arXiv subjects

Mengyao Liu

Publications and source records attributed to Mengyao Liu.

At least 19 recordsLinked to original sources

arXiv2026

Silicone Ethernet (SEth): a Nervous System for Robotic Touch

Fine-grained robotic touch sensing is essential for tasks such as robot-human interaction and the handling of hazardous materials. Yet, the sense of touch of robots is limited by the cost and complexity of routing cables to embedded sensors. This paper tackles this problem by contributing Silicone Ethernet (SEth), a wireless solution for touch sensing, communication and power transfer within a conductive silicone substrate. SEth~\emph{neurons} require no battery and deliver computation, communication, sensing and energy harvesting within a compact package. These neurons are placed into an undifferentiated conductive silicone substrate which may form the entire body of a soft robot, or an outer `skin' for hard robots. Our evaluation shows that SEth achieves data rates of 100\,kbps with sub-$μ$W receive and mW-scale transmit power. Exploiting the unique properties of the conductive silicone substrate, SEth provides prioritized traffic arbitration similar to that found in wired control networks such as CAN. The SEth network inherently supports capacitive touch and presence sensing and neurons can harvest sufficient energy to transmit 10s of messages per second at a range of 1\,m. Considered in sum, these features open new degrees of freedom in touch sensing for soft robots.

cs.NI↗

arXiv2025

The SOFIA Massive (SOMA) Star Formation Survey. V. Clustered Protostars

We present $\sim8-40\,μ$m SOFIA-FORCAST images of seven regions of ``clustered" star formation as part of the SOFIA Massive (SOMA) 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, $Σ_{\rm cl}$, and current protostellar mass, $m_*$. We also carry out empirical graybody (GB) estimation of $Σ_{\rm cl}$, 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 \emph{sedcreator}, 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 $M_c\sim30-200\:M_{\odot}$, $Σ_{\text{cl,SED}}\sim0.1-3\:{\rm{g\:cm}}^{-2}$, and $m_*\sim4-50\:M_{\odot}$. The graybody fitting yields smaller values of $Σ_{\text{cl,GB}}\lesssim1\:{\rm{g\:cm}}^{-2}$. From these results, we do not find evidence for a critical $Σ_{\rm{cl}}$ needed to form massive ($\gtrsim 8\:M_\odot$) stars. However, we do find tentative evidence for a dearth of the most massive ($m_*\gtrsim30\:M_\odot$) protostars in the clustered regions suggesting a potential impact of environment on the stellar initial mass function.

astro-ph.GA↗

arXiv2025

Symmetry and classification of positive solutions of some weighted elliptic equations

We study the weighted elliptic equation \begin{equation} -div(|x|^{-2a}\nabla u)=|x|^{-bp}|u|^{p-2}u~~~\mbox{in}~\mathbb{R}^N ~~~~~~~~~~~~~~~~~~~~(0.1)\end{equation} with $N\geq 2$, which arises from the Caffarelli-Kohn-Nirenberg inequalities. Under the assumptions of finite energy and $a_1+a_2=N-2$, for nonnegative solutions we prove the equivalence between equation (0.1) with $a=a_1$ and equation (0.1) with $a=a_2$. Without finite energy assumptions, for $2\leq p<2^*$ we give the optimal parameter range in which nonnegative solutions of (0.1) in $\mathbf{L}^\infty_{Loc}(\mathbb{R}^N)$ must be radially symmetric, and give a complete classification for these solutions in this range.

