Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ae10bb

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Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/addf4b

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Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/adf49c

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Publishing type：Research paper (scientific journal)  

DOI： 10.1126/sciadv.adw4512

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Publishing type：Research paper (scientific journal)  

Context. There is increasing evidence of a physical link between high-mass star formation and hub-filament systems (HFSs). However, a lack of multi-scale observations of HFS clouds hinders our understanding of the detailed and scale-dependent cloud fragmentation and associated dynamical high-mass star formation. Aims. This study aims to understand the multi-scale scenario of cloud fragmentation and associated high-mass star formation in an HFS cloud. Methods. As part of the ALMA-INFANT survey, we used 1.3 mm mosaic observations of the high-mass star-forming HFS cloud I18308 at a spatial resolution of ~3000 AU, which provided multiscale information on the HFS. We analyzed the filament and hub fragmentation properties (e.g., core separation and mass). Results. The I18308 cloud exhibits a well-defined HFS morphology in ALMA 1.3 mm continuum with two filaments (F1 and F2) converging toward the central hub. Eighteen compact cores are identified: nine in the hub, six in F1, and three in F2. Most cores are gravitationally bound and have high-mass surface densities of >1 g cm^-2, indicating their potential for high-mass star formation, especially in the hub, which already hosts an embedded UCH II region. The scale-dependent fragmentation is characterized by a cylindrical mode for F1 and F2, and a nearly-spherical Jeans-like mode for the central clumpy hub. This could be attributed to the (an)isotropic evolution of larger scale density structures into smaller scale ones. Additionally, the scale-dependent fragmentation mechanisms are identified as turbulence-driven within the filaments and gravity-driven inside the central hub. No candidate high-mass prestellar cores (>30 M_⊙) are observed across the whole cloud. In the hub, protostellar cores have higher average mass, surface density, and temperature; and smaller radius than prestellar cores, which is consistent with continuous mass accumulation during evolution. Conclusions. The well-defined HFS morphology, the absence of high-mass prestellar cores, and the increasing core mass and surface density with evolutionary stage collectively suggest a multi-scale dynamical scenario of mass accumulation for high-mass star formation in I18308....

DOI： 10.1051/0004-6361/202554634

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Publishing type：Research paper (scientific journal)  

We present the first detection of spatially resolved protostellar outflows and jets in the outer Galaxy. We observed five star-forming regions in the outer Galaxy (Sh 2-283 and NOMF05-16/19/23/63; galactocentric distance = 15.7–17.4 kpc) with the Atacama Large Millimeter/submillimeter Array. Toward Sh 2-283, we have detected distinct outflow (∼5–50 km s^‑1) and jet components (∼50–100 km s^‑1) associated with the protostar in CO(3–2) emission. The outflows and jets are well collimated, with the jets exhibiting multiple bullet structures. The position–velocity diagram along the CO flow axis shows two characteristic structures: (a) the flow velocity, which linearly increases with the position offset from the core center (the Hubble-like flow); and (b) the continuous velocity components of the periodical flows (spine-like structures), which may indicate episodic mass ejection events. The time intervals of the mass ejection events are estimated to be 900–4000 yr, based on the slopes of these spine-like structures. These characteristics align with those of nearby protostellar systems, indicating that early star formation in low-metallicity environments, such as the outer Galaxy, resembles that in the inner Galaxy. In contrast to the physical similarities, the N(SiO)/N(CO) ratio in the jet bullet appears to be lower than that measured in the low-mass protostellar sources in the inner Galaxy. This may indicate a different shock chemistry or different dust composition in the outer Galaxy source, although non–local thermodynamic equilibrium effects could also affect the observed low N(SiO)/N(CO) ratio. We also report the new detection of four other outflow sources in the outer Galaxy....

DOI： 10.3847/1538-4357/ade235

arXiv

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Publishing type：Research paper (scientific journal)  

We present ∼8–40 μm SOFIA-FORCAST images of seven regions of "clustered" star formation as part of the SOFIA Massive Star Formation Survey. We identify a total of 34 protostar candidates and build their spectral energy distributions (SEDs). We fit these SEDs with a grid of radiative transfer models based on the turbulent core accretion (TCA) theory to derive key protostellar properties, including initial core mass, M_c, clump environment mass surface density, Σ_cl, and current protostellar mass, m_*. We also carry out empirical graybody (GB) estimation of Σ_cl, which allows a case of restricted SED fitting within the TCA model grid. We also release version 2.0 of the open-source Python package sedcreator, which is designed to automate the aperture photometry and SED building and fitting process for sources in clustered environments, where flux contamination from close neighbors typically complicates the process. Using these updated methods, SED fitting yields values of M_c ∼ 30–200 M_⊙, Σ_cl,SED ∼ 0.1–3 g cm^‑2, and m_* ∼ 4–50 M_⊙. The GB fitting yields smaller values of Σ_cl,GB ≲ 1 g cm^‑2. From these results, we do not find evidence for a critical Σ_cl needed to form massive (≳8 M_⊙) stars. However, we do find tentative evidence for a dearth of the most massive (m_* ≳ 30 M_⊙) protostars in the clustered regions, suggesting a potential impact of environment on the stellar initial mass function....

DOI： 10.3847/1538-4357/adcd79

arXiv

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Publishing type：Research paper (scientific journal)  

Filamentary molecular clouds are an essential intermediate stage in the star formation process. To test whether these structures are universal throughout cosmic star formation history, it is crucial to study low-metallicity environments within the Local Group. We present an analysis of Atacama Large Millimeter/submillimeter Array (ALMA) archival data at the spatial resolution of ~0.1 pc for 17 massive young stellar objects (YSOs) in the Small Magellanic Cloud (SMC; Z ~ 0.2 Z_⊙). This sample represents approximately 30% of the YSOs confirmed by Spitzer spectroscopy. Early ALMA studies of the SMC have shown that the CO emission line traces an H₂ number density of ≳10⁴ cm^‑3, an order of magnitude higher than in typical Galactic environments. Using the CO(J = 3–2) data, we investigate the spatial and velocity distribution of molecular clouds. Our analysis shows that about 60% of the clouds have steep radial profiles from the spine of the elongated structures, while the remaining clouds have a smooth distribution and are characterized by lower brightness temperatures. We categorize the former as filaments and the latter as nonfilaments. Some of the filamentary clouds are associated with YSOs with outflows and exhibit higher temperatures, likely reflecting their formation conditions, suggesting that these clouds are younger than the nonfilamentary ones. This indicates that even if filaments form during star formation, their steep structures may become less prominent and transition to a lower-temperature state. Such transitions in structure and temperature have not been reported in metal-rich regions, highlighting a key behavior for characterizing the evolution of the interstellar medium and star formation in low-metallicity environments....

DOI： 10.3847/1538-4357/ada5f8

arXiv

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Publishing type：Research paper (scientific journal)  

Context. Evidence that the chemical characteristics around low- and high-mass protostars are similar has been found: notably, a variety of carbon-chain species and complex organic molecules (COMs) form around both types. On the other hand, the chemical compositions around intermediate-mass (IM) protostars (2 M_⊙ < m_* < 8 M_⊙) have not been studied with large samples. In particular, it is unclear the extent to which carbon-chain species form around them. Aims. We aim to obtain the chemical compositions of a sample of IM protostars, focusing particularly on carbon-chain species. We also aim to derive the rotational temperatures of HC₅N to confirm whether carbon-chain species are formed in the warm gas around these stars. Methods. We conducted Q-band (31.5–50 GHz) line survey observations toward 11 mainly IM protostars with the Yebes 40 m radio telescope. The target protostars were selected from a subsample of the source list of the SOFIA Massive Star Formation project. Assuming local thermodynamic equilibrium, we derived the column densities of the detected molecules and the rotational temperatures of HC₅N and CH₃ OH. Results. Nine carbon-chain species (HC₃N, HC₅N, C₃H, C₄H linear-H₂CCC, cyclic-C₃H₂, CCS, C₃S, and CH₃CCH), three COMs (CH₃OH, CH₃CHO, and CH₃CN), H₂CCO, HNCO, and four simple sulfur-bearing species (¹³CS, C³⁴S, HCS⁺, and H₂CS) are detected. The rotational temperatures of HC₅N are derived to be ~20–30 K in three IM protostars (Cepheus E, HH288, and IRAS 20293+3952). The rotational temperatures of CH₃OH are derived in five IM sources and found to be similar to those of HC₅N. Conclusions. The rotational temperatures of HC₅N around the three IM protostars are very similar to those around low- and high-mass protostars. These results indicate that carbon-chain molecules are formed in lukewarm gas (~20–30 K) around IM protostars via the warm carbon-chain chemistry process. Thus, carbon-chain formation occurs ubiquitously in the warm gas around protostars across a wide range of stellar masses. Carbon-chain molecules and COMs coexist around most of the target IM protostars, which is similar to the situation for low- and high-mass protostars. In summary, the chemical characteristics around protostars are the same in the low-, intermediate- and high-mass regimes....

DOI： 10.1051/0004-6361/202451499

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

SO and SO₂ are two potential candidates to trace the different evolutionary phases of the low-mass star-formation process. Here, we report observations of SO and SO₂ along with their isotopologues, ³⁴SO and ³⁴SO_2, respectively, in four distinct phases of the low-mass star-formation process (prestellar core, first hydrostatic core, Class 0, and Class I) with an unbiased survey carried out using the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope. Interestingly, the estimated abundances of SO and SO₂ show an increasing trend from the prestellar phase to the Class 0 stage and then a decrease in the Class I phase. A similar trend is obtained for OCS and H₂S. In contrast, the obtained SO/SO₂ ratio decreases gradually from the prestellar core to the Class I stage. We have used the three-phase Rokko chemical code to explain our observations. The modeled abundances of SO and SO₂ exhibit an increase within the inner region as the cold gas transforms into a hot gas. The modeled abundance ratio of SO to SO₂ exhibits a notably high value in cold gas environments. This ratio decreases to less than 1 within the temperature range of 100–300 K and then increases to approximately 1 beyond 300 K. In the outer region, the simulated ratio consistently exceeds the value of 1. Our work is an observational testbed for modeling the chemistry of SO/SO₂ during low-mass star formation. However, our findings may require more sample sources with higher resolution and a more robust model for validation.

DOI： 10.3389/fspas.2024.1427048

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

Massive protostars launch accretion-powered, magnetically-collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free-free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We post-process 3D magneto-hydrodynamic simulation snapshots of a protostellar disk wind interacts with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free-free emission. We find heating up to ~10^7 K and near complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ~10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ~10 to 100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10-year radio flux variability of ~5%, especially in the inner 1000 au region, comparable to observed levels in some hyper-compact HII regions....

