scholarly journals Filamentary Flows and Clump-fed High-mass Star Formation in G22

2017 ◽  
Vol 13 (S336) ◽  
pp. 299-300 ◽  
Author(s):  
J. Yuan ◽  
J.-Z. Li ◽  
Y. Wu
Keyword(s):  
Star Formation ◽  
Accretion Rate ◽  
Free Fall ◽  
High Mass ◽  
Mass Star ◽  
The Core ◽  
Velocity Gradients ◽  
Molecular Core ◽  
Methanol Masers ◽  
Global Collapse

AbstractG22 is a hub-filament system composed of four supercritical filaments. Velocity gradients are detected along three filaments. A total mass infall rate of 700 M⊙ Myr−1 would double the hub mass in about three free-fall times. The most massive clump C1 would be in global collapse with an infall velocity of 0.26 km s−1 and a mass infall rate of 5 × 10−4M⊙ yr−1, which is supported by the prevalent HCO+ (3-2) and 13CO (3-2) blue profiles. A hot molecular core (SMA1) was revealed in C1. At the SMA1 center, there is a massive protostar (MIR1) driving multipolar outflows which are associated with clusters of class I methanol masers. MIR1 may be still growing with an accretion rate of 7 × 10−5M⊙ yr−1. Filamentary flows, clump-scale collapse, core-scale accretion coexist in G22, suggesting that high-mass starless cores may not be prerequisite to form high-mass stars. In the high-mass star formation process, the central protostar, the core, and the clump can grow in mass simultaneously.

scholarly journals ALMA resolves the hourglass magnetic field in G31.41+0.31

2019 ◽  
Vol 630 ◽  
pp. A54 ◽  
Author(s):  
M. T. Beltrán ◽  
M. Padovani ◽  
J. M. Girart ◽  
D. Galli ◽  
R. Cesaroni ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Velocity Gradient ◽  
Flux Ratio ◽  
High Mass ◽  
Continuum Emission ◽  
Mass Star ◽  
Star Forming ◽  
The Core ◽  
Molecular Core ◽  
The Magnetic Field

Context. Submillimeter Array (SMA) 870 μm polarization observations of the hot molecular core G31.41+0.31 revealed one of the clearest examples up to date of an hourglass-shaped magnetic field morphology in a high-mass star-forming region. Aims. To better establish the role that the magnetic field plays in the collapse of G31.41+0.31, we carried out Atacama Large Millimeter/ submillimeter Array (ALMA) observations of the polarized dust continuum emission at 1.3 mm with an angular resolution four times higher than that of the previous (sub)millimeter observations to achieve an unprecedented image of the magnetic field morphology. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6). The resulting synthesized beam is 0′′.28×0′′.20 which, at the distance of the source, corresponds to a spatial resolution of ~875 au. Results. The observations resolve the structure of the magnetic field in G31.41+0.31 and allow us to study the field in detail. The polarized emission in the Main core of G31.41+0.41is successfully fit with a semi-analytical magnetostatic model of a toroid supported by magnetic fields. The best fit model suggests that the magnetic field is well represented by a poloidal field with a possible contribution of a toroidal component of ~10% of the poloidal component, oriented southeast to northwest at approximately −44° and with an inclination of approximately −45°. The magnetic field is oriented perpendicular to the northeast to southwest velocity gradient detected in this core on scales from 103 to 104 au. This supports the hypothesis that the velocity gradient is due to rotation of the core and suggests that such a rotation has little effect on the magnetic field. The strength of the magnetic field estimated in the central region of the core with the Davis–Chandrasekhar-Fermi method is ~8–13 mG and implies that the mass-to-flux ratio in this region is slightly supercritical. Conclusions. The magnetic field in G31.41+0.31 maintains an hourglass-shaped morphology down to scales of <1000 au. Despite the magnetic field being important in G31.41+0.31, it is not enough to prevent fragmentation and collapse of the core, as demonstrated by the presence of at least four sources embedded in the center of the core.