math.AP↗

arXiv2023

Surveying the Giant HII Regions of the Milky Way with SOFIA: V. DR7 and K3-50

We present our fifth set of results from our mid-infrared imaging survey of Milky Way Giant HII (GHII) regions with our detailed analysis of DR7 and K3-50. We obtained 20/25 and 37um imaging maps of both regions using the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). We investigate the multi-scale properties of DR7 and K3-50 using our data in conjunction with previous multi-wavelength observations. Near to far-infrared spectral energy distributions of individual compact infrared sources were constructed and fitted with massive young stellar object (MYSO) models. We find eight out of the ten (80%) compact sources in K3-50 and three out of the four (75%) sources in DR7 are likely to be MYSOs. We derived luminosity-to-mass ratios of the extended radio sub-regions of DR7 and K3-50 to estimate their relative ages. The large spread in evolutionary state for the sub-regions in K3-50 likely indicates that the star-forming complex has undergone multiple star-forming events separated more widely in time, whereas the smaller spread in DR7 likely indicates the star formation sub-regions are more co-eval. DR7 and K3-50 have Lyman continuum photon rates just above the formal threshold criterion for being categorized as a GHII region (10^50 photons/s) but with large enough errors that this classification is uncertain. By measuring other observational characteristics in the infrared, we find that K3-50 has properties more akin to previous bona fide GHII regions we have studied, whereas DR7 has values more like those of the non-GHII regions we have previously studied.

astro-ph.GA↗

arXiv2023

The SOFIA Massive (SOMA) Star Formation Survey. IV. Isolated Protostars

We present $\sim10-40\,μ$m SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 $μ$m 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 $20-430\:M_\odot$, clump mass surface densities $Σ_{\rm cl}\sim0.3-1.7\:{\rm{g\:cm}}^{-2}$ and current protostellar masses $m_*\sim3-50\:M_\odot$. 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 $Σ_{\rm cl}$ for massive star formation. However, the upper end of the $m_*-Σ_{\rm cl}$ distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher $Σ_{\rm cl}$ conditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an $\sim$40 year baseline.

astro-ph.GA↗

arXiv2021

Surveying the Giant HII Regions of the Milky Way with SOFIA: III. W49A

We present our third set of results from our mid-infrared imaging survey of Milky Way Giant HII (GHII) regions with our detailed analysis of W49A, one of the most distant, yet most luminous, GHII regions in the Galaxy. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to obtain 20 and 37$μ$m images of the entire ~5.0' x 3.5' infrared-emitting area of W49A at a spatial resolution of ~3". Utilizing these SOFIA data in conjunction with previous multi-wavelength observations from the near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archival data, we investigate the physical nature of individual infrared sources and sub-components within W49A. For individual compact sources we used the multi-wavelength photometry data to construct spectral energy distributions (SEDs) and fit them with massive young stellar object (MYSO) SED models, and find 22 sources that are likely to be MYSOs. Ten new sources are identified for the first time in this work. Even at 37$μ$m we are unable to detect infrared emission from the sources on the western side of the extremely extinguished ring of compact radio emission sources known as the Welch Ring. Utilizing multi-wavelength data, we derived luminosity-to-mass ratio and virial parameters of the extended radio sub-regions of W49A to estimate their relative ages and find that overall the sub-components of W49A have a very small spread in evolutionary state compared to our previously studied GHII regions.

astro-ph.GA↗

arXiv2021

SiO Outflows as Tracers of Massive Star Formation in Infrared Dark Clouds

To study the early phases of massive star formation, we present ALMA observations of SiO(5-4) emission and VLA observations of 6 cm continuum emission towards 32 Infrared Dark Cloud (IRDC) clumps, spatially resolved down to $\lesssim 0.05$ pc. Out of the 32 clumps, we detect SiO emission in 20 clumps, and in 11 of them the SiO emission is relatively strong and likely tracing protostellar outflows. Some SiO outflows are collimated, while others are less ordered. For the six strongest SiO outflows, we estimate basic outflow properties. In our entire sample, where there is SiO emission, we find 1.3 mm continuum and infrared emission nearby, but not vice versa. We build the spectral energy distributions (SEDs) of cores with 1.3 mm continuum emission and fit them with radiative transfer (RT) models. The low luminosities and stellar masses returned by SED fitting suggest these are early stage protostars. We see a slight trend of increasing SiO line luminosity with bolometric luminosity, which suggests more powerful shocks in the vicinity of more massive YSOs. We do not see a clear relation between the SiO luminosity and the evolutionary stage indicated by $L/M$. We conclude that as a protostar approaches a bolometric luminosity of $\sim 10^2 \: L_{\odot}$, the shocks in the outflow are generally strong enough to form SiO emission. The VLA 6 cm observations toward the 15 clumps with the strongest SiO emission detect emission in four clumps, which is likely shock ionized jets associated with the more massive ones of these protostellar cores.

