arXiv subjects

I. I. Zinchenko

Publications and source records attributed to I. I. Zinchenko.

At least 19 recordsLinked to original sources

arXiv2026

Southern eROSITA bubble as a forward shock and the low-metallicity CGM. South-east side story

Unlike the complicated X-ray and radio structure observed in the North Polar Spur area, the South-Eastern part of the eROSITA bubbles can be reasonably well described as a propagating forward shock, plausibly created by the transient energy release at the Galactic Center. In this model, the physical radius of the bubble is $R_{\rm b}\sim 7-8\,{\rm kpc}$ and the age of the outburst is $t_{\rm age}\sim 5-8\,{\rm Myr}$. The latter quantity is plausibly a lower limit on the true age. The visible segment of the shock front (located at a distance of $\sim 10-12\,{\rm kpc}$ above the Galactic Disk and at a similar distance from the Sun) is currently expanding with the velocity $\sim 700\,{\rm km\,s^{-1}}$ through the gas with density $n_e\sim 3\times 10^{-4}\,{\rm cm^{-3}}$, and the abundance of heavy elements in this gas is low $Z\sim 0.1-0.2 \times Z_\odot$ (depending on the adopted reference Solar abundances). Unlike constraints derived from the line-of-sight-integrated quantities, these are effectively in situ measurements of the circumgalactic medium (CGM) properties. Given the simplifying assumptions used in deriving the density and abundance, we assign a factor of 2 systematic uncertainty to the final estimates. An eventual decisive test for the shock properties can be provided by the velocity measurements of the X-ray-emitting gas with soft X-ray bolometers. The extended forward shock propagating through low-metallicity gas is a favorable site to accelerate very high-energy cosmic rays, which might contribute to the recently discovered proton-rich Galactic cosmic ray component at PeV energies impinging on the Earth's atmosphere.

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arXiv2026

Unveiling an Hourglass-Shaped Magnetic Field toward IRDC G351.77-0.53

We present the SOFIA/HAWC+ 214 $μ$m polarimetric observations toward the infrared dark cloud G351.77-0.53 (hereafter G351), complemented by existing multi-wavelength data sets. Infrared excess from the embedded sources indicate ongoing star formation activity in the cloud. The G351 cloud hosts two prominent star-forming clumps, i.e., c1 and c2. The plane-of-the-sky magnetic field lines from Planck observations are predominantly oriented perpendicular to the filament's major axis. Magnetic field orientations from SOFIA/HAWC+ 214 $μ$m observations reveal distinct hourglass-shaped field configuration toward c1, while the field lines remain perpendicular to the rest of the filament. Using the Davis-Chandrasekhar-Fermi method, we estimate a mean plane-of-the-sky magnetic field strength of $\sim$147 $\pm$ 60 $μ$G in the G351 filament, with values reaching $\sim$0.8 mG toward c1. The mass-to-flux ratio analysis indicates that the filament is magnetically transcritical, where the gravitational and magnetic field energies are comparable. The hourglass-shaped magnetic field observed toward c1 could result from magnetically regulated gravitational collapse, the alignment of converging sub-filaments with the magnetic field, or a combination of both processes. The energy budget analysis further indicates that magnetic fields play an important role in governing the cloud's gas dynamics, followed by contributions from turbulence and gravity.

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arXiv2025

Submillimeter Class II methanol masers near the massive protostar S255IR NIRS3: evolution and excitation of the $J_1 -J_0$ A$^{-+}$ series and a new maser line at 345.919 GHz

We present the results of the further investigation of the Class II methanol maser emission in the $14_1 - 14_0$ A$^{-+}$ transition at 349.1 GHz discovered in 2016 in the remarkable core S255IR-SMA1, harboring a $\sim$20 M$_\odot$ protostar NIRS3, which exhibited a disk-mediated accretion burst in 2015. The present study is based on the observations of this object with ALMA in Band 7 at the largest baselines, which provide the angular resolution of $\sim$15 mas. We estimated physical conditions in the region from which comes the maser emission, and in the surroundings, using the presumably quasi-thermal methanol lines in our bands and the CH$_3$CN $19_\mathrm{K} - 18_\mathrm{K}$ line series. The total flux density in the $14_1 - 14_0$ A$^{-+}$ line in 2021 is about two times higher than in 2019. A maser emission of about the same intensity in 2021 is detected for the first time in the $12_1 - 12_0$ A$^{-+}$ transition at 336.9 GHz. The physical conditions in the masering and non-masering regions are similar. The masers are apparently excited by the radiation of the central source. Unfortunately, the existing models cannot adequately take into account this radiation. The $18_{-3}-17_{-4}$ E transition at 345.919 GHz shows characteristics of maser emission, too.