scholarly journals Dynamics of cluster-forming hub-filament systems

2019 ◽  
Vol 629 ◽  
pp. A81 ◽  
Author(s):  
S. P. Treviño-Morales ◽  
A. Fuente ◽  
Á. Sánchez-Monge ◽  
J. Kainulainen ◽  
P. Didelon ◽  
...  
Keyword(s):  
Column Density ◽  
Accretion Rate ◽  
Dust Emission ◽  
Free Fall ◽  
High Mass ◽  
Hii Region ◽  
Velocity Gradients ◽  
Density Maps ◽  
The Individual ◽  
Main Filament

Context. High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest of these systems, making it an excellent target for case studies. Aims. We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. Methods. We employed observations of the 13CO and C18O 1 →0 and 2 →1 lines obtained with the IRAM-30 m telescope. We also used H2 column density maps derived from Herschel dust emission observations. Results. We identified the filamentary network in Mon R2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament). The main filaments have line masses of 30–100 M⊙ pc−1 and show signs of fragmentation, while the secondary filaments have line masses of 12–60 M⊙ pc−1 and show fragmentation only sporadically. In the context of Ostriker’s hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are transcritical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10−4–10−3 M⊙ yr−1 into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1–0.4 × 10−4 M⊙ yr−1. The main filaments extend into the central hub. Their velocity gradients increase toward the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is ~2.5 Myr, ten times longer than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring- or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.

scholarly journals A Sensitive Search for Predicted Methanol Maser Transitions with the Australia Telescope Compact Array

2016 ◽  
Vol 33 ◽  
Author(s):  
A. Chipman ◽  
S. P. Ellingsen ◽  
A. M. Sobolev ◽  
D. M. Cragg
Keyword(s):  
Star Formation ◽  
Class Ii ◽  
High Mass ◽  
Mass Star ◽  
Radio Telescopes ◽  
Methanol Maser ◽  
Upper Limit ◽  
Methanol Masers ◽  
Star Formation Regions ◽  
Compact Array

AbstractWe have used the Australia Telescope Compact Array to search for a number of centimetre wavelength methanol transitions which are predicted to show weak maser emission towards star formation regions. Sensitive, high spatial, and spectral resolution observations towards four high-mass star formation regions which show emission in a large number of class II methanol maser transitions did not result in any detections. From these observations, we are able to place an upper limit of ≲ 1300 K on the brightness temperature of any emission from the 31A+–31A−, 17−2–18−3 E (vt = 1), 124–133 A−, 124–133 A+, and 41A+–41A− transitions of methanol in these sources on angular scales of 2 arcsec. This upper limit is consistent with current models for class II methanol masers in high-mass star formation regions and better constraints than those provided here will likely require observations with next-generation radio telescopes.

scholarly journals 44 GHz Methanol Maser Surveys

2012 ◽  
Vol 8 (S287) ◽  
pp. 133-140
Author(s):  
S. E. Kurtz
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Class Ii ◽  
Class I ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Methanol Maser ◽  
Star Forming Regions ◽  
Methanol Masers

AbstractClass I 44 GHz methanol masers are not as well-known, as common, or as bright as their more famous Class II cousins at 6.7 and 12.2 GHz. Nevertheless, the 44 GHz masers are commonly found in high-mass star forming regions. At times they appear to trace dynamically important phenomena; at other times they show no obvious link to the star formation process. Here, we summarize the major observational efforts to date, including both dedicated surveys and collateral observations. The principal results are presented, some that were expected, and others that were unexpected.

scholarly journals An evolutionary sequence for high-mass star formation

2012 ◽  
Vol 8 (S292) ◽  
pp. 39-39
Author(s):  
S. L. Breen ◽  
S. P. Ellingsen
Keyword(s):  
Star Formation ◽  
Strong Evidence ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Evolutionary Sequence ◽  
Subsequent Work ◽  
Star Forming ◽  
Methanol Maser ◽  
Methanol Masers

