scholarly journals Search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS)

2018 ◽  
Vol 617 ◽  
pp. A89 ◽  
Author(s):  
T. Csengeri ◽  
S. Bontemps ◽  
F. Wyrowski ◽  
A. Belloche ◽  
K. M. Menten ◽  
...  
Keyword(s):  
Excited State ◽  
Accretion Disc ◽  
High Mass ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
High Excitation ◽  
Vibrationally Excited ◽  
Bolometric Luminosity ◽  
Physical Scale ◽  
Low Mass

The conditions leading to the formation of the most massive O-type stars are still an enigma in modern astrophysics. To assess the physical conditions of high-mass protostars in their main accretion phase, here we present a case study of a young massive clump selected from the ATLASGAL survey, G328.2551–0.5321. The source exhibits a bolometric luminosity of 1.3 × 104 L⊙, which allows us to estimate that its current protostellar mass lies between ~11 and 16 M⊙. We show high angular resolution observations with ALMA that reach a physical scale of ~400 au. To reveal the structure of this high-mass protostellar envelope in detail at a ~0.17′′ resolution, we used the thermal dust continuum emission and spectroscopic information, amongst others from the CO (J = 3–2) line, which is sensitive to the high-velocity molecular outflow of the source. We also used the SiO (J = 8–7) and SO2 (J = 82,6 − 71,7) lines, which trace shocks along the outflow, as well as several CH3OH and HC3N lines that probe the gas of the inner envelope in the closest vicinity of the protostar. Our observations of the dust continuum emission reveal a single high-mass protostellar envelope, down to our resolution limit. We find evidence for a compact, marginally resolved continuum source that is surrounded by azimuthal elongations that could be consistent with a spiral pattern. We also report on the detection of a rotational line of CH3OH within its vt = 1 torsionally excited state. This shows two bright emission peaks that are spatially offset from the dust continuum peak and exhibit a distinct velocity component ±4.5 km s−1 offset from the systemic velocity of the source. Rotational diagram analysis and models based on local thermodynamic equilibrium assumption require high CH3OH column densities that reach N(CH3OH) = 1.2−2 × 1019 cm−2, and kinetic temperatures of the order of 160–200 K at the position of these peaks. A comparison of their morphology and kinematics with those of the outflow component of the CO line and the SO2 line suggests that the high-excitation CH3OH spots are associated with the innermost regions of the envelope. While the HC3N v7 = 0 (J = 37–36) line is also detected in the outflow, the HC3N v7 = 1e (J = 38–37) rotational transition within the first vibrationally excited state of the molecule shows a compact morphology. We find that the velocity shifts at the position of the observed high-excitation CH3 OH spots correspond well to the expected Keplerian velocity around a central object with 15 M⊙ consistent with the mass estimate based on the bolometric luminosity of the source. We propose a picture where the CH3 OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disc. The physical properties of the accretion disc inferred from these observations suggest a specific angular momentum several times higher than typically observed towards low-mass protostars. This is consistent with a scenario of global collapse setting on at larger scales that could carry a more significant amount of kinetic energy compared to the core-collapse models of low-mass star formation. Furthermore, our results suggest that vibrationally excited HC3 N emission could be a new tracer for compact accretion discs around high-mass protostars.

scholarly journals Fragmentation of a Protostellar Core: The Case of CB 230

2001 ◽  
Vol 200 ◽  
pp. 117-121 ◽  
Author(s):  
Ralf Launhardt
Keyword(s):  
Main Sequence ◽  
Angular Resolution ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
Binary Separation ◽  
Molecular Outflow ◽  
Low Mass ◽  
Core Fragmentation

The Bok globule CB230 (L1177) contains an active, low-mass star-forming core which is associated with a double NIR reflection nebula, a collimated bipolar molecular outflow, and strong mm continuum emission. The morphology of the NIR nebula suggests the presence of a deeply embedded, wide binary protostellar system. High-angular resolution observations now reveal the presence of two sub-cores, two distinct outflow centers, and an embedded accretion disk associated with the western bipolar NIR nebula. Judging from the separation and specific angular momentum, the CB230 double protostar system probably results from core fragmentation and will end up at the upper end of the pre-main sequence binary separation distribution.

