calibrations in order to
determine and take into account the effects arising from the differences
between the three types of antennas; (iii) first fringes at 345 GHz were
obtained on August 30 2007, and the array has entered the science-verification
stage.
We report on the characteristics of the eSMA and its measured performance at
230 GHz and that expected at 345 GHz. We also present the results of the
commissioning and some initial science-verification observations, including the
first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located
along the line of sight to the lensed quasar PKS1830-211, and on the imaging of
the vibrationally excited HCN line towards IRC+10216.

DOI： 10.1117/12.788949

arXiv

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Other Link： http://arxiv.org/pdf/0808.2554v1

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

We carried out an unbiased mapping survey of dense molecular cloud cores
traced by the NH3 (1,1) and (2,2) inversion lines in the GF9 filament which
contains an extremely young low-mass protostar GF9-2 (Furuya et al. 2006, ApJ,
653, 1369). The survey was conducted using the Nobeyama 45m telescope over a
region of ~1.5 deg with an angular resolution of 73". The large-scale map
revealed that the filament contains at least 7 dense cores, as well as 3
possible ones, located at regular intervals of ~0.9 pc. Our analysis shows that
these cores have kinetic temperatures of $\lesssim$ 10 K and LTE-masses of 1.8
-- 8.2 Msun, making them typical sites of low-mass star formation. All the
identified cores are likely to be gravitationally unstable because their
LTE-masses are larger than their virial masses. Since the LTE-masses and
separations of the cores are consistent with the Jeans masses and lengths,
respectively, for the low-density ambient gas, we argue that the identified
cores have formed via the gravitational fragmentation of the natal filamentary
cloud.

DOI： 10.1093/pasj/60.3.421

arXiv

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Other Link： http://arxiv.org/pdf/0805.0021v1

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

We used the Submillimeter Array to map the angular distribution of the
H30$\alpha$ recombination line (231.9 GHz) in the circumstellar region of the
peculiar star MWC349A. The resolution was $1\farcs2$, but because of high
signal-to-noise ratio we measured the positions of all maser components to
accuracies better than $0\farcs01$, at a velocity resolution of $1 kms$. The
two strongest maser components (called high velocity components) at velocities
near -14 and $32 kms$ are separated by $0\farcs048 \pm 0\farcs001$ (60 AU)
along a position angle of $102 \pm 1\arcdeg$. The distribution of maser
emission at velocities between and beyond these two strongest components were
also provided. The continuum emission lies at the center of the maser
distribution to within 10 mas. The masers appear to trace a nearly edge-on
rotating disk structure, reminiscent of the water masers in Keplerian rotation
in the nuclear accretion disk of the galaxy NGC4258. However, the maser
components in MWC349A do not follow a simple Keplerian kinematic prescription
with $v \sim r^{-1/2}$, but have a larger power law index. We explore the
possibility that the high velocity masers trace spiral density or shock waves.
We also emphasize caution in the interpretation of relative centroid maser
positions where the maser is not clearly resolved in position or velocity, and
we present simulations that illustrate the range of applicability of the
centroiding method.

DOI： 10.1086/529132

arXiv

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Other Link： http://arxiv.org/pdf/0801.0608v1

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

We present a study of the natal core harboring the class 0 protostar GF9-2 in
the filamentary dark cloud GF 9 (d = 200 pc). GF9-2 stands unique in the sense
that it shows H2O maser emission, a clear signpost of protostar formation,
whereas it does not have a high-velocity large-scale molecular outflow
evidenced by our deep search for CO wing emission. These facts indicate that
GF9-2 core is early enough after star formation so that it still retains some
information of initial conditions for collapse. Our 350 um dust continuum
emission image revealed the presence of a protostellar envelope in the center
of a molecular core. The mass of the envelope is ~0.6 Msun from the 350 um flux
density, while LTE mass of the core is ~3 Msun from moleuclar line
observations. Combining visibility data from the OVRO mm-array and the 45m
telescope, we found that the core has a radial density profile of
$\rho(r)\propto r^{-2}$ for 0.003 < r/pc < 0.08 region. Molecular line data
analysis revealed that the velocity width of the core gas increases
inward,while the outermost region maintains a velocity dispersion of a few
times of the ambient sound speed. The broadened velocity width can be
interpreted as infall. Thus, the collapse in GF9-2 is likely to be described by
an extension of the Larson-Penston solution for the period after formation of a
central star. We derived the current mass accretion rate of ~3E-05 Msun/year
from infall velocity of ~ 0.3 km/s at r~ 7000 AU. All results suggest that
GF9-2 core has been undergoing gravitational collapse for ~ 5000 years since
the formation of central protostar(s), and that the unstable state initiated
the collapse ~2E+05 years (the free-fall time) ago.