AbstractDetermining an evolutionary clock for high-mass star formation is an important step towards realizing a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. Our recent studies have shown that masers have great potential to accurately trace the evolution of these regions. We have investigated the relative evolutionary phases associated with the presence of combinations of water, methanol and hydroxyl masers. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species, a result that we now aim to corroborate through comparisons with chemical clocks.Using our new, large samples of methanol masers at 6.7 GHz (MMB survey; Green et al. (2009)) and 12.2 GHz (Breen et al. 2012), 22 GHz water masers (Breen & Ellingsen 2012), OH masers together with complementary data, we find strong evidence that it is not only the presence or absence of the different maser species that indicates the evolutionary stage of the associated high-mass star formation region (see e.g. Breen et al. (2010)), but that the properties of those masers can give even finer evolutionary details. Most notably, the intensity and velocity range of detected maser emission increases as the star forming region evolves (Breen et al. 2011).Subsequent work we have undertaken (Ellingsen et al. 2011) has shown that the presence of rare 37.7 GHz methanol masers may signal the end of the methanol maser phase. They show that 37.7 GHz methanol masers are associated only with the most luminous 6.7 and 12.2 GHz methanol masers, which combined with the rarity of these objects is consistent with them being a short lived phase towards the end of the 6.7 GHz methanol maser lifetime.An independent confirmation of our maser evolutionary timeline can be gained through comparisons with chemical clocks. MALT90 is a legacy survey of 1000s of dense star forming cores at 90GHz, simultaneously observing 16 molecular lines with the Mopra radio telescope (see e.g. Foster et al. 2011). It provides the perfect dataset to test the maser evolutionary timeline due to the targeted lines and the fact that at least one-quarter of the MALT90 sources correspond to maser sites, providing a large enough sample for meaningful analysis. From our preliminary analysis, we find that star formation regions showing similar maser properties also show similar thermal line properties; as would be expected if our evolutionary scenario were accurate.

scholarly journals Anatomy of the S255–S257 complex – triggered high-mass star formation

2006 ◽  
Vol 2 (S237) ◽  
pp. 160-164 ◽  
Author(s):  
V. Minier ◽  
N. Peretto ◽  
S. N. Longmore ◽  
M. G. Burton ◽  
R. Cesaroni ◽  
...  
Keyword(s):  
Star Formation ◽  
Hii Regions ◽  
High Mass ◽  
Molecular Gas ◽  
Mass Star ◽  
Optical Source ◽  
Methanol Maser ◽  
The North ◽  
Global Collapse ◽  
Cold Gas

AbstractWe present a multi-wavelength (NIR to radio) and multi-scale (1 AU to 10 pc) study of the S255–S257 complex of young high-mass (proto)stars. The complex consists of two evolved HII regions and a molecular gas filament in which new generations of high mass stars form. Four distinct regions are identified within this dusty filament: a young NIR/optical source cluster, a massive protostar binary, a (sub)millimetre continuum and molecular clump in global collapse and a reservoir of cold gas. Interestingly, the massive binary protostellar system is detected through methanol maser and mid-IR emission at the interface between the NIR cluster and the cold gas filament. The collapsing clump is located to the north of the NIR cluster and hosts a young high-mass star associated with an outflow that is observed in mid-IR, methanol maser and radio emission. We interpret this anatomy as the possible result of triggered star formation, starting with the formation of two HII regions, followed by the compression of a molecular gas filament in which a first generation of high-mass stars forms (the NIR cluster), which then triggers the formation of high mass protostars in its near environment (the massive protostellar binary). The global collapse of the northern clump might be due to both the expansion of the HII regions that squashes the filament. In conclusion, we witness the formation of four generations of clusters of high-mass stars in S255–S257.

scholarly journals Confirmation of the exclusive association between 6.7-GHz methanol masers and high-mass star formation regions

2013 ◽  
Vol 435 (1) ◽  
pp. 524-530 ◽  
Author(s):  
S. L. Breen ◽  
S. P. Ellingsen ◽  
Y. Contreras ◽  
J. A. Green ◽  
J. L. Caswell ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Mass Star ◽  
Methanol Masers ◽  
Star Formation Regions

scholarly journals Parallaxes of 6.7-GHz methanol masers towards the G 305.2 high-mass star formation region