scholarly journals Fragmentation and dynamics in Massive Dense Cores in Cygnus-X

2010 ◽  
Vol 6 (S270) ◽  
pp. 53-56 ◽  
Author(s):  
T. Csengeri ◽  
S. Bontemps ◽  
N. Schneider ◽  
F. Motte
Keyword(s):  
Angular Resolution ◽  
High Density ◽  
High Mass ◽  
High Angular Resolution ◽  
Low Mass Stars ◽  
Dense Cores ◽  
Evolutionary Scenario ◽  
Low Mass ◽  
Molecular Tracers ◽  
Resolution Study

AbstractA systematic, high angular-resolution study of IR-quiet Massive Dense Cores (MDCs) of Cygnus-X in continuum and high-density molecular tracers is presented. The results are compared with the quasi-static and the dynamical evolutionary scenario. We find that the fragmentation properties are not compatible with the quasi-static, monolithic collapse scenario, nor are they entirely compatible with the formation of a cluster of mostly low-mass stars. The kinematics of MDCs shows individual velocity components appearing as coherent flows, which indicate important dynamical processes at the scale of the mass reservoir around high-mass protostars.

scholarly journals Molecular analysis of a high-mass prestellar core candidate in W43-MM1

2019 ◽  
Vol 626 ◽  
pp. A132 ◽  
Author(s):  
J. Molet ◽  
N. Brouillet ◽  
T. Nony ◽  
A. Gusdorf ◽  
F. Motte ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Continuum Emission ◽  
Mass Star ◽  
Star Forming ◽  
Prestellar Cores ◽  
Low Mass ◽  
Lower Temperature ◽  
Diagram Analysis ◽  
The Continuum

Context. High-mass analogues of low-mass prestellar cores are searched for to constrain the models of high-mass star formation. Several high-mass cores, at various evolutionary stages, have been recently identified towards the massive star-forming region W43-MM1 and amongst them a high-mass prestellar core candidate. Aims. We aim to characterise the chemistry in this high-mass prestellar core candidate, referred to as W43-MM1 core #6, and its environment. Methods. Using ALMA high-spatial resolution data of W43-MM1, we have studied the molecular content of core #6 and a neighbouring high-mass protostellar core, referred to as #3, which is similar in size and mass to core #6. We first subtracted the continuum emission using a method based on the density distribution of the intensities on each pixel. Then, from the distribution of detected molecules, we identified the molecules centred on the prestellar core candidate (core #6) and those associated to shocks related to outflows and filament formation. Then we constrained the column densities and temperatures of the molecules detected towards the two cores. Results. While core #3 appears to contain a hot core with a temperature of about 190 K, core #6 seems to have a lower temperature in the range from 20 to 90 K from a rotational diagram analysis. We have considered different source sizes for core #6 and the comparison of the abundances of the detected molecules towards the core with various interstellar sources shows that it is compatible with a core of size 1000 au with T = 20−90 K or a core of size 500 au with T ~ 80 K. Conclusions. Core #6 of W43-MM1 remains one of the best high-mass prestellar core candidates even if we cannot exclude that it is at the very beginning of the protostellar phase of high-mass star formation.

scholarly journals Extreme fragmentation and complex kinematics at the center of the L1287 cloud

2019 ◽  
Vol 621 ◽  
pp. A140 ◽  
Author(s):  
Carmen Juárez ◽  
Hauyu Baobab Liu ◽  
Josep M. Girart ◽  
Aina Palau ◽  
Gemma Busquet ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Angular Resolution ◽  
Spatial Scales ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Dense Gas ◽  
Continuum Image ◽  
Velocity Gradients ◽  
Low Mass