DOI： 10.1086/508405

arXiv

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Other Link： http://arxiv.org/pdf/astro-ph/0608357v1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact (UC) H II regions toward the high-mass star-forming region G19.61-0.23. In addition, we performed 1.2 mm imaging with SIMBA and retrieved 3.5 and 2 cm images from the VLA archive database. The newly obtained 3 mm image brings information on a cluster of high-mass ( proto) stars located in the innermost and densest part of the parsec-scale clump detected in the 1.2 mm continuum. We identify a total of 10 high-mass young stellar objects: one hot core (HC) and nine UC H II regions, whose physical parameters are obtained from model fits to their continuum spectra. The ratio between the current and expected final radii of the UCH II regions ranges from 0.3 to 0.9, which leaves the possibility that all O-B stars formed simultaneously. Under the opposite assumption, namely, that star formation occurred randomly, we estimate that the HC lifetime is less than &SIM; 1/3 of that of UC H II regions on the basis of the source number ratio between them.

DOI： 10.1086/429286

Web of Science

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

Using the partially completed Submillimeter Array with five antennas, we have
observed the CO J=2-1 and 3-2 emission from the envelope surrounding the carbon
star V Hya. The high-angular resolution (2"-4") maps show that V Hya is
powering a bipolar molecular jet having an extreme velocity of 70-185 km/s. The
axis of this high velocity jet is perpendicular to the major axis of the
flattened disk-like envelope, which is expanding with a velocity of ~16
km/s.There is a third kinematic component, a medium-velocity wind having a
deprojected velocity of 40-120 km/s moving along the disk plane. Both the high
velocity jet and the medium velocity wind have a dynamical time scale of a few
hundred years. The flattened structure and the collimated jet observed in V Hya
suggests that the formation of asymmetrical structure proceeds while the
central star is still in the AGB phase

DOI： 10.1086/424382

arXiv

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Other Link： http://arxiv.org/pdf/astro-ph/0407337v1

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

DOI： 10.1093/pasj/55.6.L83

Other Link： https://arxiv.org/pdf/astro-ph/0310727.pdf

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We have designed and constructed a tunable polarimeter system to cover frequencies from 35 GHz to 250 GHz, (8.6 mm and 1.2 mm in wavelength) for the 45m telescope at Nobeyama Radio Observatory (NRO). Both circular and linear polarizations can be measured by the polarimeter. The performance of the polarimeter in astronomical observations was tested by simultaneously measuring the linear polarization of the J = 2 - 1 transition of SiO in the nu=0 and 1 states at 86 GHz toward VY CMa. The design, construction, and tests are presented briefly.

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASTRONOMICAL SOC PACIFIC  

We briefly report the results of polarimetric observations of SiO emission from late-type stars taken with a millimeter polarimeter installed at the Nobeyama 45m telescope. We found that the SiO J = 2 - 1 emission in the v = 0 state from R Cas contains a highly linearly polarized component, followed by the detection of highly linearly polarized emission of the same transition from VY CMa (Shinnaga et al. 1999). The high polarization degree is a strong evidence that the v=0 emission originates from maser action. We found out that, not only a peculiar supergiant star, but also a Mira variable star is associated with the SiO v = 0 maser.

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