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 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.

Periodic methanol masers and colliding wind binaries

2017 ◽  
Vol 13 (S336) ◽  
pp. 327-328
Author(s):  
Stefanus P. van den Heever ◽  
D. J. van der Walt ◽  
J. M. Pittard ◽  
M. G. Hoare
Keyword(s):  
Hii Regions ◽  
Time Dependent ◽  
High Mass ◽  
Mass Star ◽  
Quiescent State ◽  
Ionized Gas ◽  
Driving Mechanisms ◽  
Dependent Change ◽  
Time Dependent Change ◽  
Methanol Masers

AbstractSince the discovery of periodic variability of Class II methanol masers associated with high-mass star formation, several possible driving mechanisms have been proposed to explain this phenomenon. Here the colliding wind binary (CWB) hypothesis is proposed to describe the periodic variability. It is shown that the recombination of a partially ionized gas describes the flare profiles remarkably well. In addition, the quiescent state flux density is also described remarkably well by the time-dependent change of the electron density. This suggests that the periodicity is caused by the time-dependent change in the radio free-free emission from the background HII regions against which the maser is projected.

scholarly journals Methanol and water maser observations separate disc and outflow sources in IRAS 19410+2336

2020 ◽  
Vol 493 (3) ◽  
pp. 4442-4452 ◽  
Author(s):  
M S Darwish ◽  
K A Edris ◽  
A M S Richards ◽  
S Etoka ◽  
M S Saad ◽  
...  
Keyword(s):  
Flux Density ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Star Forming ◽  
Peak Flux ◽  
Maser Line ◽  
Methanol Masers ◽  
Water Masers ◽  
Water Maser

ABSTRACT We investigate the kinematics of high-mass protostellar objects within the high-mass star-forming region IRAS 19410+2336. We performed high angular resolution observations of 6.7-GHz methanol and 22 GHz water masers using the Multi-Element Radio Linked Interferometer Network (MERLIN) and e-MERLIN interferometers. The 6.7-GHz methanol maser emission line was detected within the ∼16–27 km s−1 velocity range with a peak flux density ∼50 Jy. The maser spots are spread over ∼1.3 arcsec on the sky, corresponding to ∼2800 au at a distance of 2.16 kpc. These are the first astrometric measurements at 6.7 GHz in IRAS 19410+2336. The 22-GHz water maser line was imaged in 2005 and 2019 (the latter with good astrometry). Its velocities range from 13 to ∼29 km s−1. The peak flux density was found to be 18.7 and 13.487 Jy in 2005 and 2019, respectively. The distribution of the water maser components is up to 165 mas, ∼350 au at 2.16 kpc. We find that the Eastern methanol masers most probably trace outflows from the region of millimetre source mm1. The water masers to the West lie in a disc (flared or interacting with outflow/infall) around another more evolved millimetre source (13-s). The maser distribution suggests that the disc lies at an angle of 60° or more to the plane of the sky and the observed line-of-sight velocities then suggest an enclosed mass between 44 M⊙ and as little as 11 M⊙ if the disc is edge-on. The Western methanol masers may be infalling.

scholarly journals Investigating high-mass star formation through maser surveys

2007 ◽  
Vol 3 (S242) ◽  
pp. 213-217 ◽  
Author(s):  
S. P. Ellingsen ◽  
M. A. Voronkov ◽  
D. M. Cragg ◽  
A. M. Sobolev ◽  
S. L. Breen ◽  
...  
Keyword(s):  
Star Formation ◽  
The Other ◽  
High Mass ◽  
Mass Star ◽  
Evolutionary Sequence ◽  
Physical Conditions ◽  
Other Information ◽  
Evolutionary Phase ◽  
The Common ◽  
Methanol Masers

AbstractInterstellar masers are unique probes of the environments in which they arise. In studies of high-mass star formation their primary function has been as signposts of these regions and they have been used as probes of the kinematics and physical conditions in only a few sources. With a few notable exceptions, we know relatively little about the evolutionary phase the different maser species trace, nor their location with respect to other star formation tracers. While detailed studies of a small number of maser regions can reveal much about them, other information can only be obtained through large, systematic searches. In particular, such surveys are vital in efforts to determine an evolutionary sequence for the common maser species, and there is growing evidence that methanol masers may trace an earlier phase than the other common maser species of OH and water.

scholarly journals Masers: High Resolution Probes of Massive Star Formation

2004 ◽  
Vol 221 ◽  
pp. 133-140 ◽  
Author(s):  
S P Ellingsen
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Massive Star ◽  
High Mass ◽  
Mass Star ◽  
Jigsaw Puzzle ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Evolutionary Phase ◽  
Methanol Masers

Astrophysical masers are one of the most readily detected signposts of high-mass star formation. Their presence indicates special conditions, probably indicative of a specific evolutionary phase. Masers also represent the ultimate high-resolution probe of star formation with the potential to reveal information on the kinematics and physical conditions within the region at milli-arcsecond resolution. To date this potential has largely remained unfulfilled, however, recent advances suggest that this will soon change.The key to unlocking the potential of masers lies in identifying where they fit within the star formation jigsaw puzzle. I will review recent high resolution observations of OH, water and methanol maser transitions and what they reveal. I also briefly discuss how multi-transition observations of OH and methanol masers are being used to constrain maser pumping models and through this estimate the physical conditions in the masing region.