Aims. The filamentary ~10-pc-scale infrared dark cloud L1287 located at a parallax distance of ~929 pc is actively forming a dense cluster of low-mass young stellar objects (YSOs) at its inner ~0.1 pc region. To help understand the origin of this low-mass YSO cluster, the present work aims at resolving the gas structures and kinematics with high angular resolution. Methods. We performed ~1′′ angular resolution (~930 AU) observations at ~1.3 mm wavelengths using the Submillimeter Array (SMA), which simultaneously cover the dust continuum emission and various molecular line tracers for dense gas, warm gas, shocks, and outflows. Results. From a 1.3-mm continuum image with a resolution of ~2′′ we identified six dense cores, namely SMA1-6. Their gas masses are in the range of ~0.4–4 M⊙. From a 1.3-mm continuum image with a resolution of ~1′′, we find a high fragmentation level, with 14 compact millimeter sources within 0.1 pc: SMA3 contains at least nine internal condensations; SMA5 and SMA6 are also resolved with two internal condensations. Intriguingly, one condensation in SMA3 and another in SMA5 appear associated with the known accretion outburst YSOs RNO 1C and RNO 1B. The dense gas tracer DCN (3–2) well traces the dust continuum emission and shows a clear velocity gradient along the NW-SE direction centered at SMA3. There is another velocity gradient with opposite direction around the most luminous YSO, IRAS 00338 + 6312. Conclusions. The fragmentation within 0.1 pc in L1287 is very high compared to other regions at the same spatial scales. The incoherent motions of dense gas flows are sometimes interpreted by being influenced by (proto)stellar feedback (e.g., outflows), which is not yet ruled out in this particular target source. On the other hand, the velocities (with respect to the systemic velocity) traced by DCN are small, and the directions of the velocity gradients traced by DCN are approximately perpendicular to those of the dominant CO outflow(s). Therefore, we alternatively hypothesize that the velocity gradients revealed by DCN trace the convergence from the ≳0.1 pc scales infalling motion towards the rotational motions around the more compact (~0.02 pc) sources. This global molecular gas converging flow may feed the formation of the dense low-mass YSO cluster. Finally, we also found that IRAS 00338 + 6312 is the most likely powering source of the dominant CO outflow. A compact blue-shifted outflow from RNO 1C is also identified.

scholarly journals A 10-M⊙ YSO with a Keplerian disk and a nonthermal radio jet

2019 ◽  
Vol 622 ◽  
pp. A206 ◽  
Author(s):  
L. Moscadelli ◽  
A. Sanna ◽  
R. Cesaroni ◽  
V. M. Rivilla ◽  
C. Goddi ◽  
...  
Keyword(s):  
Dust Emission ◽  
Major Axis ◽  
High Mass ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Central Mass ◽  
Disk Radius ◽  
Dynamical Interaction ◽  
Linear Pattern ◽  
Nonthermal Radio

Context. To constrain present star formation models, we need to simultaneously establish the dynamical and physical properties of disks and jets around young stars. Aims. We previously observed the star-forming region G16.59−0.05 through interferometric observations of both thermal and maser lines, and identified a high-mass young stellar object (YSO) which is surrounded by an accretion disk and drives a nonthermal radio jet. Our goals are to establish the physical conditions of the environment hosting the high-mass YSO and to study the kinematics of the surrounding gas in detail. Methods. We performed high-angular-resolution (beam FWHM ≈ 0′′.15) 1.2-mm continuum and line observations towards G16.59−0.05 with the Atacama Large Millimeter Array (ALMA). Results. The main dust clump, with size ≈104 au, is resolved into four distinct, relatively compact (diameter ~2000 au) millimeter (mm) sources. The source harboring the high-mass YSO is the most prominent in molecular emission. By fitting the emission profiles of several unblended and optically thin transitions of CH3OCH3 and CH3OH, we derived gas temperatures inside the mm sources in the range 42–131 K, and calculated masses of 1–5 M⊙. A well-defined Local Standard of Rest (LSR) velocity (VLSR) gradient is detected in most of the high-density molecular tracers at the position of the high-mass YSO, pinpointed by compact 22-GHz free-free emission. This gradient is oriented along a direction forming a large (≈70°) angle with the radio jet, traced by elongated 13-GHz continuum emission. The butterfly-like shapes of the P–V plots and the linear pattern of the emission peaks of the molecular lines at high velocity confirm that this VLSR gradient is due to rotation of the gas in the disk surrounding the high-mass YSO. The disk radius is ≈500 au, and the VLSR distribution along the major axis of the disk is well reproduced by a Keplerian profile around a central mass of 10 ± 2 M⊙. The position of the YSO is offset by ≳0′′.1 from the axis of the radio jet and the dust emission peak. To explain this displacement we argue that the high-mass YSO could have moved from the center of the parental mm source owing to dynamical interaction with one or more companions.

scholarly journals Submillimetre polarimetric observations of magnetic fields in star-forming regions

2007 ◽  
Vol 3 (S243) ◽  
pp. 63-70
Author(s):  
Rachel L. Curran ◽  
Antonio Chrysostomou ◽  
Brenda C. Matthews
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Cumulative Distribution ◽  
High Mass ◽  
Continuum Emission ◽  
Field Pattern ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
The Magnetic Field