astro-ph.GA↗

arXiv2021

Star Formation in a Strongly Magnetized Cloud

We study star formation in the Center Ridge 1 (CR1) clump in the Vela C giant molecular cloud, selected as a high column density region that shows the lowest level of dust continuum polarization angle dispersion, likely indicating that the magnetic field is relatively strong. We observe the source with the ALMA 7m-array at 1.05~mm and 1.3~mm wavelengths, which enable measurements of dust temperature, core mass and astrochemical deuteration. A relatively modest number of eleven dense cores are identified via their dust continuum emission, with masses spanning from 0.17 to 6.7 Msun. Overall CR1 has a relatively low compact dense gas fraction compared with other typical clouds with similar column densities, which may be a result of the strong magnetic field and/or the very early evolutionary stage of this region. The deuteration ratios, Dfrac, of the cores, measured with N2H+(3-2) and N2D+(3-2) lines, span from 0.011 to 0.85, with the latter being one of the highest values yet detected. The level of deuteration appears to decrease with evolution from prestellar to protostellar phase. A linear filament, running approximately parallel with the large scale magnetic field orientation, is seen connecting the two most massive cores, each having CO bipolar outflows aligned orthogonally to the filament. The filament contains the most deuterated core, likely to be prestellar and located midway between the protostars. The observations permit measurement of the full deuteration structure of the filament along its length, which we present. We also discuss the kinematics and dynamics of this structure, as well as of the dense core population.

astro-ph.GA↗

arXiv2021

The Core Mass Function Across Galactic Environments. III. Massive Protoclusters

The stellar initial mass function (IMF) is fundamental for many areas of astrophysics, but its origin remains poorly understood. It may be inherited from the core mass function (CMF) or arise as a result of more chaotic, competitive accretion. Dense, gravitationally bound cores are seen in molecular clouds and some observations have suggested that the CMF is similar in shape to the IMF, though translated to higher masses by a factor of $\sim3$. Here we measure the CMF in 28 dense clumps within 3.5 kpc that are likely to be central regions of massive protoclusters, observed via $1.3\:{\rm{mm}}$ dust continuum emission by the ALMAGAL project. We identify 222 cores using the dendrogram algorithm with masses ranging from 0.04 to $252\:M_{\odot}$. We apply completeness corrections for flux and number recovery, estimated from core insertion and recovery experiments. At higher masses, the final derived CMF is well described by a single power law of the form $dN/d\:{\textrm{log}}\:M\propto\:M^{-α}$ with $α\simeq0.94\pm0.08$. However, we find evidence of a break in this power-law behavior between $\sim5$ and $15\:M_{\odot}$, which is, to our knowledge, the first time such a break has been found in distant ($\gtrsim 1$ kpc) regions by ALMA. We compare this massive protocluster CMF with those derived using the same methods in the G286 protocluster and a sample of Infrared Dark Clouds. The massive protocluster CMF is significantly different, i.e., containing more massive cores, which is a potential indication of the role of environment on the CMF and IMF.

astro-ph.GA↗

arXiv2020

The SOFIA Massive (SOMA) Star Formation Survey. III. From Intermediate- to High-Mass Protostars

