scholarly journals A 12.2 GHz Methanol Maser Survey toward the 6.7 GHz Counterparts Associated with/without UC H ii Regions

2022 ◽  
Vol 258 (1) ◽  
pp. 19
Author(s):  
Shi-Min Song ◽  
Xi Chen ◽  
Zhi-Qiang Shen ◽  
Bin Li ◽  
Kai Yang ◽  
...  
Keyword(s):  
Detection Rate ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Methanol Maser ◽  
Physical Environments ◽  
Methanol Masers

Abstract We report a new survey of the 12.2 GHz Class II methanol masers toward a sample of 367 sources with the 6.7 GHz methanol masers conducted with the Shanghai 65 m Tianma Radio Telescope. This sample has been previously made with observations of the radio continuum emission of UC H ii regions by the VLA. A total of 176 sources were detected with the 12.2 GHz methanol maser, with a detection rate of 48%, including 8 new detections. A lower detection rate (<10%) was determined toward the sources in the Galactic longitude ranges of 60°–180°, revealing that the physical environments from those sources in the Local arm or the tails of Galactic arms do not easily excite the 12.2 GHz masers. In addition, two detections of highly excited-state OH masers at the 13.4 GHz transition were made, one of which is a new detection. Compared to previous surveys, one-third of the detected 12.2 GHz masers show considerable flux variations, implying the possible changes of their physical environments associated with variable radiation fields from their host high-mass young stellar objects. A positive log–log correlation is found between the luminosities of the 6.7 and 12.2 GHz masers in our observed sample, suggesting that both the transition masers have similar excitation conditions. The statistical analysis for the relationships between the methanol maser luminosity and UC H ii region spatial size indicates that the maser luminosities of both the 6.7 and 12.2 GHz transitions have a decreasing trend with the spatial sizes of the associated UC H ii regions, indicating that the Class II methanol masers might fade away with the H ii region evolution.

scholarly journals Birthplace of 6.7 GHz methanol masers

2012 ◽  
Vol 8 (S292) ◽  
pp. 42-42
Author(s):  
Cong-Gui Gan ◽  
Xi Chen ◽  
Zhi-Qiang Shen
Keyword(s):  
Magnetic Field ◽  
Major Axis ◽  
Field Vector ◽  
Magnetic Field Vector ◽  
Young Stellar Objects ◽  
High Mass ◽  
Stellar Objects ◽  
Methanol Maser ◽  
Vlbi Observations ◽  
Methanol Masers

AbstractWe performed polarization sensitive VLBI observations of 6.7 GHz methanol masers toward high-mass young stellar objects with clear outflow seen from Spitzer IRAC images in the 4.5 μm band (i.e. EGOs, see Cyganowski et al. 2008) with the EVN to investigate the birthplace of the masers. By comparing direction of the major axis of methanol maser distributions with directions of higher resolution outflow and magnetic field vector, we suggest that the methanol masers toward source G28.83-0.25 may arise from surrounding disk.

scholarly journals Giant burst of methanol maser in S255IR-NIRS3

2018 ◽  
Vol 617 ◽  
pp. A80 ◽  
Author(s):  
M. Szymczak ◽  
M. Olech ◽  
P. Wolak ◽  
E. Gérard ◽  
A. Bartkiewicz
Keyword(s):  
Sampling Interval ◽  
Young Stellar Objects ◽  
High Mass ◽  
Stellar Objects ◽  
Maser Emission ◽  
Methanol Maser ◽  
Star Evolution ◽  
Average Sampling ◽  
Methanol Masers ◽  
Observational Signature