AbstractSubmillimetre imaging polarimetry is one of the most powerful tools at present for studying magnetic fields in star-forming regions, and the only way to gain significant information on the structure of these fields. We present analysis of the largest sample (to date) of both high- and low-mass star-forming regions observed using this technique. A variety of magnetic field morphologies are observed, with no single field morphology favoured. Both the continuum emission morphologies and the field morphologies are generally more complex for the high-mass sample than the low-mass sample. The large scale magnetic field (observed with the JCMT; 14″ resolution) of NGC1333 IRAS2 is interpreted to be weak (compared to the energetic contributions due to turbulence) from the random field pattern observed. On smaller scales (observed with the BIMA array; 3″ resolution) the field is observed to be almost radial, consistent with the polarisation nulls in the JCMT data – suggesting that on smaller scales, the field may be more important to the star formation process. An analysis of the magnetic field direction and the jet/outflow axis is also discussed. Cumulative distribution functions of the difference between the mean position angle of the magnetic field vectors and the jet/outflow axis reveal no correlation. However, visual inspection of the maps reveal alignment of the magnetic field and jet/outflow axis in 7 out of 15 high-mass regions and 3 out of 8 low-mass regions.

scholarly journals APEX observations of ortho-H2D+ towards dense cores in the Orion B9 filament

2020 ◽  
Vol 634 ◽  
pp. A115
Author(s):  
O. Miettinen
Keyword(s):  
Line Emission ◽  
Spectral Lines ◽  
High Mass ◽  
Continuum Emission ◽  
Target System ◽  
Gas Temperature ◽  
Star Forming ◽  
Dense Cores ◽  
Prestellar Cores ◽  
Low Mass

Context. Initial conditions and very early stages of star formation can be probed through spectroscopic observations of deuterated molecular species Aims. We aim to determine the ortho-H2D+ properties (e.g. column density and fractional abundance with respect to H2) in a sample of dense cores in the Orion B9 star-forming filament, and to compare those with the previously determined source characteristics, in particular with the gas kinetic temperature, [N2D+]/[N2H+] deuterium fractionation, and level of CO depletion. Methods. We used the Atacama Pathfinder EXperiment (APEX) telescope to observe the 372 GHz o-H2D+(JKa, Kc = 11, 0−11, 1) line towards three prestellar cores and three protostellar cores in Orion B9. We also employed our previous APEX observations of C17O, C18O, N2H+, and N2D+ line emission, and 870 μm dust continuum emission towards the target sources. Results. The o-H2D+(11, 0−11, 1) line was detected in all three prestellar cores, but in only one of the protostellar cores. The corresponding o-H2D+ abundances were derived to be ~ (12−30) × 10−11 and ~ 6 × 10−11. Two additional spectral lines, DCO+(5−4) and N2H+(4−3), were detected in the observed frequency bands with high detection rates of 100 and 83%, respectively. We did not find any significant correlations among the explored parameters, although our results are mostly consistent with theoretical expectations. Also, the Orion B9 cores were found to be consistent with the relationship between theo-H2D+ abundance and gas temperature obeyed by other low-mass dense cores. The o-H2D+ abundance was found to decrease as the core evolves. Conclusions. The o-H2D+ abundances in the Orion B9 cores are in line with those found in other low-mass dense cores and larger than derived for high-mass star-forming regions. The higher o-H2D+ abundance in prestellar cores compared to that in cores hosting protostars is to be expected from chemical reactions where higher concentrations of gas-phase CO and elevated gas temperature accelerate the destruction of H2D+. The validity of using the [o-H2D+]/[N2D+] abundance ratio as an evolutionary indicator, which has been proposed for massive clumps, remains to be determined when applied to these target cores. Similarly, the behaviour of the [o-H2D+]/[DCO+] ratio as the source evolves was found to be ambiguous. Still larger samples and observations of additional deuterated species are needed to explore these potential evolutionary indicators further. The low radial velocity of the line emission from one of the targeted prestellar cores, SMM 7 (~ 3.6 km s−1 versus the systemic Orion B9 velocity of ~ 9 km s−1), suggests that it is a chance superposition seen towards Orion B9. Overall, as located in a dynamic environment of the Orion B molecular cloud, the Orion B9 filament provides an interesting target system to investigate the deuterium-based chemistry, and further observations of species like para-H2D+ and D2H+ would be of particular interest.