DOI： 10.3847/1538-4357/ad39e1

arXiv

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Publishing type：Research paper (scientific journal)  

Massive protostars launch accretion-powered, magnetically collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free–free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We postprocess 3D magnetohydrodynamic simulation snapshots of a protostellar disk wind interacting with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free–free emission. We find heating up to ∼10⁷ K and near-complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ∼10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio-continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low- and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ∼10–100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10 yr radio flux variability of ∼5%, especially in the inner 1000 au region, comparable to observed levels in some hypercompact H II regions....

DOI： 10.3847/1538-4357/ad39e1

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

To test theoretical models of massive star formation it is important to compare their predictions with observed systems. To this end, we conduct CO molecular line radiative transfer post-processing of 3D magneto-hydrodynamic (MHD) simulations of various stages in the evolutionary sequence of a massive protostellar core, including its infall envelope and disk wind outflow. Synthetic position-position-velocity (PPV) cubes of various transitions of CO, 13CO, and C18O emission are generated. We also carry out simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations of this emission. We compare the mass, momentum and kinetic energy estimates obtained from molecular lines to the true values, finding that the mass and momentum estimates can have uncertainties of up to a factor of four. However, the kinetic energy estimated from molecular lines is more significantly underestimated. Additionally, we compare the mass outflow rate and momentum outflow rate obtained from the synthetic spectra with the true values. Finally, we compare the synthetic spectra with real examples of ALMA-observed protostars and determine the best fitting protostellar masses and outflow inclination angles. We then calculate the mass outflow rate and momentum outflow rate for these sources, finding that both rates closely match theoretical protostellar evolutionary tracks....

DOI： 10.3847/1538-4357/ad3211

arXiv

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Publishing type：Research paper (scientific journal)  

To test theoretical models of massive star formation it is important to compare their predictions with observed systems. To this end, we conduct CO molecular line radiative transfer post-processing of 3D magnetohydrodynamic simulations of various stages in the evolutionary sequence of a massive protostellar core, including its infall envelope and disk wind outflow. Synthetic position–position–velocity cubes of various transitions of ¹²CO, ¹³CO, and C¹⁸O emission are generated. We also carry out simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations of this emission. We compare the mass, momentum, and kinetic energy estimates obtained from molecular lines to the true values, finding that the mass and momentum estimates can have uncertainties of up to a factor of 4. However, the kinetic energy estimated from molecular lines is more significantly underestimated. Additionally, we compare the mass outflow rate and momentum outflow rate obtained from the synthetic spectra with the true values. Finally, we compare the synthetic spectra with real examples of ALMA-observed protostars and determine the best-fitting protostellar masses and outflow inclination angles. We then calculate the mass outflow rate and momentum outflow rate for these sources, finding that both rates agree with theoretical protostellar evolutionary tracks....

DOI： 10.3847/1538-4357/ad3211

arXiv

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Publishing type：Research paper (scientific journal)  

Context. Massive stars play important roles throughout the universe; however, their formation remains poorly understood. Observations of jets and outflows in high-mass star-forming regions, as well as surveys of young stellar object (YSO) content, can help test theoretical models of massive star formation. <BR /> Aims: We aim at characterizing the massive star-forming region AFGL 5180 in the near-infrared (NIR), identifying outflows and relating these to sub-mm/mm sources, as well as surveying the overall YSO surface number density to compare to massive star formation models. <BR /> Methods: Broad- and narrow-band imaging of AFGL 5180 was made in the NIR with the Large Binocular Telescope, in both seeing-limited (~0.5″) and high angular resolution (~0.09″) Adaptive Optics (AO) modes, as well as with the Hubble Space Telescope. Archival continuum data from the Atacama Millimeter/Submillimeter Array (ALMA) was also utilized. <BR /> Results: At least 40 jet knots were identified via NIR emission from H₂ and [FeII] tracing shocked gas. Bright jet knots outflowing from the central most massive protostar, S4 (estimated mass ~11 M_⊙, via SED fitting), are detected towards the east of the source and are resolved in fine detail with the AO imaging. Additional knots are distributed throughout the field, likely indicating the presence of multiple driving sources. Sub-millimeter sources detected by ALMA are shown to be grouped in two main complexes, AFGL 5180 M and a small cluster ~15″ (0.15 pc in projection) to the south, AFGL 5180 S. From our NIR continuum images we identify YSO candidates down to masses of ~0.1 M_⊙. Combined with the sub-mm sources, this yields a surface number density of such YSOs of N_* ~ 10³pc⁻² within a projected radius of about 0.1 pc. Such a value is similar to those predicted by models of both core accretion from a turbulent clump environment and competitive accretion. The radial profile of N_* is relatively flat on scales out to 0.2 pc, with only modest enhancement around the massive protostar inside 0.05 pc, which provides additional constraints on these massive star formation models. <BR /> Conclusions: This study demonstrates the utility of high-resolution NIR imaging, in particular with AO, for detecting outflow activity and YSOs in distant regions. The presented images reveal the complex morphology of outflow-shocked gas within the large-scale bipolar flow of a massive protostar, as well as clear evidence for several other outflow driving sources in the region. Finally, this work presents a novel approach to compare the observed YSO surface number density from our study against different models of massive star formation. <P />The reduced images are available at the CDS via anonymous ftp to <A href="https://cdsarc.cds.unistra.fr">cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href="https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A2">https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A2</A>...

DOI： 10.1051/0004-6361/202348094

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from ALMA 1.3~mm observations with resolution of 0.2 arcsec ($\sim$1,000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., $\rm{H_2CO}$, $\rm{CH_3OH}$, $\rm{CH_3OCH_3}$), sulfur-bearing (SO$_2$, H$_2$S) and nitrogen-bearing (e.g., HNCO, NH$_2$CHO, C$_2$H$_3$CN, C$_2$H$_5$CN) molecules. We discuss their spatial distributions, physical conditions, correlation between different species and possible chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 is part of a mm continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of $\sim300\:$K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of $\sim250\:$K, and is of intermediate chemical complexity. HMC3 is further away, $\sim3,000\:$au in projection, cooler ($\sim70\:$K) and is the least line-rich. The three HMCs have similar mass surface densities ($\sim10\:{\rm{g\:cm } }^{-2}$), number densities ($n_{\rm H}\sim10^9\:{\rm{cm } }^{-3}$) and masses of a few $M_\odot$. The total gas mass in the cores and in the region out to $3,000\:$au is $\sim 25\:M_\odot$, which is comparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities and abundances of the detected species and discuss the implications for hot core astrochemistry....

DOI： 10.3847/1538-4357/ad09bb

arXiv

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Publishing type：Research paper (scientific journal)  

We report the first extragalactic detection of the higher-order millimeter hydrogen recombination lines (Δn &gt; 2). The γ-, ϵ-, and η-transitions have been detected toward the millimeter continuum source N 105-1 A in the star-forming region N 105 in the Large Magellanic Cloud with the Atacama Large Millimeter/submillimeter Array. We use the H40α line, the brightest of the detected recombination lines (H40α, H36β, H50β, H41γ, H57γ, H49ϵ, H53η, and H54η), to determine the electron temperature and study ionized gas kinematics in the region, and the 3 mm free-free continuum emission to determine the physical parameters: the size, emission measure, and electron density. We compare the physical properties of N 105-1 A to a large sample of Galactic compact and ultracompact (UC) H II regions and conclude that N 105-1 A is similar to the most luminous (L &gt; 10⁵ L _⊙) UC H II regions in the Galaxy. N 105-1 A is ionized by an O5.5 V star; it is deeply embedded in its natal molecular clump, and likely associated with a (proto)cluster. We incorporate high-resolution molecular line data including CS, SO, SO₂, and CH₃OH (~0.12 pc), and HCO⁺ and CO (~0.087 pc) to explore the molecular environment of N 105-1 A. Based on the CO data, we find evidence for a cloud-cloud collision that likely triggered star formation in the region. We find no clear outflow signatures, but the presence of filaments and streamers indicates ongoing accretion onto the clump hosting the UC H II region. Sulfur chemistry in N 105-1 A is consistent with the accretion shock model predictions....

DOI： 10.3847/1538-4357/acf5ed

arXiv

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Publishing type：Research paper (scientific journal)  

The destiny of complex organic molecules (COMs) in star-forming regions is interlinked with various evolutionary phases. Therefore, identifying these species in diversified environments of identical star-forming regions would help to understand their physical and chemical heritage. We identified multiple COMs utilizing the Large Program Astrochemical Surveys At Institut de Radio Astronomie Millimétrique (IRAM) data, dedicated to chemical surveys in Sun-like star-forming regions with the IRAM 30 m telescope. It was an unbiased survey in the millimeter regime, covering the prestellar core, protostar, outflow region, and protoplanetary disk phase. Here, we report the transitions of seven COMs, namely, methanol (CH₃OH), acetaldehyde (CH₃CHO), methyl formate (CH₃OCHO), ethanol (C₂H₅OH), propynal (HCCCHO), dimethyl ether (CH₃OCH₃), and methyl cyanide (CH₃CN) in sources L1544, B1-b, IRAS4A, and SVS13A. We found a trend among these species from the derived abundances using the rotational diagram method and Monte Carlo Markov chain fitting. We have found that the abundances of all of the COMs, except for HCCCHO, increase from the L1544 (prestellar core) and peaks at IRAS16293-2422 (class 0 phase). It is noticed that the abundance of these molecules correlates with the luminosity of the sources. The obtained trend is also visible from the previous interferometric observations and considering the beam dilution effect....

DOI： 10.3847/1538-4357/acfc4d

arXiv

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

Abstract

Recent millimeter/submillimeter facilities have revealed the physical properties of filamentary molecular clouds in relation to high-mass star formation. A uniform survey of the nearest, face-on star-forming galaxy, the Large Magellanic Cloud (LMC), complements the Galactic knowledge. We present ALMA survey data with a spatial resolution of ∼0.1 pc in the 0.87 mm continuum and HCO⁺ (4–3) emission toward 30 protostellar objects with luminosities of 10⁴–10^5.5L_⊙ in the LMC. The spatial distributions of the HCO⁺ (4–3) line and thermal dust emission are well correlated, indicating that the line effectively traces dense, filamentary gas with an H₂ volume density of ≳10⁵ cm⁻³ and a line mass of ∼10³–10⁴M_⊙ pc⁻¹. Furthermore, we obtain an increase in the velocity line widths of filamentary clouds, which follows a power-law dependence on their H₂ column densities with an exponent of ∼0.5. This trend is consistent with observations toward filamentary clouds in nearby star-forming regions within ≲1 kpc from us and suggests enhanced internal turbulence within the filaments due to surrounding gas accretion. Among the 30 sources, we find that 14 are associated with hub-filamentary structures, and these complex structures predominantly appear in protostellar luminosities exceeding ∼5 × 10⁴L_⊙. The hub-filament systems tend to appear in the latest stages of their natal cloud evolution, often linked to prominent H ii regions and numerous stellar clusters. Our preliminary statistics suggest that the massive filaments accompanied by hub-type complex features may be a necessary intermediate product in forming extremely luminous high-mass stellar systems capable of ultimately dispersing the parent cloud.

