scholarly journals Methanol Masers—Are They in Circumstellar Disks?

1998 ◽  
Vol 164 ◽  
pp. 377-378
Author(s):  
R. P. Norris ◽  
C. J. Phillips ◽  
S. P. Ellingsen
Keyword(s):  
Recent Work ◽  
Circumstellar Disks ◽  
Methanol Maser ◽  
H Ii Region ◽  
Methanol Masers ◽  
Water Masers

AbstractSince the discovery of the 12.2 and 6.7 GHz methanol maser lines, these masers have been studied in great detail. Even in the earliest studies, it appeared that in some fraction of the sources, the maser spots were arranged in lines. This contrasts with the well-studied OH and water masers, in which the masers tended to be clustered almost randomly around a compact H ɪɪ region. Here I describe recent work to investigate the hypothesis that these lines represent edge-on circumstellar disks.

scholarly journals G23.657−0.127, what can we learn from a perfect methanol maser source?

2007 ◽  
Vol 3 (S242) ◽  
pp. 190-191
Author(s):  
Anna Bartkiewicz ◽  
Huib Jan van Langevelde ◽  
Marian Szymczak ◽  
Andreas Brunthaler
Keyword(s):  
Massive Stars ◽  
Ring Structure ◽  
Rotating Disks ◽  
Central Source ◽  
Methanol Maser ◽  
Early Results ◽  
H Ii Region ◽  
Methanol Masers

AbstractIn the course of following up compact methanol masers at 6.7 GHz which were found in the Torun blind survey (Szymczak et al. 2002), we discovered a ring structure in the source G23.657−00.127. This source provides interesting insights into whether methanol masers arise in rotating disks around massive stars, in their outflows, or behind shocks. By monitoring the 12.2 GHz masers, which fortunately follow the same structure, we hope to resolve the kinematics of the ring. Moreover, the symmetry of the source points to the existence of a central source. Early results on the nature of this source indicate the existence of a hyper–compact H II region.

scholarly journals Masers in G34.3+0.2: What more can 6.7-GHz methanol masers tell us?

2002 ◽  
Vol 206 ◽  
pp. 159-162 ◽  
Author(s):  
Jiyune Yi ◽  
Chris J. Phillips ◽  
Roy S. Booth
Keyword(s):  
Massive Star ◽  
Continuum Emission ◽  
Evolutionary Stage ◽  
Hii Region ◽  
Methanol Maser ◽  
Methanol Masers ◽  
Water Masers

We present results of 6.7 GHz methanol maser observations using the European VLBI Network (EVN) toward the G34.3+0.2 complex, which contains a prototypical cometary HII region and a dust enshrouded, probably emerging massive star, G34.24+0.13. We have investigated the methanol maser distribution in both objects and compared it with the OH and water masers in the main HII region. The masers in G34.24+0.13 lie on top of the 1.3 mm continuum emission showing that methanol masers are present, even at this early evolutionary stage.

scholarly journals 0″.4 BIMA Array Mapping of the 107 GHz Methanol Maser in W3(OH)

1998 ◽  
Vol 164 ◽  
pp. 379-380
Author(s):  
V. I. Slysh ◽  
I. E. Val’tts ◽  
S. V. Kalenskii ◽  
G. M. Larionov ◽  
L. G. Mundy
Keyword(s):  
Brightness Temperature ◽  
Lower Limit ◽  
Angular Resolution ◽  
Class Ii ◽  
Methanol Maser ◽  
H Ii Region ◽  
Methanol Masers

AbstractUsing A-configuration of the BIMA-array with 0″.4 angular resolution maps were obtained of the 107 GHz methanol line in W3(OH). The 107 GHz masers have their counterparts in another methanol transition at 6.7 GHz. The strongest maser spots are unresolved with the BIMA-array and are less than , which corresponds to the lower limit of the brightness temperature 5×105 K. A model of Class II methanol masers emitted in the extended atmosphere of icy planets orbiting around the O-star which excites H ɪɪ region is proposed.