2016 ◽  
Vol 465 (1) ◽  
pp. 1095-1105 ◽  
Author(s):  
V. Krishnan ◽  
S. P. Ellingsen ◽  
M. J. Reid ◽  
H. E. Bignall ◽  
J. McCallum ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Mass Star ◽  
Star Formation Region ◽  
Formation Region ◽  
Methanol Masers

scholarly journals The feedback of an HC HII region on its parental molecular core

2018 ◽  
Vol 616 ◽  
pp. A66 ◽  
Author(s):  
L. Moscadelli ◽  
V. M. Rivilla ◽  
R. Cesaroni ◽  
M. T. Beltrán ◽  
Á Sánchez-Monge ◽  
...  
Keyword(s):  
High Energy ◽  
High Mass ◽  
High Angular Resolution ◽  
Kinetic Temperature ◽  
Mass Star ◽  
Level Energy ◽  
Ionized Gas ◽  
Physical Conditions ◽  
Molecular Core ◽  
Methanol Masers

Context. G24.78+0.08 is a well known high-mass star-forming region, where several molecular cores harboring OB young stellar objects are found inside a clump of size ≈1 pc. This article focuses on the most prominent of these cores, A1, where an intense hypercompact (HC) HII region has been discovered by previous observations. Aims. Our aim is to determine the physical conditions and the kinematics of core A1, and study the interaction of the HII region with the parental molecular core. Methods. We combine ALMA 1.4 mm high-angular resolution (≈0.′′2) observations of continuum and line emission with multi-epoch Very Long Baseline Interferometry data of water 22 GHz and methanol 6.7 GHz masers. These observations allow us to study the gas kinematics on linear scales from 10 to 104 au, and to accurately map the physical conditions of the gas over core A1. Results. The 1.4 mm continuum is dominated by free-free emission from the intense HC HII region (size ≈1000 au) observed to the North of core A1 (region A1N). Analyzing the H30α line, we reveal a fast bipolar flow in the ionized gas, covering a range of LSR velocities (VLSR) of ≈60 km s−1. The amplitude of the VLSR gradient, 22 km s−1 mpc−1, is one of the highest so far observed towards HC HII regions. Water and methanol masers are distributed around the HC HII region in A1N, and the maser three-dimensional (3D) velocities clearly indicate that the ionized gas is expanding at high speed (≥200 km s−1) into the surrounding molecular gas. The temperature distribution (in the range 100–400 K) over core A1, traced with molecular (CH3OCHO, 13CH3CN, 13CH3OH, and CH3CH2CN) transitions with level energy in the range 30 K ≤ Eu/k ≤ 300 K, reflects the distribution of shocks produced by the fast-expansion of the ionized gas of the HII region. The high-energy (550 K ≤ Eu/k ≤ 800 K) transitions of vibrationally excited CH3CN are likely radiatively pumped, and their rotational temperature can significantly differ from the kinetic temperature of the gas. Over core A1, the VLSR maps from both the 1.4 mm molecular lines and the 6.7 GHz methanol masers consistently show a VLSR gradient (amplitude ≈0.3 km s−1 mpc−1) directed approximately S–N. Rather than gravitationally supported rotation of a massive toroid, we interpret this velocity gradient as a relatively slow expansion of core A1.

scholarly journals Methanol masers as tools to study high-mass star formation

2007 ◽  
Vol 3 (S242) ◽  
pp. 89-96 ◽  
Author(s):  
Michele R. Pestalozzi
Keyword(s):  
Star Formation ◽  
Luminosity Function ◽  
High Mass ◽  
Mass Star ◽  
Methanol Masers

AbstractIn this contribution I will attempt to show that the study of Galactic 6.7 and 12.2 GHz methanol masers themselves, as opposed to the use of methanol masers as signposts, can yield important conclusions contributing to the understanding of high-mass star formation. Due to their exclusive association with star formation, methanol masers are the best tools to do this, and their large number allows us to probe the entire Galaxy. In particular I will focus on the determination of the luminosity function of methanol masers and on the determination of an unambiguous signature for a circumstellar masing disc seen edge-on. Finally I will try to point out some future fields of research in the study of methanol masers.

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