DOI： 10.3847/1538-4357/acefb7

arXiv

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acefb7/pdf

Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ACF5ED

Web of Science

arXiv

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Publishing type：Research paper (scientific journal)  

DOI： 10.48550/arXiv.2303.09148

DOI： 10.3847/1538-4357/acc52f

arXiv

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Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/acc52f

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Publishing type：Research paper (scientific journal)  

Typical accretion disks around massive protostars are hot enough for water ice to sublimate. We here propose to utilize the massive protostellar disks for investigating the collisional evolution of silicate grains with no ice mantle, which is an essential process for the formation of rocky planetesimals in protoplanetary disks around lower-mass stars. We, for the first time, develop a model of massive protostellar disks that includes the coagulation, fragmentation, and radial drift of dust. We show that the maximum grain size in the disks is limited by collisional fragmentation rather than by radial drift. We derive analytic formulae that produce the radial distribution of the maximum grain size and dust surface density in the steady state. Applying the analytic formulae to the massive protostellar disk of GGD27-MM1, where the grain size is constrained from a millimeter polarimetric observation, we infer that the silicate grains in this disk fragment at collision velocities above ≈10 m s^-1. The inferred fragmentation threshold velocity is lower than the maximum grain collision velocity in typical protoplanetary disks around low-mass stars, implying that coagulation alone may not lead to the formation of rocky planetesimals in those disks. With future measurements of grain sizes in massive protostellar disks, our model will provide more robust constraints on the sticking property of silicate grains....

DOI： 10.3847/1538-4357/acc52f

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We report the first detection of hot molecular cores in the Small Magellanic Cloud, a nearby dwarf galaxy with 0.2 solar metallicity. We observed two high-mass young stellar objects in the SMC with ALMA, and detected emission lines of CO, HCO+, H13CO+, SiO, H2CO, CH3OH, SO, and SO2. Compact hot-core regions are traced by SO2, whose spatial extent is about 0.1 pc, and the gas temperature is higher than 100 K based on the rotation diagram analysis. In contrast, CH3OH, a classical hot-core tracer, is dominated by extended (0.2-0.3 pc) components in both sources, and the gas temperature is estimated to be 39+-8 K for one source. Protostellar outflows are also detected from both sources as high-velocity components of CO. The metallicity-scaled abundances of SO2 in hot cores are comparable among the SMC, LMC, and Galactic sources, suggesting that the chemical reactions leading to SO2 formation would be regulated by elemental abundances. On the other hand, CH3OH shows a large abundance variation within SMC and LMC hot cores. The diversity in the initial condition of star formation (e.g., degree of shielding, local radiation field strength) may lead to the large abundance variation of organic molecules in hot cores. This work, in conjunction with previous hot-core studies in the LMC and outer/inner Galaxy, suggests that the formation of a hot core would be a common phenomenon during high-mass star formation across the metallicity range of 0.2-1 solar metallicity. High-excitation SO2 lines will be a useful hot-core tracer in the low-metallicity environments of the SMC and LMC....

DOI： 10.3847/2041-8213/acc031

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

Star formation is ubiquitously associated with the ejection of accretion-powered outflows that carve bipolar cavities through the infalling envelope. This feedback is expected to be important for regulating the efficiency of star formation from a natal pre-stellar core. These low-extinction outflow cavities greatly affect the appearance of a protostar by allowing the escape of shorter wavelength photons. Doppler-shifted CO line emission from outflows is also often the most prominent manifestation of deeply embedded early-stage star formation. Here, we present 3D magneto-hydrodynamic simulations of a disk wind outflow from a protostar forming from an initially $60\:M_\odot$ core embedded in a high pressure environment typical of massive star-forming regions. We simulate the growth of the protostar from $m_*=1\:M_\odot$ to $26\:M_\odot$ over a period of $\sim$100,000 years. The outflow quickly excavates a cavity with half opening angle of $\sim10^\circ$ through the core. This angle remains relatively constant until the star reaches $4\:M_\odot$. It then grows steadily in time, reaching a value of $\sim 50^\circ$ by the end of the simulation. We estimate a lower limit to the star formation efficiency (SFE) of 0.43. However, accounting for continued accretion from a massive disk and residual infall envelope, we estimate that the final SFE may be as high as $\sim0.7$. We examine observable properties of the outflow, especially the evolution of the cavity opening angle, total mass and momentum flux, and velocity distributions of the outflowing gas, and compare with the massive protostars G35.20-0.74N and G339.88-1.26 observed by ALMA, yielding constraints on their intrinsic properties....

DOI： 10.3847/1538-4357/acbd47

arXiv

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Publishing type：Research paper (scientific journal)  

Star formation is ubiquitously associated with the ejection of accretion-powered outflows that carve bipolar cavities through the infalling envelope. This feedback is expected to be important for regulating the efficiency of star formation from a natal prestellar core. These low-extinction outflow cavities greatly affect the appearance of a protostar by allowing the escape of shorter-wavelength photons. Doppler-shifted CO line emission from outflows is also often the most prominent manifestation of deeply embedded early-stage star formation. Here, we present 3D magnetohydrodynamic simulations of a disk wind outflow from a protostar forming from an initially 60 M _⊙ core embedded in a high-pressure environment typical of massive star-forming regions. We simulate the growth of the protostar from m _* = 1 M _⊙ to 26 M _⊙ over a period of ~100,000 yr. The outflow quickly excavates a cavity with a half opening angle of ~10° through the core. This angle remains relatively constant until the star reaches 4 M _⊙. It then grows steadily in time, reaching a value of ~50° by the end of the simulation. We estimate a lower limit to the star formation efficiency (SFE) of 0.43. However, accounting for continued accretion from a massive disk and residual infall envelope, we estimate that the final SFE may be as high as ~0.7. We examine observable properties of the outflow, especially the evolution of the cavity's opening angle, total mass, and momentum flux, and the velocity distributions of the outflowing gas, and compare with the massive protostars G35.20-0.74N and G339.88-1.26 observed by the Atacama Large Millimeter/submillimeter Array (ALMA), yielding constraints on their intrinsic properties....

DOI： 10.3847/1538-4357/acbd47

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

Molecular lines tracing the orbital motion of gas in a well-defined disk are valuable tools for inferring both the properties of the disk and the star it surrounds. Lines that arise only from a disk, and not also from the surrounding molecular cloud core that birthed the star or from the outflow it drives, are rare. Several such emission lines have recently been discovered in one example case, those from NaCl and KCl salt molecules. We studied a sample of 23 candidate high-mass young stellar objects (HMYSOs) in 17 high-mass star-forming regions to determine how frequently emission from these species is detected. We present five new detections of water, NaCl, KCl, PN, and SiS from the innermost regions around the objects, bringing the total number of known briny disk candidates to nine. Their kinematic structure is generally disk-like, though we are unable to determine whether they arise from a disk or outflow in the sources with new detections. We demonstrate that these species are spatially coincident in a few resolved cases and show that they are generally detected together, suggesting a common origin or excitation mechanism. We also show that several disks around HMYSOs clearly do not exhibit emission in these species. Salty disks are therefore neither particularly rare in high-mass disks, nor are they ubiquitous....

DOI： 10.3847/1538-4357/ac9f4a

arXiv

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Publishing type：Research paper (scientific journal)  

Molecular lines tracing the orbital motion of gas in a well-defined disk are valuable tools for inferring both the properties of the disk and the star it surrounds. Lines that arise only from a disk, and not also from the surrounding molecular cloud core that birthed the star or from the outflow it drives, are rare. Several such emission lines have recently been discovered in one example case, those from NaCl and KCl salt molecules. We studied a sample of 23 candidate high-mass young stellar objects (HMYSOs) in 17 high-mass star-forming regions to determine how frequently emission from these species is detected. We present five new detections of water, NaCl, KCl, PN, and SiS from the innermost regions around the objects, bringing the total number of known briny disk candidates to nine. Their kinematic structure is generally disk-like, though we are unable to determine whether they arise from a disk or outflow in the sources with new detections. We demonstrate that these species are spatially coincident in a few resolved cases and show that they are generally detected together, suggesting a common origin or excitation mechanism. We also show that several disks around HMYSOs clearly do not exhibit emission in these species. Salty disks are therefore neither particularly rare in high-mass disks, nor are they ubiquitous....

DOI： 10.3847/1538-4357/ac9f4a

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We present $\sim10-40\,\mu$m \textit{SOFIA}-FORCAST images of 11 "isolated" protostars as part of the \textit{SOFIA} Massive (SOMA) Star Formation Survey, with this morphological classification based on 37\,$\mu$m imaging. We develop an automated method to define source aperture size based on the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, based on the Turbulent Core Accretion (TCA) theory, to estimate key protostellar properties. Here we release the \textit{sedcreator} python package that carries out these methods. The SEDs are generally well-fit by the TCA models, from which we infer initial core masses $M_c$ ranging from $50-430\:M_\odot$, clump mass surface densities $\Sigma_{\rm cl}\sim0.1-3\:{\rm{g\:cm } }^{-2}$ and current protostellar masses $m_*\sim2-40\:M_\odot$. From an uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold $\Sigma_{\rm cl}$ for massive star formation. However, the upper end of the $m_*-\Sigma_{\rm cl}$ distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher $\Sigma_{\rm cl}$ conditions. We also investigate protostellar FIR variability by comparison with IRAS data, finding no significant variation over a $\sim$40-year baseline....

DOI： 10.3847/1538-4357/aca4cf

arXiv

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Publishing type：Research paper (scientific journal)  

Young massive clusters (YMCs) are the most massive star clusters forming in nearby galaxies and are thought to be a young analogue to the globular clusters. Understanding the formation process of YMCs leads to looking into very efficient star formation in high-redshift galaxies suggested by recent JWST observations. We investigate possible observational signatures of their formation stage, particularly when the mass of a cluster is increasing via accretion from a natal molecular cloud. To this end, we study the broad-band continuum emission from ionized gas and dust enshrouding YMCs, whose formation is followed by recent radiation hydrodynamics simulations. We perform post-process radiative transfer calculations using simulation snapshots and find characteristic spectral features at radio and far-infrared frequencies. We show that a striking feature is long-lasting, strong free-free emission from a ~10-pc-scale H II region with a large emission measure of ≳10⁷ cm^-6 pc, corresponding to the mean electron density of ≳10³ cm^-3. There is a turnover feature below ~10 GHz, a signature of the optically thick free-free emission, often found in Galactic ultracompact H II regions. These features come from the peculiar YMC formation process, where the cluster's gravity effectively traps photoionized gas for a long duration and enables continuous star formation within the cluster. Such large and dense H II regions show distinct distribution on the density-size diagram, apart from the standard sequence of Galactic H II regions. This is consistent with the observational trend inferred for extragalactic H II regions associated with YMCs....