Context. High-mass young stellar objects (HMYSOs) can undergo accretion episodes that strongly affect the star evolution, the dynamics of the disk, and its chemical evolution. Recently reported extraordinary bursts in the methanol maser emission may be the observational signature of accretion events in deeply embedded HMYSOs. Aims. We analyze the light curve of 6.7 GHz methanol masers in S255IR-NIRS3 during the 2015–2016 burst. Methods. 8.5-yr monitoring data with an average sampling interval of 5 days were obtained with the Torun 32 m radio telescope. Archival data were added, extending the time series to ~27 yr. Results. The maser emission showed moderate (25–30%) variability on timescales of months to years over ~23 yr since its discovery. The main burst was preceded by a 1 yr increase of the total flux density by a factor of 2.5, then it grew by a factor of 10 over ~0.4 yr and declined by a factor of 8 during the consecutive 2.4 yr. The peak maser luminosity was a factor of 24.5 higher than the pre-burst quiescent value. The light curves of individual features showed considerable diversity but indicated a general trend of suppression of the maser emission at blueshifted (<4.7 km s−1) velocities when the redshifted emission rapidly grew and new emission features appeared at velocities >5.8 km s−1. This new emission provided a contribution of about 80% to the maser luminosity around the peak of the burst. The duration of the burst at the extreme redshifted velocities of 7.1–8.7 km s−1 was from 0.9 to 1.9 yr, and its lower limit for the other features was ~3.9 yr. Conclusions. The onset of the maser burst exactly coincides with that of the infrared burst estimated from the motion of the light echo. This strongly supports the radiative pumping scheme of the maser transition. The growth of the maser luminosity is the result of an increasing volume of gas where the maser inversion is achieved.

Preliminary Results of a Survey of Ultracompact H II Regions

1995 ◽  
Vol 12 (2) ◽  
pp. 186-189 ◽  
Author(s):  
A. J. Walsh ◽  
A. R. Hyland ◽  
G. Robinson ◽  
T. L. Bourke ◽  
S. D. James
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Mass Star ◽  
Methanol Maser ◽  
Preliminary Results ◽  
Selection Of

AbstractUltracompact H II regions are small, dense regions of ionised gas surrounding high-mass stars which are still embedded in their natal molecular clouds. A survey of such regions has been commenced in an attempt to improve our understanding of the processes of high-mass star formation. The initial stages of the survey have involved selection of likely candidates from the IRAS Point Source Catalogue, correlation with radio continuum emission at 4·85 GHz and subsequent observations of methanol maser emission at 6·668 GHz. Preliminary results of the methanol maser survey are given.

scholarly journals 44-GHz class I methanol maser survey towards 6.7-GHz class II methanol masers

2012 ◽  
Vol 8 (S287) ◽  
pp. 284-285 ◽  
Author(s):  
Do-Young Byun ◽  
Kee-Tae Kim ◽  
Jae-Han Bae
Keyword(s):  
Class Ii ◽  
Class I ◽  
Young Stellar Objects ◽  
High Mass ◽  
Radio Telescopes ◽  
Stellar Objects ◽  
Methanol Maser ◽  
Peak Flux ◽  
Methanol Masers ◽  
Water Maser

AbstractThe Class II 6.7-GHz methanol maser is a tracer of high mass young stellar objects. We present results of a 44-GHz class I methanol maser and 22-GHz water maser survey using the KVN (Korean VLBI Network) 21-m single dish radio telescopes towards 284 6.7-GHz maser sites. Class I methanol maser and water maser emission is detected towards 116 (41%) and 136 (48%) sources, respectively. About 50 sources have a peak flux density higher than 10 Jy at 44-GHz. They are candidates for VLBI studies using the KVN.

Probing GLIMPSE Extended Green Objects (EGOs) with hydroxyl masers

2020 ◽  
Vol 499 (3) ◽  
pp. 3961-3975
Author(s):  
O S Bayandina ◽  
P Colom ◽  
S E Kurtz ◽  
G M Rudnitskij ◽  
N N Shakhvorostova ◽  
...  
Keyword(s):  
Detection Rate ◽  
Infrared Emission ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Maser Emission ◽  
Very Large Array ◽  
Methanol Masers ◽  
Cent Detection