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arXiv2024

Study of the physical and chemical properties of dense clumps at different evolutionary stages in several regions of massive star and stellar cluster formation

Massive stars play an important role in the Universe. Unlike low-mass stars, the formation of these objects located at great distances is still unclear. It is expected to be governed by some combination of self-gravity, turbulence, and magnetic fields. In this work, we aim to study the chemical and physical conditions of dense clumps at different evolutionary stages. We performed observations towards 5 regions of massive star and stellar cluster formation (L1287, S187, S231, DR 21(OH), NGC 7538) with the IRAM-30m telescope. We covered the 2 and 3$-$4 mm wavelength bands and analysed the lines of HCN, HNC, HCO$^+$, HC$_3$N, HNCO, OCS, CS, SiO, SO$_2$, and SO. Using astrodendro algorithm on the 850 $μ$m dust emission data from the SCUBA Legacy catalogue, we determined the masses, H$_2$ column densities, and sizes of the clumps. Furthermore, the kinetic temperatures, molecular abundances, and dynamical state were obtained. The Red Midcourse Space Experiment Source survey (RMS) was used to determine the clump types. A total of 20 clumps were identified. Three clumps were found to be associated with the Hii regions, 10 with young stellar objects (YSOs), and 7 with submillimetre emission. The clumps have typical sizes of about 0.2 pc and masses ranging from 1 to $10^{2}\,M_\odot$, kinetic temperatures ranging from 20 to 40 K and line widths of $\rm H^{13}CO^{+} (1-0)$ approximately 2 $\rm km\,s^{-1}$. We found no significant correlation in the line width$-$size and the line width$-$mass relationships. However, a strong correlation is observed in mass$-$size relationships. The virial analysis indicated that three clumps are gravitationally bound. Furthermore, we suggested that magnetic fields of about 1 mG provide additional support for clump stability. The molecular abundances relative to H$_2$ are approximately $10^{-10}-10^{-8}$.

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arXiv2024

North Polar Spur: gaseous plume(s) from star-forming regions at $\sim$3-5 kpc from Galactic Center?

We argue that the North Polar Spur (NPS) and many less prominent structures are formed by gaseous metal-rich plumes associated with star-forming regions (SFRs). The SFRs located at the tangent to the 3-5~kpc rings might be particularly relevant to NPS. A multi-temperature mixture of gaseous components and cosmic rays rises above the Galactic disk under the action of their initial momentum and buoyancy. Eventually, the plume velocity becomes equal to that of the ambient gas, which rotates with different angular speed than the stars in the disk. As a result, the plumes acquire characteristic bent shapes. An ad hoc model of plumes' trajectories shows an interesting resemblance to the morphology of structures seen in the radio continuum and X-rays.

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arXiv2024

Fine structure and kinematics of the ionized and molecular gas in the jet and disk around S255IR NIRS3 from high resolution ALMA observations

We present observations of the high-mass star-forming region S255IR, which harbors the $\sim$20 M$_\odot$ protostar NIRS3, where a disk-mediated accretion burst was recorded several years ago, with the angular resolution of $\sim$15 mas, which corresponds to $\sim$25 au and is almost an order of magnitude better than in the previous studies of this object. The observations were performed with ALMA at a wavelength of 0.9 mm in continuum and in several molecular lines. In the continuum we detected the central bright source (brightness temperature $\sim$850 K) elongated along the jet direction and two pairs of bright knots in the jet lobes. These pairs of knots imply a double ejection from NIRS3 with the time interval of $\sim$1.5 years. The orientation of the jet differs by $\sim$20$^\circ$ from that on larger scales, as mentioned also in some other recent works. The 0.9 mm continuum emission of the central source represents a mixture of the dust thermal emission and free-free emission of the ionized gas. Properties of the free-free emission are typical for hypercompact H II regions. In the continuum emission of the knots in the jet the free-free component apparently dominates. In the molecular lines a sub-Keplerian disk around NIRS3 about 400 au in diameter is observed. The absorption features in the molecular lines towards the central bright source may indicate an infall. The molecular line emission appears very inhomogeneous at small scales, which may indicate a small-scale clumpiness in the disk.