DOI： 10.1093/mnras/stad3297

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press (CUP)  

Abstract

We report on a direct comparison of VLBI maser data and ALMA thermal-emission data for the high-mass protostar G353.273+0.641. We detected a gravitationally-unstable disk by dust and a high-velocity jet traced by a thermal CO line by ALMA long-baselines (LB). 6.7 GHz CH₃OH masers trace infalling streamlines inside the disk. The innermost maser ring indicates another compact accretion disk of 30 au. Such a nested system could be caused by angular momentum transfer by the spiral arms. 22 GHz H₂O masers trace the jet-accelerating region, which are directly connecting the CO jet and the protostar. The recurrent maser flares imply episodic jet ejections per 1–2 yr, while typical separation of CO knots indicates a variation of outflow rate per 100 yr. Our study demonstrates that VLBI maser observations are still a powerful tool to explore detailed structures nearby high-mass protostars by combining ALMA LB.

DOI： 10.1017/s1743921323003216

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Publishing type：Research paper (scientific journal)  

We report high-resolution 1.3 mm continuum and molecular line observations of the massive protostar G28.20-0.05 with Atacama Large Millimeter/submillimeter Array. The continuum image reveals a ring-like structure with 2000 au radius, similar to morphology seen in archival 1.3 cm Very Large Array observations. Based on its spectral index and associated H30α emission, this structure mainly traces ionized gas. However, there is evidence for ~30 M _⊙ of dusty gas near the main millimeter continuum peak on one side of the ring, as well as in adjacent regions within 3000 au. A virial analysis on scales of ~2000 au from hot core line emission yields a dynamical mass of ~80 M _⊙. A strong velocity gradient in the H30α emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared spectral energy distribution (SED) analysis indicates a current protostellar mass of m _* ~ 40 M _⊙ forming from a core with initial mass M _c ~ 300 M _⊙ in a clump with mass surface density of Σ_cl ~ 0.8 g cm^-2. Thus the SED and other properties of the system can be understood in the context of core accretion models. A structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ~1 M _⊙ found from ~0.1 to 0.4 pc around the source. This implies that a massive star can form in relative isolation, and the dearth of other protostellar companions within the ~1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster....

DOI： 10.3847/1538-4357/ac90c7

arXiv

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Publishing type：Research paper (scientific journal)  

Cosmic metallicity evolution possibly creates the diversity of star formation modes at different epochs. Gravitational fragmentation of circumstellar discs provides an important formation channel of multiple star systems, including close binaries. We here study the nature of disc fragmentation, systematically performing a suite of 2D radiation-hydrodynamic simulations, in a broad range of metallicities, from the primordial to the solar values. In particular, we follow relatively long-term disc evolution over 15 kyr after the disc formation, incorporating the effect of heating by the protostellar irradiation. Our results show that the disc fragmentation occurs at all metallicities 1-$0 \, \rm {Z}_{\odot }$, yielding self-gravitating clumps. Physical properties of the clumps, such as their number and mass distributions, change with the metallicity due to different gas thermal evolution. For instance, the number of clumps is the largest for the intermediate metallicity range of 10^-2-$10^{-5} \, \rm {Z}_{\odot }$, where the dust cooling is effective exclusively in a dense part of the disc and causes the fragmentation of spiral arms, although the disc might fragment at a similar rate, also at lower metallicities 10^-6-$0 \, \rm {Z}_{\odot }$ with higher spatial resolution. The disc fragmentation is more modest for 1-$0.1 \, \rm {Z}_{\odot }$, thanks to the disc stabilization by the stellar irradiation. Such metallicity dependence agrees with the observed trend that the close binary fraction increases with decreasing metallicity in the range of 1-$10^{-3} \, \rm {Z}_{\odot }$....

DOI： 10.1093/mnras/stac2161

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

Cosmic metallicity evolution possibly creates the diversity of star formation modes at different epochs. Gravitational fragmentation of circumstellar discs provides an important formation channel of multiple star systems, including close binaries. We here study the nature of disc fragmentation, systematically performing a suite of two-dimensional radiation-hydrodynamic simulations, in a broad range of metallicities, from the primordial to the solar values. In particular, we follow relatively long-term disc evolution over 15 kyr after the disc formation, incorporating the effect of heating by the protostellar irradiation. Our results show that the disc fragmentation occurs at all metallicities $1$--$0$ $Z_{\odot}$, yielding self-gravitating clumps. Physical properties of the clumps, such as their number and mass distributions, change with the metallicity due to different gas thermal evolution. For instance, the number of clumps is the largest for the intermediate metallicity range of $10^{-2}$--$10^{-5}$ $Z_{\odot}$, where the dust cooling is effective exclusively in a dense part of the disc and causes the fragmentation of spiral arms. The disc fragmentation is more modest for $1$--$0.1$ $Z_{\odot}$ thanks to the disc stabilization by the stellar irradiation. Such metallicity dependence agrees with the observed trend that the close binary fraction increases with decreasing metallicity in the range of $1$--$10^{-3}$ $Z_{\odot}$....

DOI： 10.1093/mnras/stac2161

arXiv

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

DOI： 10.3847/2041-8213/ac81c1

Web of Science

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We present a detailed study of the massive star-forming region G35.2-0.74N with ALMA 1.3 mm multi-configuration observations. At 0.2" (440 au) resolution, the continuum emission reveals several dense cores along a filamentary structure, consistent with previous ALMA 0.85 mm observations. At 0.03" (66 au) resolution, we detect 22 compact sources, most of which are associated with the filament. Four of the sources are associated with compact centimeter continuum emission, and two of these are associated with H30{\alpha} recombination line emission. The H30{\alpha} line kinematics show ordered motion of the ionized gas, consistent with disk rotation and/or outflow expansion. We construct models of photoionized regions to simultaneously fit the multi-wavelength free-free fluxes and the H30{\alpha} total fluxes. The derived properties suggest the presence of at least three massive young stars with nascent hypercompact Hii regions. Two of these ionized regions are surrounded by a large rotating structure that feeds two individual disks, revealed by dense gas tracers, such as SO2, H2CO, and CH3OH. In particular, the SO2 emission highlights two spiral structures in one of the disks and probes the faster-rotating inner disks. The 12CO emission from the general region reveals a complex outflow structure, with at least four outflows identified. The remaining 18 compact sources are expected to be associated with lower-mass protostars forming in the vicinity of the massive stars. We find potential evidence for disk disruption due to dynamical interactions in the inner region of this protocluster. The spatial distribution of the sources suggests a smooth overall radial density gradient without subclustering, but with tentative evidence of primordial mass segregation....

DOI： 10.3847/1538-4357/ac847f

arXiv

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Publishing type：Research paper (scientific journal)  

Massive dense clumps in the Large Magellanic Cloud can be an important laboratory to explore the formation of populous clusters. We report multiscale ALMA observations of the N159W-North clump, which is the most CO-intense region in the galaxy. High-resolution CO isotope and 1.3 mm continuum observations with an angular resolution of ~0.″25 (~0.07 pc) revealed more than five protostellar sources with CO outflows within the main ridge clump. One of the thermal continuum sources, MMS-2, shows an especially massive/dense nature whose total H₂ mass and peak column density are ~10⁴ M _⊙ and ~10²⁴ cm^-2, respectively, and harbors massive (~100 M _⊙) starless core candidates identified as its internal substructures. The main ridge containing this source can be categorized as one of the most massive protocluster systems in the Local Group. The CO high-resolution observations found several distinct filamentary clouds extending southward from the star-forming spots. The CO (1-0) data set with a larger field of view reveals a conical, ~30 pc long complex extending toward the northern direction. These features indicate that a large-scale gas compression event may have produced the massive star-forming complex. Based on the striking similarity between the N159W-North complex and the other two previously reported high-mass star-forming clouds in the nearby regions, we propose a "teardrops inflow model" that explains the synchronized, extreme star formation across &gt;50 pc, including one of the most massive protocluster clumps in the Local Group....

DOI： 10.3847/1538-4357/ac6b3c

arXiv

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

DOI： 10.3847/2041-8213/ac81c1

Web of Science

arXiv

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

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 (v ₇ = 2, J = 24 - 23). The spatial distribution and kinematics of a vibrationally excited line of HC₃N (v ₇ = 2, J = 24 - 23, l = 2e) are found to be similar to the CH₃CN vibrationally excited line (v ₈ = 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

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

Publisher：arXiv e-prints  

Massive dense clumps in the Large Magellanic Cloud can be an important laboratory to explore the formation of populous clusters. We report multiscale ALMA observations of the N159W-North clump, which is the most CO-intense region in the galaxy. High-resolution CO isotope and 1.3 mm continuum observations with an angular resolution of $\sim$0."25($\sim$0.07 pc) revealed more than five protostellar sources with CO outflows within the main ridge clump. One of the thermal continuum sources, MMS-2, shows especially massive/dense nature whose total H$_2$ mass and peak column density are $\sim$10$^{4}$ $M_{\odot}$ and $\sim$10$^{24}$ cm$^{-2}$, respectively, and harbors massive ($\sim$100 $M_{\odot}$) starless core candidates identified as its internal substructures. The main ridge containing this source can be categorized as one of the most massive protocluster systems in the Local Group. The CO high-resolution observations found several distinct filamentary clouds extending southward from the star-forming spots. The CO (1-0) data set with a larger field of view reveals a conical-shaped, $\sim$30 pc long complex extending toward the northern direction. These features indicate that a large-scale gas compression event may have produced the massive star-forming complex. Based on the striking similarity between the N159W-North complex and the previously reported other two high-mass star-forming clouds in the nearby regions, we propose a $"$teardrops inflow model$"$ that explains the synchronized, extreme star formation across $>$50 pc, including one of the most massive protocluster clumps in the Local Group....