scholarly journals Molecular complexity on disc scales uncovered by ALMA

2019 ◽  
Vol 628 ◽  
pp. A2 ◽  
Author(s):  
Eva G. Bøgelund ◽  
Andrew G. Barr ◽  
Vianney Taquet ◽  
Niels F. W. Ligterink ◽  
Magnus V. Persson ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Chemical Composition ◽  
Column Density ◽  
Angular Resolution ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Complex Species ◽  
Low Mass

Context. The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In addition, the spatial distribution and velocity structure of different molecular species provide valuable information on the physical structure of these embedded objects. Despite an increasing number of interferometric studies, there is still a high demand for high angular resolution data to study chemical compositions and velocity structures for these objects. Aims. The molecular inventory of the forming high-mass star AFGL 4176, located at a distance of ~3.7 kpc, is studied in detail at a high angular resolution of ~0.35′′, equivalent to ~1285 au at the distance of AFGL 4176. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disc around the forming star from that of its cool outer envelope. The composition of AFGL 4176 is compared with other high- and low-mass sources, and placed in the broader context of star formation. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA) the chemical inventory of AFGL 4176 has been characterised. The high sensitivity of ALMA made it possible to identify weak and optically thin lines and allowed for many isotopologues to be detected, providing a more complete and accurate inventory of the source. For the detected species, excitation temperatures in the range 120–320 K were determined and column densities were derived assuming local thermodynamic equilibrium and using optically thin lines. The spatial distribution of a number of species was studied. Results. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH) with a column density of 5.5 × 1018 cm−2 in a beam of ~0.3′′, derived from its 13C-isotopologue. The remaining species are present at levels between 0.003 and 15% with respect to methanol. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. A single species, propyne (CH3C2H), displays a double-peaked distribution. Conclusions. AFGL 4176 comprises a rich chemical inventory including many complex species present on disc scales. On average, the derived column density ratios, with respect to methanol, of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293–2422B than that of high-mass, star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar.

scholarly journals Detection of a high-mass prestellar core candidate in W43-MM1

2018 ◽  
Vol 618 ◽  
pp. L5 ◽  
Author(s):  
T. Nony ◽  
F. Louvet ◽  
F. Motte ◽  
J. Molet ◽  
K. Marsh ◽  
...  
Keyword(s):  
Line Emission ◽  
High Mass ◽  
Continuum Emission ◽  
Physical Processes ◽  
Star Formation Activity ◽  
Prestellar Cores ◽  
Low Mass ◽  
Molecular Complexity ◽  
The Continuum ◽  
Main Filament

Aims. To constrain the physical processes that lead to the birth of high-mass stars it is mandatory to study the very first stages of their formation. We search for high-mass analogs of low-mass prestellar cores in W43-MM1. Methods. We conducted a 1.3 mm ALMA mosaic of the complete W43-MM1 cloud, which has revealed numerous cores with ~2000 au FWHM sizes. We investigated the nature of cores located at the tip of the main filament, where the clustering is minimum. We used the continuum emission to measure the core masses and the 13CS(5-4) line emission to estimate their turbulence level. We also investigated the prestellar or protostellar nature of these cores by searching for outflow signatures traced by CO(2-1) and SiO(5-4) line emission, and for molecular complexity typical of embedded hot cores. Results. Two high-mass cores of ~1300 au diameter and ~60 M⊙ mass are observed to be turbulent but gravitationally bound. One drives outflows and is associated with a hot core. The other core, W43-MM1#6, does not yet reveal any star formation activity and thus is an excellent high-mass prestellar core candidate.

scholarly journals Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

2020 ◽  
Vol 640 ◽  
pp. A111
Author(s):  
C. Arce-Tord ◽  
F. Louvet ◽  
P. C. Cortes ◽  
F. Motte ◽  
C. L. H. Hull ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Mass ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
The Core ◽  
Dense Cores ◽  
The Impact ◽  
The Magnetic Field

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region. Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of ~2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission. Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20–50° with respect to the magnetic field. As for the outflows, they could be oriented 50–70° with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions. Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20–50° preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

Sign in / Sign up

Export Citation Format

Share Document