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arXiv2024

Study of the high-mass star-forming region S255IR at various scales

The S255IR-SMA1 core contains the protostar NIRS3 with a mass of $\sim$20 M$_\odot$. Several years ago, the first burst of luminosity for massive protostars, caused by an episodic accretion event, was recorded here. We have been studying this object for a long time using various instruments, including ALMA. The general morphology and kinematics of this area have been investigated. Disk-shaped structures, jets and outflows have been identified and studied in detail. We recently observed this object with ALMA with a resolution an order of magnitude higher than previously achieved - about 15 milliarcseconds, which corresponds to about 25 AU. This paper presents new results from the analysis of these data together with observations in other bands. The new data show an inhomogeneous disk structure, an ionized region around the protostar, and the presence of a jet observed in the submillimeter continuum, consisting of individual knots, the orientation of which differs markedly from that on large scales. The submillimeter emission from the jet most likely represents bremsstrahlung from ionized gas. Based on observations of the lines of some molecules, the kinematics and physical characteristics of this region are discussed. Methanol maser emission associated with the jet is observed.

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arXiv2024

Study of the physical and chemical properties of dense clumps in several high-mass star-forming regions

Massive stars play an important role in the Universe. Unlike low-mass stars, the formation of these objects located at great distances is still unclear. It is expected to be governed by some combination of self-gravity, turbulence, and magnetic fields. Our aim is to study of the chemical and physical conditions of dense clumps in several high-mass star-forming regions. We performed observations towards 5 high-mass star-forming regions (L1287, S187, S231, DR21(OH), NGC7538) with the IRAM 30 m telescope. We covered the 2-3 and 4 mm wavelength band and analyzed the lines of HCN, HNC, HCO$^+$, HC$_3$N, HNCO, OCS, CS, SiO, SO$_2$ and SO. Using astrodendro algorithm on the 850 $μ$m dust emission data from the SCUBA Legacy catalogue, we identified dense gas clumps and determined their masses, H$_2$ column densities and sizes. Furthermore, the kinetic temperatures, molecular abundances and dynamical state were obtained. The Red Midcourse Space Experiment Source survey (RMS) was used to determine the clump types. We identified $\sim$20 clumps. We found no significant correlation between line width and size, but the linewidth-mass and mass-size relationships are strongly correlated. Virial analysis indicated that the clumps with HII regions and young stellar objects (YSOs) are gravitationally bound. Furthermore, it was suggested that significant magnetic fields provide additional support for clump stability. The molecular abundances decrease from YSOs to submm and HII regions.

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arXiv2023

Fragmentation and dynamics of dense gas structures in the proximity of massive young stellar object W42-MME

We present an analysis of the dense gas structures in the immediate surroundings of the massive young stellar object (MYSO) W42-MME, using the high-resolution (0$''$.31$\times$0$''$.25) ALMA dust continuum and molecular line data. We performed a dendrogram analysis of H$^{13}$CO$^{+}$ (4-3) line data to study multi-scale structures and their spatio-kinematic properties, and analyzed the fragmentation and dynamics of dense structures down to $\sim$2000 AU scale. Our results reveal 19 dense gas structures, out of which 12 are leaves and 7 are branches in dendrogram terminology. These structures exhibit transonic-supersonic gas motions (1$<\mathcal{M}<5$) with overvirial states ($α_{\rm vir}\geq2$). The non-thermal velocity dispersion-size relation ($σ_{\rm nt}-L$) of dendrogram structures shows a weak negative correlation, while the velocity dispersion across the sky ($δ\mathit{V_{\rm lsr}}$) correlates positively with structure size ($L$). Velocity structure function ($S_{2}(l)^{1/2}$) analysis of H$^{13}$CO$^{+}$ data reveals strong power-law dependencies with lag ($l$) up to a scale length of $\lesssim$ 6000 AU. The mass-size ($M-R$) relation of dendrogram structures shows a positive correlation with power-law index of 1.73$\pm$0.23, and the leaf L17 hosting W42-MME meets the mass-size conditions for massive star formation. Blue asymmetry is observed in the H$^{12}$CO$^{+}$ (4-3) line profiles of most of the leaves, indicating infall. Overall, our results observationally support the hierarchical and chaotic collapse scenario in the proximity of the MYSO W42-MME.