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of the hyper-compact H$_{\rm {II } }$ region G24.78+0.08 A1 (G24 HC H$_{\rm {II } }$) and report the detection of vibrationally-excited lines of HC$_{3}$N ($v_{7}=2$, $J=24-23$). The spatial distribution and kinematics of a vibrationally-excited line of HC$_{3}$N ($v_{7}=2$, $J=24-23$, $l=2e$) are found to be similar to the CH$_{3}$CN vibrationally-excited line ($v_{8}=1$), which indicates that the HC$_{3}$N emission is tracing the disk around the G24 HC H$_{\rm {II } }$ region previously identified by the CH$_{3}$CN lines. We derive the $^{13}$CH$_{3}$CN/HC$^{13}$CCN abundance ratios around G24 and compare them to the CH$_{3}$CN/HC$_{3}$N abundance ratios in disks around Herbig Ae and T Tauri stars. The $^{13}$CH$_{3}$CN/HC$^{13}$CCN ratios around G24 ($\sim 3.0-3.5$) are higher than the CH$_{3}$CN/HC$_{3}$N ratios in the other disks ($\sim 0.03-0.11$) by more than one order of magnitude. The higher CH$_{3}$CN/HC$_{3}$N ratios around G24 suggest that the thermal desorption of CH$_{3}$CN in the hot dense gas and efficient destruction of HC$_{3}$N in the region irradiated by the strong UV radiation are occurring. Our results indicate that the vibrationally-excited HC$_{3}$N lines can be used as a disk tracer of massive protostars at the HC H$_{\rm {II } }$ 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

arXiv

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

Publisher：arXiv e-prints  

We report high-resolution 1.3mm continuum and molecular line observations of the massive protostar G28.20-0.05 with ALMA. The continuum image reveals a ring-like structure with 2,000 au radius, similar to morphology seen in archival 1.3cm VLA observations. Based on its spectral index and associated H30$\alpha$ emission, this structure mainly traces ionized gas. However, there is evidence for $\sim$30 M$\odot$ of dusty gas near the main mm continuum peak on one side of the ring, as well as in adjacent regions within 3,000 au. A virial analysis on scales of $\sim$2,000 au from hot core line emission yields a dynamical mass of $\sim$80M$\odot$. A strong velocity gradient in the H30$\alpha$ emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared SED analysis indicates a current protostellar mass of m$_{star}\sim$24 M$\odot$ forming from a core with initial mass $M_c\sim400\:M_\odot$ in a clump with mass surface density of $\Sigma_{\rm cl}\sim 3\:{\rm g\:cm}^{-2}$. Thus the SED and other properties of the system can be understood in the context of core accretion models. Structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above $\sim$ 1 M$\odot$ found from $\sim$0.1 to 0.4 pc around the source. This implies that a massive star is able to form in relative isolation and the dearth of other protostellar companions within the $\sim$1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster....

arXiv

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Publishing type：Research paper (scientific journal)  

We present ~10-40 μm SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 μm imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, developed within the framework of turbulent core accretion (TCA) theory, to estimate key protostellar properties. Here, we release the sedcreator python package that carries out these methods. The SEDs are generally well fitted by the TCA models, from which we infer initial core masses M _c ranging from 20-430 M _⊙, clump mass surface densities Σ_cl ~ 0.3-1.7 g cm^-2, and current protostellar masses m _* ~ 3-50 M _⊙. From a uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold Σ_cl for massive star formation. However, the upper end of the m _*-Σ_cl distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher Σ_cl conditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an ~40 yr baseline....

DOI： 10.3847/1538-4357/aca4cf

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

Multi-epoch narrow-band HST images of the bipolar Hii region Sh2-106 reveal highly supersonic nebular proper motions which increase with projected distance from the massive young stellar object S106~IR, reaching over ~30 mas/year (~150 km/s at D=1.09 kpc) at a projected separation of ~1.4' (0.44 pc) from S106~IR. We propose that S106~IR experienced a $\sim10^{47}$ erg explosion ~3,500 years ago. The explosion may be the result of a major accretion burst, a recent encounter with another star, or a consequence of the interaction of a companion with the bloated photosphere of S106~IR as it grew from ~10 through ~15 Solar masses at a high accretion rate. Near-IR images reveal fingers of molecular hydrogen emission pointing away from S106~IR and an asymmetric photon-dominated region surrounding the ionized nebula. Radio continuum and Brackett-gamma emission reveal a C-shaped bend in the plasma, either indicating motion of S106~IR toward the east, or deflection of plasma toward the west by the surrounding cloud. The Hii region bends around a ~1' diameter dark bay west of S106~IR that may be shielded from direct illumination by a dense molecular clump. Herbig-Haro (HH) and Molecular Hydrogen Objects (MHOs) tracing outflows powered by stars in the Sh2-106 proto-cluster such as the Class 0 source S106 FIR are discussed....

DOI： 10.3847/1538-4357/ac30de

arXiv

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Publishing type：Research paper (scientific journal)  

We present three-dimensional astrochemical simulations and synthetic observations of magnetised, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar medium environments, including cosmic-ray ionization rates in the range of ζ_CR = 10^-17-10^-14 s^-1, far-UV intensities in the range of G₀ = 1-10³ and metallicities in the range of Z = 0.1-2 Z_☉. The simulations also probe a range of densities and levels of turbulence, including cases where the gas has undergone recent compression due to cloud-cloud collisions. We examine: i) the column densities of carbon species across the cycle of C II, C I and CO, along with O I, in relation to the H I-to-H₂ transition; ii) the velocity-integrated emission of [C II] 158μm, [¹³C II] 158μm, [C I] 609μm and 370μm, [O I] 63μm and 146μm, and of the first ten ¹²CO rotational transitions; iii) the corresponding Spectral Line Energy Distributions; iv) the usage of [C II] and [O I] 63μm to describe the dynamical state of the clouds; v) the behavior of the most commonly used ratios between transitions of CO and [C I]; and vi) the conversion factors for using CO and C I as H₂-gas tracers. We find that enhanced cosmic-ray energy densities enhance all aforementioned line intensities. At low metallicities, the emission of [C II] is well connected with the H₂ column, making it a promising new H₂ tracer in metal-poor environments. The conversion factors of X_CO and X_CI depend on metallicity and the cosmic-ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA and the forthcoming CCAT-prime telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic environments....

DOI： 10.1093/mnras/stab121

arXiv

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Publishing type：Research paper (scientific journal)  

We present three-dimensional astrochemical simulations and synthetic observations of magnetized, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar medium environments, including cosmic ray ionization rates in the range of ζ_CR = 10^-17- $10^{-14}\, {\rm s}^{-1}$ , far-UV intensities in the range of G₀ = 1-10³ and metallicities in the range of Z = 0.1- $2\, {\rm Z}_{\odot }$ . The simulations also probe a range of densities and levels of turbulence, including cases where the gas has undergone recent compression due to cloud-cloud collisions. We examine: (i) the column densities of carbon species across the cycle of C II, C I, and CO, along with O I, in relation to the H I-to-H₂ transition; (ii) the velocity-integrated emission of [C II] 158 μm, [¹³C II] 158 μm, [C I] 609 μm and 370 μm, [O I] 63 μm and 146 μm, and of the first ten ¹²CO rotational transitions; (iii) the corresponding Spectral Line Energy Distributions; (iv) the usage of [C II] and [O I] 63 μm to describe the dynamical state of the clouds; (v) the behaviour of the most commonly used ratios between transitions of CO and [C I]; and (vi) the conversion factors for using CO and C I as H₂-gas tracers. We find that enhanced cosmic ray energy densities enhance all aforementioned line intensities. At low metallicities, the emission of [C II] is well connected with the H₂ column, making it a promising new H₂ tracer in metal-poor environments. The conversion factors of X_CO and X_{C I} depend on metallicity and the cosmic ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA, and the forthcoming CCAT-prime telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic environments....

DOI： 10.1093/mnras/stab121

arXiv

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Publisher：arXiv e-prints  

The Next Generation Very Large Array (ngVLA) has excellent capabilities to unveil various dynamical and chemical processes in massive star formation at the unexplored innermost regions. Based on the recent observations of ALMA/VLA as well as theoretical predictions, we propose several intriguing topics in massive star formation from the perspective of the ngVLA. In the disk scale of $\lesssim$ 100 au around massive protostars, dust grains are expected to be destructed/sublimated because the physical conditions of temperature, shocks, and radiation are much more intense than those in the envelopes, which are typically observed as hot cores. The high sensitivity and resolution of the ngVLA will enable us to detect the gaseous refractories released by dust destruction, e.g., SiO, NaCl, and AlO, which trace disk kinematics and give new insights into the metallic elements in star-forming regions, i.e., astromineralogy. The multi-epoch survey by the ngVLA will provide demographics of forming massive multiples with separations of $\lesssim$ 10 au with their proper motion. Combining with observations of refractory molecular lines and hydrogen recombination lines, we can reproduce the three-dimensional orbital motions of massive proto-binaries. Moreover, the 1-mas resolution of the ngVLA could possibly take the first-ever picture of the photospheric surface of an accreting protostar, if it is bloated to the au scale by the high accretion rates of mass and thermal energy....

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We systematically perform hydrodynamics simulations of 20 km s^-1 converging flows of the warm neutral medium (WNM) to calculate the formation of the cold neutral medium (CNM), especially focusing on the mean properties of the multiphase interstellar medium (ISM), such as the average shock front position and the mean density on a 10 pc scale. Our results show that the convergence in those mean properties requires 0.02 pc spatial resolution that resolves the cooling length of the thermally unstable neutral medium (UNM) to follow the dynamical condensation from the WNM to CNM. We also find that two distinct post-shock states appear in the mean properties depending on the amplitude of the upstream WNM density fluctuation (= sqrt(<drho^2>)/rho_0). When the amplitude > 10 %, the interaction between shocks and density inhomogeneity leads to a strong driving of the post-shock turbulence of > 3 km s^-1, which dominates the energy budget in the shock-compressed layer. The turbulence prevents the dynamical condensation by cooling and the following CNM formation, and the CNM mass fraction remains as ~ 45 %. In contrast, when the amplitude <= 10 %, the shock fronts maintain an almost straight geometry and CNM formation efficiently proceeds, resulting in the CNM mass fraction of ~ 70 %. The velocity dispersion is limited to the thermal-instability mediated level of 2 - 3 km s^-1 and the layer is supported by both turbulent and thermal energy equally. We also propose an effective equation of state that models the multiphase ISM formed by the WNM converging flow as a one-phase ISM....

DOI： 10.3847/1538-4357/abc5be

arXiv

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

We systematically perform hydrodynamics simulations of 20 $\mathrm{km}\,{ { \rm{s } } }^{-1}$ &lt;!-- --&gt; converging flows of the warm neutral medium (WNM) to calculate the formation of the cold neutral medium (CNM), focusing especially on the mean properties of the multiphase interstellar medium (ISM), such as the mean density on a 10 pc scale. Our results show that convergence in those mean properties requires a 0.02 pc spatial resolution that resolves the cooling length of the thermally unstable neutral medium (UNM) to follow the dynamical condensation from the WNM to the CNM. We also find that two distinct postshock states appear in the mean properties depending on the amplitude of the upstream WNM density fluctuation ${\rm{\Delta } }{\rho }_{0}$ &lt;!-- --&gt; ( $=\,\sqrt{\langle \delta {\rho }_{0}^{2}\rangle }{/\rho }_{0}$ &lt;!-- --&gt; ). When ${\rm{\Delta } }{\rho }_{0}\gt 10 \% $ &lt;!-- --&gt; , the interaction between shocks and density inhomogeneity leads to a strong driving of the postshock turbulence of &gt;3 km s^-1, which dominates the energy budget in the shock-compressed layer. The turbulence prevents dynamical condensation by cooling, and the CNM mass fraction remains at ∼45%. In contrast, when ${\rm{\Delta } }{\rho }_{0}\leqslant 10 \% $ &lt;!-- --&gt; , the CNM formation proceeds efficiently, resulting in the CNM mass fraction of ∼70%. The velocity dispersion is limited to the thermal-instability-mediated level of ∼2-3 km s^-1, and the layer is supported by both turbulent and thermal energy equally. We also propose an effective equation of state that models the multiphase ISM formed by the WNM converging flow as a one-phase ISM in the form of P ∝ ρ^γ_eff, where γ_eff varies from 0.9 (for a large pre-shock ∆ρ₀) to 0.7 (for a small pre-shock ∆ρ₀)....