ABSTRACT We present a study of 18 cm OH maser emission toward 20 high-mass young stellar object outflow candidates (Extended Green Objects, EGOs) identified from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). All four OH ground state lines at 1612, 1665, 1667, and 1720 MHz, together with 20-cm continuum emission, were observed with the Karl G. Jansky Very Large Array C-configuration. Follow-up polarimetric single-dish observations with the Nançay radio telescope were performed for the same OH transitions, except 1612 MHz. OH maser emission is found to be an uncommon feature of the sample, with a 50 per cent detection rate for the entire sample and a ∼44 per cent detection rate for the ‘likely’ EGOs. No 20-cm continuum emission is detected toward any of the sources. In most cases, the detected OH maser emission arises in vicinity to compact central sources; OH masers coexist with the 6.7 GHz methanol masers, but are found in more diffuse and extended halo-shaped regions of several thousand astronomical units in size. Comparing EGO samples with OH maser detection and non-detection, EGOs showing OH maser emission tend to have lower dust clump masses, but higher 24 and 4.5 μm flux densities. Thus, OH maser emission might be an indicator of more evolved EGOs, since strong compact mid-infrared emission in the absence of compact radio continuum emission is thought to be associated with the later stage of massive star formation.

scholarly journals Principal component analysis tomography in near-infrared integral field spectroscopy of young stellar objects – I. Revisiting the high-mass protostar W33A

2021 ◽  
Vol 503 (1) ◽  
pp. 270-291
Author(s):  
F Navarete ◽  
A Damineli ◽  
J E Steiner ◽  
R D Blum
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Rotation Axis ◽  
Principal Component ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
Rotating Disc ◽  
Stellar Objects ◽  
K Band

ABSTRACT W33A is a well-known example of a high-mass young stellar object showing evidence of a circumstellar disc. We revisited the K-band NIFS/Gemini North observations of the W33A protostar using principal components analysis tomography and additional post-processing routines. Our results indicate the presence of a compact rotating disc based on the kinematics of the CO absorption features. The position–velocity diagram shows that the disc exhibits a rotation curve with velocities that rapidly decrease for radii larger than 0.1 arcsec (∼250 au) from the central source, suggesting a structure about four times more compact than previously reported. We derived a dynamical mass of 10.0$^{+4.1}_{-2.2}$ $\rm {M}_\odot$ for the ‘disc + protostar’ system, about ∼33 per cent smaller than previously reported, but still compatible with high-mass protostar status. A relatively compact H2 wind was identified at the base of the large-scale outflow of W33A, with a mean visual extinction of ∼63 mag. By taking advantage of supplementary near-infrared maps, we identified at least two other point-like objects driving extended structures in the vicinity of W33A, suggesting that multiple active protostars are located within the cloud. The closest object (Source B) was also identified in the NIFS field of view as a faint point-like object at a projected distance of ∼7000 au from W33A, powering extended K-band continuum emission detected in the same field. Another source (Source C) is driving a bipolar $\rm {H}_2$ jet aligned perpendicular to the rotation axis of W33A.

Radio continuum emission from young stellar objects in L1641

1990 ◽  
Vol 362 ◽  
pp. 274 ◽  
Author(s):  
James A. Morgan ◽  
Ronald L. Snell ◽  
Karen M. Strom
Keyword(s):  
Radio Continuum ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Stellar Objects

scholarly journals A timeline for massive star-forming regions via combined observation of o-H2D+ and N2D+

2019 ◽  
Vol 621 ◽  
pp. L7 ◽  
Author(s):  
A. Giannetti ◽  
S. Bovino ◽  
P. Caselli ◽  
S. Leurini ◽  
D. R. G. Schleicher ◽  
...  
Keyword(s):  
Free Fall ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
State Transitions ◽  
Temperature Sensitive ◽  
Evolutionary Stage ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions