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arXiv2023

Variations of the HCO$^{+}$, HCN, HNC, N$_2$H$^+$ and NH$_{3}$ deuterium fractionation in high-mass star-forming regions

We use spectra and maps of the $J=1-0$ and $J=2-1$ DCO$^{+}$, DCN, DNC, $\rm N_2D^+$ lines and $1_{11}-1_{01}$ ortho- and para-NH$_{2}$D lines, obtained with the IRAM-30m telescope, as well as observations of their hydrogenated isotopologues to study deuteration processes in five high-mass star-forming regions. The temperature was estimated from CH$_3$CCH lines, also observed with the IRAM-30m telescope, and from NH$_3$ lines, observed with the 100-m radio telescope in Effelsberg, as well as using the integrated intensity ratios of the $J=1-0$ H$^{13}$CN and HN$^{13}$C lines and their main isotopologues. Applying a non-LTE radiative transfer model with RADEX, the gas density and the molecular column densities were estimated. D/H ratios are $0.001-0.05$ for DCO$^{+}$, $0.001-0.02$ for DCN, $0.001-0.05$ for DNC and $0.02-0.4$ for NH$_{2}$D. The D/H ratios decrease with increasing temperature in the range of $\rm 20-40 \,K$ and slightly vary at densities $n(\rm H_2) \sim 10^4-10^6\, cm^{-3}$. The deuterium fraction of $\rm N_2H^{+}$ is $0.008-0.1$ at temperatures in the range of $\rm 20-25\, K$ and at a density of $\sim 10^5\, \rm cm^{-3}$. We also estimate relative abundances and find $ \sim 10^{-11}-10^{-9}$ for DCO$^{+}$ and DNC, $ \sim 10^{-11}-10^{-10}$ for $\rm N_2D^+$ and $ \sim 10^{-10}-10^{-8}$ for NH$_{2}$D. The relative abundances of these species decrease with increasing temperature. However, the DCN/H$_2$ ratio is almost constant ($\sim 10^{-10}$). The observational results agree with the predictions of chemical models (although in some cases there are significant differences).

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arXiv2022

H$^{13}$CN-HN$^{13}$C intensity ratio as a temperature indicator of interstellar clouds

With the 30-m IRAM radio telescope, we observed several massive star forming regions at wavelengths of 3-4 and 2 mm. The temperature of the gas in the sources was estimated from the lines of CH$_{3}$CCH and from the transitions of the NH$_3$ molecule obtained during observations at the 100-m radio telescope in Effelsberg. As a result, a correlation between the integrated intensity ratios of the $J=1-0$ transitions of H$^{13}$CN and HN$^{13}$C and the kinetic temperature has been obtained. The obtained results allow us to propose the use of the intensity ratio H$^{13}$CN-HN$^{13}$C as a possible temperature indicator of interstellar clouds. We also compared the obtained estimates of the kinetic temperature with the dust temperature $T_{dust}$. As a result, no significant correlation was found.

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arXiv2022

LOFAR detection of faint radio emission from the supernova remnant SRGeJ0023+3625=G116.6-26.1: probing the Milky Way synchrotron halo

A supernova remnant (SNR) candidate SRGe~J0023+3625 = G116.6-26.1 was recently discovered in the \textit{SRG}/eROSITA all-sky X-ray survey. This large ($\sim 4$ deg in diameter) SNR candidate lacks prominent counterparts in other bands. Here we report detection of radio emission from G116.6-26.1 in the LOFAR Two-metre Sky Survey (LoTTS-DR2). Radio images show a shell-like structure coincident with the X-ray boundary of the SNR. The measured surface brightness of radio emission from this SNR is very low. Extrapolation of the observed surface brightness to 1~GHz places G116.6-26.1 well below other objects in the $Σ-D$ diagram. We argue that the detected radio flux might be consistent with the minimal level expected in the van der Laan adiabatic compression model, provided that the volume emissivity of the halo gas in the LOFAR band is $\sim 10^{-42}\,{\rm Wm^{-3}Hz^{-1} sr^{-1}}$. If true, this SNR can be considered as a prototypical example of an evolved SNR in the Milky Way halo. In the X-ray and radio bands, such SNRs can be used as probes of thermal and non-thermal components constituting the Milky Way halo.