DOI： 10.3847/1538-4357/abc5be

arXiv

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abc5be

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

We present multi-wavelength images observed with SOFIA-FORCAST from ~10 to 40 $\mu$m of 14 protostars, selected as intermediate-mass protostar candidates, as part of the SOFIA Massive (SOMA) Star Formation Survey. We build protostellar spectral energy distributions (SEDs) with the SOFIA observations, together with archival data from Spitzer, Herschel and IRAS. We then fit the SEDs with radiative transfer (RT) models of Zhang &amp; Tan (2018), based on Turbulent Core Accretion theory, to estimate key properties of the protostars. The SEDs generally indicate the validity of these RT models down to intermediate-mass and/or early-stage protostars. The protostars analyzed so far in the SOMA survey span a range of luminosities from ~$10^{2}$ to ~$10^{6} L_{\odot}$, current protostellar masses from ~0.5 to ~30 $M_{\odot}$, and ambient clump mass surface densities, $\Sigma_{\rm cl}$ of 0.1 - 3 g cm$^{-2}$. A wide range of evolutionary states of the individual protostars and of the protocluster environments are also probed. The 19 to 37 $\mu$m spectral index of the sources correlates with outflow cavity opening angle, ratio of this angle to viewing angle, and evolutionary stage. We have also added a sample of ~50 protostellar sources identified from within Infrared Dark Clouds and expected to be at the earliest stages of their evolution. With this global sample, most of the evolutionary stages of high- and intermediate-mass protostars are probed. From the best fitting models of the protostars, there is no evidence of a threshold value of protocluster clump mass surface density being needed to form protostars up to ~25 $M_\odot$. However, to form more massive protostars, there is tentative evidence that $\Sigma_{\rm cl}$ needs to be at least 1 g cm$^{-2}$. We discuss how this is consistent with expectations from core accretion models that include internal feedback from the forming massive star....

DOI： 10.3847/1538-4357/abbefb

arXiv

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

We present $\sim 10\mbox{--}40\,\mu {\rm{m } }$ SOFIA-FORCAST images of 14 intermediate-mass protostar candidates as part of the SOFIA Massive (SOMA) Star Formation Survey. We build spectral energy distributions, also using archival Spitzer, Herschel, and IRAS data. We then fit the spectral energy distributions with radiative transfer models of Zhang &amp; Tan, based on turbulent core accretion theory, to estimate key protostellar properties. With the addition of these intermediate-mass sources, based on average properties derived from SED fitting, SOMA protostars span luminosities from $\sim {10}^{2}\,\mathrm{to}\,{10}^{6}\ {L}_{\odot }$, current protostellar masses from $\sim 0.5\,{\rm{t } }{\rm{o } }\,35\,{M}_{\odot }$, and ambient clump mass surface densities, ${ { \rm{\Sigma } } }_{\mathrm{cl } }$ , from $0.1\,\mathrm{to}\,{\rm{g } }\,{\mathrm{cm } }^{-2}$. A wide range of evolutionary states of the individual protostars and of the protocluster environments is also probed. We have also considered about 50 protostars identified in infrared dark clouds that are expected to be at the earliest stages of their evolution. With this global sample, most of the evolutionary stages of high- and intermediate-mass protostars are probed. The best-fitting models show no evidence that a threshold value of the protocluster clump mass surface density is required to form protostars up to $\sim 25\ {M}_{\odot }$. However, to form more massive protostars, there is tentative evidence that ${ { \rm{\Sigma } } }_{\mathrm{cl } }$ needs to be $\gtrsim 1\,{\rm{g } }\,{\mathrm{cm } }^{-2}$. We discuss how this is consistent with expectations from core accretion models that include internal feedback from the forming massive star....

DOI： 10.3847/1538-4357/abbefb

arXiv

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

We report results of $0\buildrel{\prime\prime}\over{.} 05$-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array. We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows, and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000 au scale. The H₂O line tracing inner disks has an upper-state energy of ${E}_{u}/k\gt 3000\,{\rm{K } }$, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We posit that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest that these "hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547-4247....

DOI： 10.3847/2041-8213/abadfc

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

Through the magnetic braking and the launching of protostellar outflows, magnetic fields play a major role in the regulation of angular momentum in star formation, which directly impacts the formation and evolution of protoplanetary disks and binary systems. The aim of this paper is to quantify those phenomena in the presence of non-ideal magnetohydrodynamics effects, namely the Ohmic and ambipola r diffusion. We perform three-dimensional simulations of protostellar collapses varying the mass of the prestellar dense core, the thermal support (the $\alpha$ ratio) and the dust grain size-distribu tion. The mass mostly influences the magnetic braking in the pseudo-disk, while the thermal support impacts the accretion rate and hence the properties of the disk. Removing the grains smaller than 0. 1 $\mu$m in the Mathis, Rumpl, Nordsieck (MRN) distribution enhances the ambipolar diffusion coefficient. Similarly to previous studies, we find that this change in the distribution reduces the magnet ic braking with an impact on the disk. The outflow is also significantly weakened. In either case, the magnetic braking largely dominates the outflow as a process to remove the angular momentum from t he disk. Finally, we report a large ionic precursor to the outflow with velocities of several km s$^{-1}$, which may be observable....

DOI： 10.3847/1538-4357/abad99

arXiv

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Publishing type：Research paper (scientific journal)  

Through the magnetic braking and the launching of protostellar outflows, magnetic fields play a major role in the regulation of angular momentum in star formation, which directly impacts the formation and evolution of protoplanetary disks and binary systems. The aim of this paper is to quantify those phenomena in the presence of nonideal magnetohydrodynamics effects, namely, the ohmic and ambipolar diffusion. We perform three-dimensional simulations of protostellar collapses varying the mass of the prestellar dense core, the thermal support (the α ratio), and the dust grain size distribution. The mass mostly influences the magnetic braking in the pseudo-disk, while the thermal support impacts the accretion rate and hence the properties of the disk. Removing the grains smaller than 0.1 μm in the Mathis-Rumpl-Nordsieck distribution enhances the ambipolar diffusion coefficient. Similar to previous studies, we find that this change in the distribution reduces the magnetic braking with an impact on the disk. The outflow is also significantly weakened. In either case, the magnetic braking largely dominates the outflow as a process to remove the angular momentum from the disk. Finally, we report a large ionic precursor to the outflow with velocities of several km s^-1, which may be observable....

DOI： 10.3847/1538-4357/abad99

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

We report results of $0\buildrel{\prime\prime}\over{.} 05$-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array. We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows, and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000 au scale. The H₂O line tracing inner disks has an upper-state energy of ${E}_{u}/k\gt 3000\,{\rm{K } }$, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We posit that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest that these "hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547-4247....

DOI： 10.3847/2041-8213/abadfc

arXiv

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Publishing type：Research paper (scientific journal)  

We here present the results of 0.1 pc scale observations in 250 and 350 GHz toward a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected toward the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO₂ and ³⁴SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be ³²S/³⁴S = 17 and ³²S/³³S = 53 based on SO, SO₂, and CS isotopologues, suggesting that both ³⁴S and ³³S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (&gt;100 K) traced by high-excitation lines of CH₃OH and SO₂, as well as warm gas (∼50 K) traced by CH₃OH, SO₂, ³⁴SO, OCS, and CH₃CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH₃OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperatures during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO₂ shows similar abundances within all of the known LMC hot cores, and the typical abundance roughly scales with the LMC's metallicity. Nitrogen-bearing molecules are generally less abundant in the LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity....

DOI： 10.3847/1538-4357/ab6e6b

arXiv

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Publisher：arXiv e-prints  

We present the results of 0.1-pc-scale observations in 250 GHz and 350GHz towards a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected towards the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO2 and 34SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be 32S/34S = 17 and 32S/33S = 53 based on SO, SO2, and CS isotopologues, suggesting that both 34S and 33S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (>100K) traced by high-excitation lines of CH3OH and SO2, as well as warm gas (~50K) traced by CH3OH, SO2, 34SO, OCS, CH3CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH3OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperature during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO2 shows similar abundances within all the known LMC hot cores and the typical abundance roughly scales with the LMC's metallicity. Nitrogen-bearing molecules are generally less abundant in LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity....

DOI： 10.3847/1538-4357/ab6e6b

arXiv

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

DOI： 10.1088/1742-6596/1380/1/012057

Scopus

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

Massive protostars generate strong radiation feedback, which may help set the mass that they achieve by the end of the accretion process. Studying such feedback is therefore crucial for understanding the formation of massive stars. We report the discovery of a photoionized bipolar outflow toward the massive protostar G45.47+0.05 using high-resolution observations at 1.3 mm with the Atacama Large Millimeter/Submillimeter Array (ALMA) and at 7 mm with the Karl G. Jansky Very Large Array (VLA). By modeling the free─free continuum, the ionized outflow is found to be a photoevaporation flow with an electron temperature of 10,000 K and an electron number density of ∼1.5 × 10⁷ cm⁻³ at the center, launched from a disk of radius of 110 au. H30α hydrogen recombination line emission shows strong maser amplification, with G45 being one of very few sources to show such millimeter recombination line masers. The mass of the driving source is estimated to be 30─50 M _☉ based on the derived ionizing photon rate, or 30─40 M _☉ based on the H30α kinematics. The kinematics of the photoevaporated material is dominated by rotation close to the disk plane, while accelerated to outflowing motion above the disk plane. The mass loss rate of the photoevaporation outflow is estimated to be ∼(2─3.5) × 10⁻⁵ M _☉ yr⁻¹. We also found hints of a possible jet embedded inside the wide-angle ionized outflow with nonthermal emissions. The possible coexistence of a jet and a massive photoevaporation outflow suggests that, in spite of the strong photoionization feedback, accretion is still ongoing....