Statistical analysis of the physical properties of the 6.7 GHz methanol maser features based on VLBI data

2017 ◽  
Vol 13 (S336) ◽  
pp. 321-322 ◽  
Author(s):  
R. Sarniak ◽  
M. Szymczak ◽  
A. Bartkiewicz
Keyword(s):  
Statistical Analysis ◽  
Star Formation ◽  
Physical Properties ◽  
Angular Resolution ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
Methanol Maser ◽  
Vlbi Data ◽  
Methanol Masers

AbstractMethanol masers observed at high angular resolution are useful tool to investigate the processes of high-mass star formation. Here, we present the results of statistical analysis of the 6.7 GHz methanol maser structures in 60 sources observed with the EVN. The parameters of the maser clouds and exciting stars were derived. There is evidence that the emission structures composed of larger number of maser clouds are formed in the vicinity of more luminous exciting stars.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals Ammonia observations towards the Aquila Rift cloud complex

2020 ◽  
Vol 643 ◽  
pp. A178
Author(s):  
Kadirya Tursun ◽  
Jarken Esimbek ◽  
Christian Henkel ◽  
Xindi Tang ◽  
Gang Wu ◽  
...  
Keyword(s):  
Star Formation ◽  
Dust Emission ◽  
Turbulent Energy ◽  
Gravitational Energy ◽  
High Mass ◽  
Kinetic Temperature ◽  
Mass Star ◽  
Dense Gas ◽  
Star Formation Region ◽  
Formation Region

We surveyed the Aquila Rift complex including the Serpens South and W 40 regions in the NH3 (1,1) and (2,2) transitions making use of the Nanshan 26-m telescope. Our observations cover an area of ~ 1.5° × 2.2° (11.4 pc × 16.7 pc). The kinetic temperatures of the dense gas in the Aquila Rift complex obtained from NH3 (2,2)/(1,1) ratios range from 8.9 to 35.0 K with an average of 15.3 ± 6.1 K (errors are standard deviations of the mean). Low gas temperatures are associated with Serpens South ranging from 8.9 to 16.8 K with an average of 12.3 ± 1.7 K, while dense gas in the W 40 region shows higher temperatures ranging from 17.7 to 35.0 K with an average of 25.1 ± 4.9 K. A comparison of kinetic temperatures derived from para-NH3 (2,2)/(1,1) against HiGal dust temperatures indicates that the gas and dust temperatures are in agreement in the low-mass-star formation region of Serpens South. In the high-mass-star formation region W 40, the measured gas kinetic temperatures are higher than those of the dust. The turbulent component of the velocity dispersion of NH3 (1,1) is found to be positively correlated with the gas kinetic temperature, which indicates that the dense gas may be heated by dissipation of turbulent energy. For the fractional total-NH3 (para+ortho) abundance obtained by a comparison with Herschel infrared continuum data representing dust emission, we find values from 0.1 ×10−8 to 2.1 ×10−7 with an average of 6.9 (±4.5) × 10−8. Serpens South also shows a fractional total-NH3 (para+ortho) abundance ranging from 0.2 ×10−8 to 2.1 ×10−7 with an average of 8.6 (±3.8) × 10−8. In W 40, values are lower, between 0.1 and 4.3 ×10−8 with an average of 1.6 (±1.4) × 10−8. Weak velocity gradients demonstrate that the rotational energy is a negligible fraction of the gravitational energy. In W 40, gas and dust temperatures are not strongly dependent on the projected distance to the recently formed massive stars. Overall, the morphology of the mapped region is ring-like, with strong emission at lower and weak emission at higher Galactic longitudes. However, the presence of a physical connection between the two parts remains questionable.

scholarly journals High Resolution Radio Continuum Observations of High Mass Star Formation Regions

2001 ◽  
Vol 205 ◽  
pp. 280-281
Author(s):  
S. Kurtz ◽  
P. Hofner ◽  
C. Vargas ◽  
W. Díaz-Merced
Keyword(s):  
Star Formation ◽  
Radio Continuum ◽  
High Mass ◽  
High Angular Resolution ◽  
Mass Star ◽  
High Quality ◽  
Very Large Array ◽  
Adverse Conditions ◽  
Star Formation Regions ◽  
Calibration Techniques

We present high angular resolution centimeter and millimeter continuum observations of several galactic massive star formation regions. Using calibration techniques pioneered at the Very Large Array, we are able to obtain high quality images even under adverse conditions of phase stability. Techniques such as these will be essential if future millimeter arrays are to obtain high quality and high precision images. We provide a current summary of our on-going survey, and present images and a brief discussion of several of the more intriguing sources.

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