We present $\sim10-40\,μ$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 (SEDs), also utilizing archival Spitzer, Herschel and IRAS data. We then fit the SEDs with radiative transfer (RT) models of Zhang & Tan (2018), based on Turbulent Core Accretion theory, to estimate key protostellar properties. With the addition of these intermediate-mass sources, SOMA protostars span luminosities from $\sim10^{2}-10^{6}\:L_{\odot}$, current protostellar masses from $\sim0.5-30\:M_{\odot}$ and ambient clump mass surface densities, $Σ_{\rm cl}$ from $0.1-3\:{\rm{g\:cm}^{-2}}$. A wide range of evolutionary states of the individual protostars and of the protocluster environments are also probed. We have also considered about 50 protostars identified in 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, there is no evidence of a threshold value of protocluster clump mass surface density being needed to form protostars up to $\sim25\:M_\odot$. However, to form more massive protostars, there is tentative evidence that $Σ_{\rm{cl}}$ needs to be $\gtrsim1\:{\rm{g\,cm}}^{-2}$. We discuss how this is consistent with expectations from core accretion models that include internal feedback from the forming massive star.

astro-ph.GA↗

arXiv2020

Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks

We report results of 0.05"-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array (ALMA). 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 Eu/k>3000K, 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 interpret 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 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.

astro-ph.SR↗

arXiv2020

The High-Mass Protostellar Population of a Massive Infrared Dark Cloud

We conduct a census of the high-mass protostellar population of the $\sim70,000\:M_\odot$ Infrared Dark Cloud (IRDC) G028.37+00.07, identifying 35 sources based on their $70\:μ$m emission, as reported in the {\it Herschel} Hi-GAL catalog of Molinari et al. (2016). We perform aperture photometry to construct spectral energy distributions (SEDs), which are then fit with the massive protostar models of Zhang & Tan (2018). We find that the sources span a range of isotropic luminosities from $\sim$20 to 4,500$\:L_\odot$. The most luminous sources are predicted to have current protostellar masses of $m_{*}\sim10\:M_\odot$ forming from cores of mass $M_{c}\sim40$ to $400\:M_\odot$. The least luminous sources in our sample are predicted to be protostars with masses as low as $\sim 0.5\:M_\odot$ forming from cores with $M_{c}\sim10\:M_\odot$, which are the minimum values explored in the protostellar model grid. The detected protostellar population has a total estimated protostellar mass of $M_{*}\sim 100\:M_\odot$. Allowing for completeness corrections, which are constrained by comparison with an ALMA study in part of the cloud, we estimate a star formation efficiency per free-fall time of $\sim3\%$ in the IRDC. Finally, analyzing the spatial distribution of the sources, we find relatively low degrees of central concentration of the protostars. The protostars, including the most massive ones, do not appear to be especially centrally concentrated in the protocluster as defined by the IRDC boundary.

astro-ph.GA↗

arXiv2020

Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA

We study the gas kinematics and dynamics of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array using spectral lines of $C^{18}O$(2-1), $N_2D^+$(3-2), $DCO^+$(3-2) and $DCN$(3-2). On the parsec clump scale, $C^{18}O$ emission appears highly filamentary around the systemic velocity. $N_2D^+$ and $DCO^+$ are more closely associated with the dust continuum. $DCN$ is strongly concentrated towards the protocluster center, where no or only weak detection is seen for $N_2D^+$ and $DCO^+$, possibly due to this region being at a relatively evolved evolutionary stage. Spectra of 76 continuum defined dense cores, typically a few 1000 AU in size, are analysed to measure their centroid velocities and internal velocity dispersions. There are no statistically significant velocity offsets of the cores among the different dense gas tracers. Furthermore, the majority (71\%) of the dense cores have subthermal velocity offsets with respect to their surrounding, lower density $C^{18}O$ emitting gas. Within the uncertainties, the dense cores in G286 show internal kinematics that are consistent with being in virial equilibrium. On clumps scales, the core to core velocity dispersion is also similar to that required for virial equilibrium in the protocluster potential. However, the distribution in velocity of the cores is largely composed of two spatially distinct groups, which indicates that the dense molecular gas has not yet relaxed to virial equilibrium, perhaps due to there being recent/continuous infall into the system.