DOI： 10.3847/2041-8213/ab5309

arXiv

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Publishing type：Research paper (scientific journal)  

We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the outflow─core interaction for a massive protostar forming via collapse of an initial cloud core of 60 M _☉. This allows us to characterize the properties of disk-wind-driven outflows from massive protostars, which can allow testing of different massive star formation theories. It also enables us to assess quantitatively the impact of outflow feedback on protostellar core morphology and overall star formation efficiency (SFE). We find that the opening angle of the flow increases with increasing protostellar mass, in agreement with a simple semianalytic model. Once the protostar reaches ∼24 M_☉, the outflow’s opening angle is so wide that it has blown away most of the envelope, thereby nearly ending its own accretion. We thus find an overall SFE of ∼50%, similar to that expected from low-mass protostellar cores. Our simulation results therefore indicate that the MHD disk wind outflow is the dominant feedback mechanism for helping to shape the stellar initial mass function from a given prestellar core mass function....

DOI： 10.3847/1538-4357/ab36b3

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

We present multiwavelength images observed with SOFIA-FORCAST from ̃10 to 40 μm of seven high luminosity massive protostars, as part of the SOFIA Massive Star Formation Survey. Source morphologies at these wavelengths appear to be influenced by outflow cavities and extinction from dense gas surrounding the protostars. Using these images, we build spectral energy distributions (SEDs) of the protostars, also including archival data from Spitzer, Herschel, and other facilities. Radiative transfer (RT) models of Zhang &amp; Tan, based on Turbulent Core Accretion theory, are then fit to the SEDs to estimate key properties of the protostars. Considering the best five models fit to each source, the protostars have masses m _* ̃ 12-64 M _☉ accreting at rates of {\dot{m } }_* ̃ {10}^-4{--}{10}^-3 {M}_☉ {yr } }^-1 inside cores of initial masses {M}_c̃ 100{--}500 {M}_☉ embedded in clumps with mass surface densities { { {Σ } } }_cl}̃ 0.1{--}3 { { g } } {cm } }^-2 and span a luminosity range of 10⁴-10⁶ L _☉. Compared with the first eight protostars in Paper I, the sources analyzed here are more luminous and, thus, likely to be more massive protostars. They are often in a clustered environment or have a companion protostar relatively nearby. From the range of parameter space of the models, we do not see any evidence that Σ_cl needs to be high to form these massive stars. For most sources, the RT models provide reasonable fits to the SEDs, though the cold clump material often influences the long wavelength fitting. However, for sources in very clustered environments, the model SEDs may not be such a good description of the data, indicating potential limitations of the models for these regions....

DOI： 10.3847/1538-4357/ab07b7

arXiv

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

Almost all massive stars have bound stellar companions, existing in binaries or higher-order multiples^1-5. While binarity is theorized to be an essential feature of how massive stars form⁶, essentially all information about such properties is derived from observations of already formed stars, whose orbital properties may have evolved since birth. Little is known about binarity during formation stages. Here we report high-angular-resolution observations of 1.3 mm continuum and H30α recombination line emission, which reveal a massive protobinary with apparent separation of 180 au at the centre of the massive star-forming region IRAS 07299-1651. From the line-of-sight velocity difference of 9.5 km s^-1 of the two protostars, the binary is estimated to have a minimum total mass of 18 solar masses, consistent with several other metrics, and maximum period of 570 yr, assuming a circular orbit. The H30α line from the primary protostar shows kinematics consistent with rotation along a ring of radius of 12 au. The observations indicate that disk fragmentation at several hundred astronomical units may have formed the binary, and much smaller disks are feeding the individual protostars....

DOI： 10.1038/s41550-019-0718-y

arXiv

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Publishing type：Research paper (scientific journal)  

We report molecular line observations of the massive protostellar source G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The observations reveal a highly collimated SiO jet extending from the 1.3 mm continuum source, which connects to a slightly wider but still highly collimated CO outflow. Rotational features perpendicular to the outflow axis are detected in various molecular emissions, including SiO, SO₂, H₂S, CH₃OH, and H₂CO emissions. Based on their spatial distributions and kinematics, we find that they trace different parts of the envelope-disk system. The SiO emission traces the disk and inner envelope in addition to the jet. The CH₃OH and H₂CO emissions mostly trace the infalling-rotating envelope and are enhanced around the transition region between envelope and disk, i.e., the centrifugal barrier. The SO₂ and H₂S emissions are enhanced around the centrifugal barrier and also trace the outer part of the disk. Envelope kinematics are consistent with rotating-infalling motion, while those of the disk are consistent with Keplerian rotation. The radius and velocity of the centrifugal barrier are estimated to be about 530 au and 6 {km} { { {s } } }^-1, respectively, leading to a central mass of about 11 M _☉, consistent with estimates based on spectral energy distribution fitting. These results indicate that an ordered transition from an infalling-rotating envelope to a Keplerian disk through a centrifugal barrier, accompanied by changes of types of molecular line emissions, is a valid description of this massive protostellar source. This implies that at least some massive stars form in a similar way to low-mass stars via core accretion....

DOI： 10.3847/1538-4357/ab0553

arXiv

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Publishing type：Research paper (scientific journal)  

We study centimeter continuum emission of eight high- and intermediate-mass protostars that are part of the SOFIA Massive Star Formation Survey, thus building extended spectral energy distributions (SEDs) from the radio to the infrared. We discuss the morphology seen in the centimeter continuum images, which are mostly derived from archival Very Large Array data, and the relation to infrared morphology. We use the SEDs to test new models of high-mass star formation including radiative and disk-wind feedback and associated free-free and dust continuum emission. We show that interferometric data of the centimeter continuum flux densities provide additional, stringent tests of the models by constraining the ionizing luminosity of the source; they also help to break degeneracies encountered when modeling the infrared-only SEDs, especially for the protostellar mass. Our derived parameters are consistent with physical parameters estimated by other methods, such as dynamical protostellar masses. We find a few examples of additional stellar sources in the vicinity of the high-mass protostars, which may be low-mass young stellar objects. However, the stellar multiplicity of the regions, at least as traced by radio continuum emission, appears to be relatively low....

DOI： 10.3847/1538-4357/ab0209

arXiv

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Publisher：arXiv e-prints  

We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the outflow-core interaction for a massive protostar forming via collapse of an initial cloud core of $60~{M_\odot}$. This allows us to characterize the properties of disk wind driven outflows from massive protostars, which can allow testing of different massive star formation theories. It also enables us to assess quantitatively the impact of outflow feedback on protostellar core morphology and overall star formation efficiency. We find that the opening angle of the flow increases with increasing protostellar mass, in agreement with a simple semi-analytic model. Once the protostar reaches $\sim24~{M_\odot}$ the outflow's opening angle is so wide that it has blown away most of the envelope, thereby nearly ending its own accretion. We thus find an overall star formation efficiency of $\sim50\%$, similar to that expected from low-mass protostellar cores. Our simulation results therefore indicate that the MHD disk wind outflow is the dominant feedback mechanism for helping to shape the stellar initial mass function from a given prestellar core mass function....

arXiv

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Publishing type：Research paper (scientific journal)  

DOI： 10.1017/S1743921318005549

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Publishing type：Research paper (scientific journal)  

We conduct a theoretical study of the formation of massive stars over a wide range of metallicities from 10^-5 to 1 {Z}_☉ and evaluate the star formation efficiencies (SFEs) from prestellar cloud cores taking into account multiple feedback processes. Unlike for simple spherical accretion, feedback processes in the case of disk accretion do not set upper limits on stellar masses. At solar metallicity, launching of magneto-centrifugally driven outflows is the dominant feedback process to set SFEs, while radiation pressure, which has been regarded as pivotal, makes only a minor contribution even in the formation of stars over 100 {M}_☉ . Photoevaporation becomes significant in the formation of stars over 20 {M}_☉ at low metallicities of ≲ {10}^-2 {Z}_☉ , where dust absorption of ionizing photons is inefficient. We conclude that if initial prestellar core properties are similar, then massive stars are rarer in extremely metal-poor environments of 10^-5-{10}^-3 {Z}_☉ . Our results give new insight into the high-mass end of the initial mass function and its potential variation with galactic and cosmological environments....

DOI： 10.3847/1538-4357/aac892

arXiv

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Language：Japanese  

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

We present calculations of molecular, atomic, and ionic line emission from simulations of giant molecular cloud (GMC) collisions. We post-process snapshots of the magnetohydrodynamical simulations presented in an earlier paper in this series by Wu et al. of colliding and non-colliding GMCs. Using photodissociation region (PDR) chemistry and radiative transfer, we calculate the level populations and emission properties of the transitions of ¹²CO J = 1-0, [C I] {}³{ { {P } } }₁\to {}³{ { {P } } }₀ at 609 μm, [C II] 158 μm, and [O I] {}³{ { {P } } }₁\to {}³{ { {P } } }₀ at 63 μm. From emission maps of integrated intensity and position-velocity diagrams, we find that fine-structure lines, particularly [C II] 158 μm, can be used as a diagnostic tracer for cloud-cloud collision activity. These results hold even in more evolved systems in which the collision signature in molecular lines has been diminished....

DOI： 10.3847/1538-4357/aa94c5

arXiv

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

In this series of papers, we model the formation and evolution of the photoionized region and its observational signatures during massive star formation. Here, we focus on the early breakout of the photoionized region into the outflow cavity. Using results of 3D magnetohydrodynamic-outflow simulations and protostellar evolution calculations, we perform a post-processing radiative transfer. The photoionized region first appears at a protostellar mass of {m}_* =10 {M}_☉ in our fiducial model and is confined to within 10-100 au by the dense inner outflow, which is similar to some of the observed very small hypercompact H II regions. Since the ionizing luminosity of the massive protostar increases dramatically as the Kelvin-Helmholtz (KH) contraction proceeds, the photoionized region breaks out to the entire outflow region in ≲10,000 year. Accordingly, the radio free-free emission brightens significantly in this stage. In our fiducial model, the radio luminosity at 10 GHz changes from 0.1 {mJy} { { kpc } }² at {m}_* =11 {M}_☉ to 100 {mJy} { { kpc } }² at {m}_* =16 {M}_☉ , while the infrared luminosity increases by less than a factor of two. The radio spectral index also changes in the break-out phase from the optically thick value of ̃2 to the partially optically thin value of ̃0.6. Additionally, we demonstrate that short-timescale variation in the free-free flux would be induced by an accretion burst. The outflow density is enhanced in the accretion burst phase, which leads to a smaller ionized region and weaker free-free emission. The radio luminosity may decrease by one order of magnitude during such bursts, while the infrared luminosity is much less affected because internal protostellar luminosity dominates over accretion luminosity after the KH contraction starts. Such a variability may be observable on timescales as short 10-100 year if accretion bursts are driven by disk instabilities....

DOI： 10.3847/1538-4357/aa9076

arXiv

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Publishing type：Research paper (scientific journal)  

We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ̃10 to 40 μm. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid-infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m_* ̃ 10-50 M_☉ accreting at ̃10^-4-10^-3 M_☉ yr^-1 inside cores of initial masses M_c ̃ 30-500 M_☉ embedded in clumps with mass surface densities Σ_cl ̃ 0.1-3 g cm^-2. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ̃100× smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories....