Context. In cold and dense gas prior to the formation of young stellar objects, heavy molecular species (including CO) are accreted onto dust grains. Under these conditions H3+ and its deuterated isotopologues become more abundant, enhancing the deuterium fraction of molecules such as N2H+ that are formed via ion-neutral reactions. Because this process is extremely temperature sensitive, the abundance of these species is likely linked to the evolutionary stage of the source. Aims. We investigate how the abundances of o-H2D+ and N2D+ vary with evolution in high-mass clumps. Methods. We observed with APEX the ground-state transitions of o-H2D+ near 372 GHz, and N2D+(3–2) near 231 GHz for three massive clumps in different evolutionary stages. The sources were selected within the G351.77–0.51 complex to minimise the variation of initial chemical conditions, and to remove distance effects. We modelled their dust continuum emission to estimate their physical properties, and also modelled their spectra under the assumption of local thermodynamic equilibrium to calculate beam-averaged abundances. Results. We find an anticorrelation between the abundance of o-H2D+ and that of N2D+, with the former decreasing and the latter increasing with evolution. With the new observations we are also able to provide a qualitative upper limit to the age of the youngest clump of about 105 yr, comparable to its current free-fall time. Conclusions. We can explain the evolution of the two tracers with simple considerations on the chemical formation paths, depletion of heavy elements, and evaporation from the grains. We therefore propose that the joint observation and the relative abundance of o-H2D+ and N2D+ can act as an efficient tracer of the evolutionary stages of the star-formation process.

scholarly journals Infrared variability, maser activity, and accretion of massive young stellar objects

2017 ◽  
Vol 13 (S336) ◽  
pp. 37-40 ◽  
Author(s):  
Bringfried Stecklum ◽  
Alessio Caratti o Garatti ◽  
Klaus Hodapp ◽  
Hendrik Linz ◽  
Luca Moscadelli ◽  
...  
Keyword(s):  
Light Curve ◽  
Young Stellar Objects ◽  
High Mass ◽  
Periodic Activity ◽  
Intermediate Mass ◽  
Stellar Objects ◽  
Methanol Masers ◽  
Water Masers ◽  
First Time ◽  
Ir Light

AbstractMethanol and water masers indicate young stellar objects. They often exhibit flares, and a fraction shows periodic activity. Several mechanisms might explain this behavior but the lack of concurrent infrared (IR) data complicates the identification of its cause. Recently, 6.7 GHz methanol maser flares were observed, triggered by accretion bursts of high-mass YSOs which confirmed the IR-pumping of these masers. This suggests that regular IR changes might lead to maser periodicity. Hence, we scrutinized space-based IR imaging of YSOs associated with periodic methanol masers. We succeeded to extract the IR light curve from NEOWISE data for the intermediate mass YSO G107.298+5.639. Thus, for the first time a relationship between the maser and IR variability could be established. While the IR light curve shows the same period of ~34.6 days as the masers, its shape is distinct from that of the maser flares. Possible reasons for the IR periodicity are discussed.

scholarly journals Dark Supernova Remnants Revealed by CO-Line Bubbles in the W43 Molecular Complex along the 4-kpc Galactic Arm

Galaxies ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 13
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Molecular Clouds ◽  
Supernova Remnants ◽  
Dust Emission ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Giant Molecular Clouds ◽  
Turbulent Structures ◽  
Stellar Objects ◽  
Receiver System

Fine structure of the density distribution in giant molecular clouds (GMCs) around W43 (G31+00+90 km s−1at ∼5.5 kpc) was analyzed using the FUGIN* CO-line survey at high-angular (20”∼0.5 pc) and velocity (1.3 km s−1) resolutions (*Four-receiver-system Unbiased Galactic Imaging survey with the Nobeyama 45-m telescope). The GMCs show highly turbulent structures, and the eddies are found to exhibit spherical bubble morphology appearing in narrow ranges of velocity channels. The bubbles are dark in radio continuum emission, unlike usual supernova remnants (SNR) or HII regions, and in infrared dust emission, unlike molecular bubbles around young stellar objects. The CO bubbles are interpreted as due to fully evolved buried SNRs in molecular clouds after rapid exhaustion of the released energy in dense molecular clouds. Then, the CO bubbles may be a direct evidence for exciting and maintaining the turbulence in GMCs by SN origin. Search for CO bubbles as “dark SNRs” (dSNR) will have implication to estimate the supernova rate more accurately, and hence the star formation activity in the Milky Way.

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