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arXiv2021

The disk-outflow system around the rare young O-type protostar W42-MME

We present line and continuum observations (resolution ~0.3"-3.5") made with the Atacama Large Millimeter/submillimeter Array (ALMA), Submillimeter Array, and Very Large Array of a young O-type protostar W42-MME (mass: 19-4 Msun). The ALMA 1.35 mm continuum map (resolution ~1") shows that W42-MME is embedded in one of the cores (i.e., MM1) located within a thermally supercritical filament-like feature (extent ~0.15 pc) containing three cores (mass ~1-4.4 Msun). Several dense/hot gas tracers are detected toward MM1, suggesting the presence of a hot molecular core with the gas temperature of ~38-220~K. The ALMA 865 micron continuum map (resolution ~0.3") reveals at least five continuum sources/peaks ("A-E") within a dusty envelope (extent ~9000 AU) toward MM1, where shocks are traced in the SiO(8-7) emission. The source "A" associated with W42-MME is seen almost at the center of the dusty envelope, and is surrounded by other continuum peaks. The ALMA CO(3-2) and SiO(8-7) line observations show the bipolar outflow extended below 10000 AU, which is driven by the source "A". The ALMA data hint the episodic ejections from W42-MME. A disk-like feature (extent ~2000 AU; mass ~1 Msun) with velocity gradients is investigated in the source "A" (dynamical mass ~9 Msun) using the ALMA H13CO+ emission, and is perpendicular to the CO outflow. A small-scale feature (below 3000 AU) probably heated by UV radiation from the O-type star is also investigated toward the source "A". Overall, W42-MME appears to gain mass from its disk and the dusty envelope.

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arXiv2021

Probing gas kinematics and PDR structure around O-type stars in Sh 2-305 HII region

We report an observational study of the Galactic HII region Sh 2-305/S305 using the [CII] 158 $μ$m line data, which are used to examine the gas dynamics and structure of photodissociation regions. The integrated [CII] emission map at [39.4, 49.5] km s$^{-1}$ spatially traces two shell-like structures (i.e., inner and outer neutral shells) having a total mass of $\sim$565 M$_\odot$. The inner neutral shell encompasses an O9.5V star at its centre and has a compact ring-like appearance. However, the outer shell is seen with more extended and diffuse [CII] emission, hosting an O8.5V star at its centre and surrounds the inner neutral shell. The velocity channel maps and position-velocity diagrams confirm the presence of a compact [CII] shell embedded in the diffuse outer shell, and both the shells seem to expand with $v_{\rm exp}\sim$1.3 km s$^{-1}$. The outer shell appears to be older than the inner shell, hinting that these shells are formed sequentially. The [CII] profiles are examined toward S305, which are either double-peaked or blue-skewed and have the brighter redshifted component. The redshifted and blueshifted components spatially trace the inner and outer neutral shell geometry, respectively. The ionized, neutral, and molecular zones in S305 are seen adjacent to one another around the O-type stars. The regularly spaced dense molecular and dust clumps (mass $\sim$10-10$^{3}$ M$_{\odot}$) are investigated around the neutral shells, which might have originated due to gravitational instability in the shell of collected materials.

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arXiv2021

SRG/eROSITA discovery of a large circular SNR candidate G116.6-26.1: SN Ia explosion probing the gas of the Milky Way halo?

We report a discovery of a new X-ray-selected supernova remnant (SNR) candidate SRGe~J0023+3625 = G116.6-26.1 found in the SRG/eROSITA all-sky survey. The source features a large angular extent ($\sim 4$ deg in diameter), nearly circular shape and X-ray spectrum dominated by emission lines of helium- and hydrogen-like oxygen. It lacks bright counterparts of similar extent at other wavelengths which could be unequivocally associated with it. Given the relatively high Galactic latitude of the source, $b\approx-26$ deg, we interpret these observational properties as an indication of the off-disk location of this SNR candidate. Namely, we propose that this object originated from a Type Ia supernova which exploded some 40 000 yr ago in the low density ($\sim 10^{-3}\,{\rm cm^{-3}}$) and hot ($\sim (1-2)\times10^6\,{\rm K}$) gas of the Milky Way halo at a distance of $\sim 3\,{\rm kpc}$ from the Sun. The low density of the halo gas implies that the cooling and collisional ionization equilibrium (CEI) timescales downstream of the forward shock are much longer than the age of the SNR. This results in a relatively soft spectrum, reflecting pre-shock ionization state of the gas, and strong boost in the plasma emissivity (compared to CEI) due to enhanced collisional excitation through the increased electron temperature. If confirmed, such a rare object would provide us with a unique "in situ" probe of physical conditions (density, temperature and metallicity) near the interface between the Milky Way's disk and the halo.