DOI： 10.3847/1538-4357/aa74c8

arXiv

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

We study feedback during massive star formation using semi-analytic methods, considering the effects of disk winds, radiation pressure, photoevaporation, and stellar winds, while following protostellar evolution in collapsing massive gas cores. We find that disk winds are the dominant feedback mechanism setting star formation efficiencies (SFEs) from initial cores of ̃0.3-0.5. However, radiation pressure is also significant to widen the outflow cavity causing reductions of SFE compared to the disk-wind only case, especially for &gt; 100 {M}_☉ star formation at clump mass surface densities { { {Σ } } }_{cl}≲ 0.3 { { g } } { { cm } }^-2. Photoevaporation is of relatively minor importance due to dust attenuation of ionizing photons. Stellar winds have even smaller effects during the accretion stage. For core masses {M}_c≃ 10-1000 {M}_☉ and { { {Σ } } }_{cl}≃ 0.1-3 { { g } } { { cm } }^-2, we find the overall SFE to be {\bar{\varepsilon } }_{* f}=0.31{({R}_c/0.1{pc})}^-0.39, potentially a useful sub-grid star formation model in simulations that can resolve pre-stellar core radii, {R}_c=0.057{({M}_c/60{M}_☉ )}^1/2{({ { {Σ } } }_{cl}/{ { g } }{ { cm } }^-2)}^-1/2 {pc}. The decline of SFE with M _c is gradual with no evidence for a maximum stellar-mass set by feedback processes up to stellar masses of {m}_* ̃ 300 {M}_☉ . We thus conclude that the observed truncation of the high-mass end of the IMF is shaped mostly by the pre-stellar core mass function or internal stellar processes. To form massive stars with the observed maximum masses of ̃150-300{M}_☉ , initial core masses need to be ≳ 500-1000 {M}_☉ . We also apply our feedback model to zero-metallicity primordial star formation, showing that, in the absence of dust, photoevaporation staunches accretion at ̃ 50 {M}_☉ . Our model implies radiative feedback is most significant at metallicities ̃ {10}^-2{Z}_☉ , since both radiation pressure and photoevaporation are effective in this regime....

DOI： 10.3847/1538-4357/835/1/32

arXiv

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

DOI： 10.1017/S1743921317011516

Scopus

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

We present an evolutionary sequence of models of the photoionized disk-wind outflow around forming massive stars based on the Core Accretion model. The outflow is expected to be the first structure to be ionized by the protostar and can confine the expansion of the H II region, especially in lateral directions in the plane of the accretion disk. The ionizing luminosity increases as Kelvin-Helmholz contraction proceeds, and the H II region is formed when the stellar mass reaches ̃10-20{M}_☉ depending on the initial cloud core properties. Although some part of the outer disk surface remains neutral due to shielding by the inner disk and the disk wind, almost the whole of the outflow is ionized in 10³-{10}⁴ { { y } }{ { r } } after initial H II region formation. Having calculated the extent and temperature structure of the H II region within the immediate protostellar environment, we then make predictions for the strength of its free-free continuum and recombination line emission. The free-free radio emission from the ionized outflow has a flux density of ̃(20-200) × \quad {(ν /10{ { GHz } })}^p { { mJy } } for a source at a distance of 1 kpc with a spectral index p ≃ 0.4-0.7, and the apparent size is typically ̃500 AU at 10 GHz. The { { H } }40α line profile has a width of about 100 {km} { { {s } } }^-1. These properties of our model are consistent with observed radio winds and jets around forming massive protostars....

DOI： 10.3847/0004-637X/818/1/52

arXiv

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Publishing type：Research paper (scientific journal)  

We have initiated single-dish monitoring observations of ~400 methanol maser sources at 6.7 GHz using the Hitachi 32-m radio telescope from December 2012 to systematically research periodic flux variations, which are observed in some methanol maser sources associated with high-mass (proto-)stars. In our monitoring, we have made daily monitoring, so that each source has been observed every nine days with an integration time of 5 min (typical detection sensitivities of 0.9 Jy). The monitoring observations help us statistically understand periodic flux variations with a period longer than 50 days. As an initial result, we present a new detection of periodic flux variations in the 6.7 GHz methanol maser source G036.70+00.09. The period of the flux variations is ~53 days (~0.019 cycles), and seems to be stable over 9 cycles, at least until the middle of August 2014....

DOI： 10.5303/PKAS.2015.30.2.129

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Publishing type：Research paper (scientific journal)  

Fragmentation of protostellar discs controls the growth of protostars and plays a key role in determining the final mass of newborn stars. In this paper, we investigate the structure and gravitational stability of the protostellar discs in the full metallicity range between zero and the solar value. Using the mass-accretion rates evaluated from the thermal evolution in the preceding collapse phase of the pre-stellar cores, we calculate disc structures and their evolution in the framework of the standard steady discs. Overall, with higher metallicity, more efficient cooling results in the lower accretion rate and lower temperature inside the disc: at zero metallicity, the accretion rate is ̃10^-3 M_☉ yr^-1 and the disc temperature is ̃1000 K, while at solar metallicity, ̃10^-6 M_☉ yr^-1 and ̃10 K. Despite the large difference in these values, the zero- and solar-metallicity discs have similar stability properties: the Toomre parameter for the gravitational stability, which can be written using the ratio of temperatures in the disc and in the envelope as Q_T ̃ (T_disc/T_env)^3/2, is ≳ 1, i.e. marginally stable. At intermediate metallicities of 10^-5 to 10^-3 Z_☉, however, the discs are found to be strongly unstable with Q_T ̃ 0.1-1 since dust cooling, which is effective only in the discs due to their high density ( ≳ 10¹⁰ cm^{- 3}), makes the temperature in the discs lower than that in the envelopes. This indicates that masses of the individual stars formed as a result of the protostellar disc fragmentation can be significantly smaller than their parent core in this metallicity range. The typical stellar mass in this case would be a few M_☉, which is consistent with the observationally suggested mass-scale of extremely metal-poor stars....

DOI： 10.1093/mnras/stu069

arXiv

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Publishing type：Research paper (scientific journal)  

Photoevaporation by stellar ionizing radiation is believed to play an important role in the dispersal of disks around young stars. The mass-loss model for dust-free disks developed by Hollenbach et al. is currently regarded as the conventional one and has been used in a wide variety of studies. However, the rate in this model was derived using the crude so-called 1+1D approximation of ionizing radiation transfer, which assumes that diffuse radiation propagates in a direction vertical to the disk. In this study, we revisit the photoevaporation of dust-free disks by solving the two-dimensional axisymmetric radiative transfer for steady-state disks. Unlike that solved by the conventional model, we determine that direct stellar radiation is more important than the diffuse field at the disk surface. The radial density distribution at the ionization boundary is represented by a single power law with index -3/2 in contrast to the conventional double power law. For this distribution, the photoevaporation rate from the entire disk can be written as a function of the ionizing photon emissivity Φ_EUV from the central star and the disk outer radius r _d as follows: \dot{M}_PE = 5.4 \times 10^{-5} (\Phi _EUV/10^{49}\ s^{-1})^{1/2} (r_d/1000\ AU)^{1/2} \ M_\odot \ yr^{-1}. This new rate depends on the outer disk radius rather than on the gravitational radius as in the conventional model, because of the enhanced contribution to the mass loss from the outer disk annuli. In addition, we discuss its applications to present-day as well as primordial star formation....

DOI： 10.1088/0004-637X/773/2/155

arXiv

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Publishing type：Research paper (scientific journal)  

The 6.7 GHz methanol maser emission, a tracer of forming massive stars, sometimes shows enigmatic periodic flux variations over several 10-100 days. In this Letter, we propose that these periodic variations could be explained by the pulsation of massive protostars growing under rapid mass accretion with rates of \,\dot{M}_{\ast }\gtrsim 10^{-3} \,{M}_{\odot }\, yr^{-1}. Our stellar evolution calculations predict that the massive protostars have very large radii exceeding 100 R _☉ at maximum, and here we study the pulsational stability of such bloated protostars by way of the linear stability analysis. We show that the protostar becomes pulsationally unstable with various periods of several 10-100 days depending on different accretion rates. With the fact that the stellar luminosity when the star is pulsationally unstable also depends on the accretion rate, we derive the period-luminosity relation log (L/ L _☉) = 4.62 + 0.98log (P/100 days), which is testable with future observations. Our models further show that the radius and mass of the pulsating massive protostar should also depend on the period. It would be possible to infer such protostellar properties and the accretion rate with the observed period. Measuring the maser periods enables a direct diagnosis of the structure of accreting massive protostars, which are deeply embedded in dense gas and are inaccessible with other observations....

DOI： 10.1088/2041-8205/769/2/L20

arXiv

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

DOI： 10.1063/1.4754409

Web of Science

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Publishing type：Research paper (scientific journal)  

In massive star formation (gsim 40 M _sun) by core accretion, the direct stellar radiation pressure acting on the dust particles exceeds the gravitational force and interferes with mass accretion at the dust sublimation front, the first absorption site. Ram pressure generated by high accretion rates of 10^-3 M _sun yr^-1 is thought to be required to overcome the direct stellar radiation pressure. We investigate the direct stellar irradiation on the dust sublimation front, including the inner accretion disk structure. We show that the ram pressure of the accretion disk is lower than the stellar radiation pressure at the dust sublimation front. Thus, another mechanism must overcome the direct stellar radiation pressure. We suggest that the inner hot dust-free region is optically thick, shielding the dust sublimation front from direct stellar irradiation. Thus, accretion would not halt at the dust sublimation front, even at lower accretion rates....

DOI： 10.1088/2041-8205/739/2/L50

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Publishing type：Research paper (scientific journal)  

During the formation of a massive star, strong radiation pressure from the central star acts on the dust sublimation front and tends to halt the accretion flow. To overcome this strong radiation pressure, it has been considered that a strong ram pressure produced by a high-mass accretion rate of 10^-3 M _sun yr^-1 or more is needed. We reinvestigated the necessary condition to overcome the radiation pressure and found a new mechanism for overcoming it. Accumulated mass in a stagnant flow near the dust sublimation front helps the mass accretion by its weight. This mechanism relaxes the condition for the massive star formation. We call this mechanism the "OMOSHI effect," where OMOSHI is an acronym for "One Mechanism for Overcoming Stellar High radiation pressure by weIght." Additionally, in Japanese, OMOSHI is a noun meaning a weight that is put on something to prevent it from moving. We investigate the generation of the OMOSHI effect using local one-dimensional radiation hydrodynamics simulations. The radiation pressure and the gravitational force are connected through the gas pressure, and to sum up, the radiation pressure is balanced or overcome by the gravitational force. We also discuss the global structure and temporal variation of the accretion flow....

DOI： 10.1088/0004-637X/714/1/309

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

Web of Science

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