astro-ph.GA↗

arXiv2019

Aff-Wild Database and AffWildNet

In the context of HCI, building an automatic system to recognize affect of human facial expression in real-world condition is very crucial to make machine interact naturallisticaly with a man. However, existing facial emotion databases usually contain expression in the limited scenario under well-controlled condition. Aff-Wild is currently the largest database consisting of spontaneous facial expression in the wild annotated with valence and arousal. The first contribution of this project is the completion of extending Aff-Wild database which is fulfilled by collecting videos from YouTube on which the videos have spontaneous facial expressions in the wild, annotating videos with valence and arousal ranging in [-1,1], detecting faces in frames using FFLD2 detector and partitioning the whole data set into train, validate and test set, with 527056, 94223 and 135145 frames. The diversity is guaranteed regarding age, ethnicity and values of valence and arousal. The ratio of male to female is close to 1. Regarding the techniques used to build the automatic system, deep learning is outstanding since almost all winning methods in emotion challenges adopt DNN techniques. The second contribution of this project is that an end-to-end DNN is constructed to have joint CNN and RNN block and gives the estimation on valence and arousal for each frame in sequential data. VGGFace, ResNet, DenseNet with the corresponding pre-trained model for CNN block and LSTM, GRU, IndRNN, Attention mechanism for RNN block are experimented aiming to find the best combination. Fine tuning and transfer learning techniques are also tried out. By comparing the CCC evaluation value on test data, the best model is found to be pre-trained VGGFace connected with 2 layers GRU with attention mechanism. The models test performance is 0.555 CCC for valence with sequence length 80 and 0.499 CCC for arousal with sequence length 70.

cs.LG↗

arXiv2019

Discovery of a Photoionized Bipolar Outflow towards the Massive Protostar G45.47+0.05

Massive protostars generate strong radiation feedback, which may help set the mass 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 towards 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 ~1.5x10^7 cm^-3 at the center, launched from a disk of radius of 110 au. H30alpha 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 Msun based on the derived ionizing photon rate, or 30-40 Msun based on the H30alpha 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)x10^-5 Msun/yr. We also found hints of a possible jet embedded inside the wide-angle ionized outflow with non-thermal emissions. The possible co-existence of a jet and a massive photoevaporation outflow suggests that, in spite of the strong photoionization feedback, accretion is still on-going.

astro-ph.SR↗

arXiv2019

Dynamics of a Massive Binary at Birth

Almost all massive stars have bound stellar companions, existing in binaries or higher-order multiples. While binarity is theorized to be an essential feature of how massive stars form, 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 H30alpha recombination line emission, which reveal a massive protobinary with apparent separation of 180 au at the center of the massive star-forming region IRAS07299-1651. From the line-of-sight velocity difference of 9.5 km/s 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 years, assuming a circular orbit. The H30alpha 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 au may have formed the binary, and much smaller disks are feeding the individual protostars.

astro-ph.SR↗

arXiv2019

The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars

We present multi-wavelength images observed with SOFIA-FORCAST from $\sim$10 to 40 $μ$m of seven high luminosity massive protostars, as part of the SOFIA Massive (SOMA) 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 & Tan (2018), 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 $m_{*} \sim 12-64 \: M_{\odot}$ accreting at rates of $\dot{m}_{*} \sim 10^{-4}-10^{-3} \: M_{\odot} \: \rm yr^{-1}$ inside cores of initial masses $M_{c} \sim 100-500 \: M_{\odot}$ embedded in clumps with mass surface densities $Σ_{\rm cl} \sim 0.1-3 \: \rm g \: cm^{-2}$ and span a luminosity range of $10^{4} -10^{6} \: L_{\odot}$. 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 $Σ_{\rm cl}$ 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.

astro-ph.GA↗

arXiv2019

An Ordered Envelope-disk Transition in the Massive Protostellar Source G339.88-1.26

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, leading to a central mass of about 11 solar masses, 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 as low-mass stars via Core Accretion.

astro-ph.GA↗