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arXiv2021

ALMA discovery of a dual dense probably rotating outflow from a massive young stellar object G18.88MME

We report the discovery of a very dense jet-like fast molecular outflow surrounded by a wide-angle wind in a massive young stellar object (MYSO) G18.88MME (stellar mass $\sim$8 M$_{\odot}$) powering an Extended Green Object G18.89$-$0.47. Four cores MM1-4 are identified in the Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum map (resolution $\sim$0.$"$8) toward G18.88MME, and are seen at the center of the emission structure (extent $\sim$0.3 pc $\times$ 0.2 pc) detected in the ALMA map. G18.88MME is embedded in the core MM1 (mass $\sim$13-18 M$_{\odot}$), where no radio continuum emission is detected. The molecular outflow centered at MM1 is investigated in the SiO(5-4), HC$_{3}$N(24-23) and $^{13}$CO(2-1) lines. The detection of HC$_{3}$N in the outflow is rare in MYSOs and indicates its very high density. The position-velocity diagrams display a fast narrow outflow (extent $\sim$28000 AU) and a slower wide-angle more extended outflow toward MM1, and both of these components show a transverse velocity gradient indicative of a possible rotation. All these observed features together make G18.88MME as a unique object for studying the unification of the jet-driven and wind-driven scenarios of molecular outflows in MYSOs.

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arXiv2021

A multi-line study of the filamentary infrared dark cloud G351.78-0.54

We present results of a multi-line study of the filamentary infrared dark cloud G351.78-0.54 in the 1.3 and 0.8 mm wavelength bands. The lines of the three isotopologues of carbon monoxide CO, N$_2$H$^+$, CH$_3$CCH and HNCO were observed. The aim was to study the general structure of the filamentary cloud, its fragmentation and physical parameters with the emphasis on properties of dense clumps in this cloud. Several dense clumps are identified from the N$_2$H$^+$ (3-2) data, their masses and virial parameters are determined using the C$^{18}$O (2-1) line. Temperatures of some clumps are estimated from the CH$_3$CCH and HNCO data. Almost all clumps appear to be gravitationally unstable. The density estimates obtained from the C$^{18}$O (3-2)/(2-1) and N$_2$H$^+$ (3-2)/(1-0) intensity ratios are in the range $n \sim (0.3-3)\times 10^5$ cm$^{-2}$. The HNCO emission is detected exclusively toward the first clump which contains the luminous IR source IRAS 17233-3606, and indicates an even higher density. It is observed in the outflow, too. The velocity shift of the higher excitation HNCO lines may indicate a movement of the hot core relative the surrounding medium. In some clumps there is a velocity shift $\sim 1$ km s$^{-1}$ between N$_2$H$^+$ (3-2) and CO isotopologues. The large widths of the N$_2$H$^+$ (3-2) line in the clumps indicate an increase of the velocity dispersion in their dense interiors, which may be related to the star formation process. The N$_2$H$^+$ abundance drops toward the luminous IR source.

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arXiv2018

The Spatial-Kinematic Structure of the Region of Massive Star Formation S255N on Various Scales

The results of a detailed analysis of SMA, VLA, and IRAM observations of the region of massive star formation S255N in CO(2---1), \nh, \nhh, \co and some other lines is presented. Combining interferometer and single-dish data has enabled a more detailed investigation of the gas kinematics in the moleclar core on various spatial scales. There are no signs of rotation or isotropic compression on the scale of the region as whole. The largest fragments of gas ($\approx$0.3 pc) are located near the boundary of the regions of ionized hydrogen S255 and S257. Some smaller-scale fragments are associated with protostellar clumps. The kinetic temperatures of these fragments lie in the range 10---80 K. A circumstellar torus with inner radius R$_{in}$ $\approx$ 8000 AU and outer radius R$_{out}$ 12 000 AU has been detected around the clump SMA1. The rotation profile indicates the existence of a central object with mass $\approx$ 8.5/ sin 2 (i) M$_\odot$ . SMA1 is resolved into two clumps, SMA1---NE and SMA1---SE, whose temperatures are $\approx$150 K and $\approx$25 K, respectively. To all appearances, the torus is involved in the accretion of surrounding gas onto the two protostellar clumps.

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