Class I Methanol Maser Emission in NGC 4945

2017 ◽  
Vol 13 (S336) ◽  
pp. 105-108
Author(s):  
Tiege P. McCarthy ◽  
Simon P. Ellingsen ◽  
Xi Chen ◽  
Shari L. Breen ◽  
Maxim A. Voronkov ◽  
...  
Keyword(s):  
Large Scale ◽  
Class I ◽  
Molecular Gas ◽  
Low Velocity ◽  
Extragalactic Source ◽  
Maser Emission ◽  
Methanol Maser ◽  
Methanol Masers

AbstractWe have detected maser emission from the 36.2 GHz (4−1 → 30E) methanol transition towards NGC 4945. This emission has been observed in two separate epochs and is approximately five orders of magnitude more luminous than typical emission from this transition within our Galaxy. NGC 4945 is only the fourth extragalactic source observed hosting class I methanol maser emission. Extragalactic class I methanol masers do not appear to be simply highly-luminous variants of their galactic counterparts and instead appear to trace large-scale regions where low-velocity shocks are present in molecular gas.

14 years of 6.7 GHz periodic methanol maser observations towards G188.95+0.89

2019 ◽  
Vol 15 (S356) ◽  
pp. 393-394
Author(s):  
Martin M. Mutie ◽  
Paul Baki ◽  
James O. Chibueze ◽  
Khadija El Bouchefry
Keyword(s):  
Radio Telescope ◽  
Exponential Decay ◽  
Hii Regions ◽  
Monitoring Period ◽  
Methanol Maser ◽  
Spectral Components ◽  
Methanol Masers ◽  
Compact Hii Regions

AbstractWe report the results of 14 years of monitoring of G188.95+0.89 periodic 6.7 GHz methanol masers using the Hartebeesthoek 26-m radio telescope. G188.95+0.89 (S252, AFGL5180) is a radio-quiet methanol maser site that is often interpreted as precursors of ultra-compact HII regions or massive protostar sites. At least five bright spectral components were identified. The maser feature at 11.36 km s-1 was found to experience an exponential decay during the monitoring period. The millimetre continuum reveals two cores associated with the source.

Synchronized periodic maser flares of multiple OH and CH3OH lines in G323.459–0.079

2021 ◽  
Vol 502 (4) ◽  
pp. 5658-5667
Author(s):  
G C MacLeod ◽  
Derck P Smits ◽  
J A Green ◽  
S P van den Heever
Keyword(s):  
Magnetic Field ◽  
Excited State ◽  
Central Region ◽  
Time Lags ◽  
Field Reversal ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Upper Limit ◽  
Methanol Masers ◽  
Magnetic Field Reversal

ABSTRACT The first confirmed periodically varying 6.031 and 6.035 GHz hydroxyl masers are reported here. They vary contemporaneously with the 6.7 GHz methanol masers in G323.459–0.079. The 1.665 GHz hydroxyl and 12.2  GHz methanol masers associated with G323.459–0.079 are also periodic. Evidence for periodicity is seen in all features in all transitions save a single 1.665 GHz hydroxyl maser feature. Historical excited-state hydroxyl maser observations set a stricter upper limit on the epoch in which a significant accretion event occurred. The associated burst in 6.7 GHz methanol maser activity has subsided significantly while the hydroxyl transitions are brightening possibly the result of changing physical conditions in the masing cloudlets. Time lags in methanol are confirmed and may be the result of the periodic flaring propagating outward from the central region of maser activity. A possible magnetic field reversal occurred during the accretion event.

scholarly journals Millimetre wavelength methanol masers survey towards massive star forming regions

2007 ◽  
Vol 3 (S242) ◽  
pp. 234-235
Author(s):  
T. Umemoto ◽  
N. Mochizuki ◽  
K. M. Shibata ◽  
D.-G. Roh ◽  
H.-S. Chung
Keyword(s):  
Detection Rate ◽  
Massive Star ◽  
Molecular Line ◽  
Maser Emission ◽  
Star Forming ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Methanol Masers ◽  
Maser Sources

AbstractWe present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above −25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

scholarly journals The evolutionary status of protostellar clumps hosting class II methanol masers

2020 ◽  
Vol 493 (2) ◽  
pp. 2015-2041 ◽  
Author(s):  
B M Jones ◽  
G A Fuller ◽  
S L Breen ◽  
A Avison ◽  
J A Green ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Dust Emission ◽  
Principal Component ◽  
Far Infrared ◽  
Class Ii ◽  
Young Stellar Objects ◽  
Galactic Centre ◽  
Evolutionary Status ◽  
Methanol Maser ◽  
Methanol Masers

ABSTRACT The Methanol MultiBeam survey (MMB) provides the most complete sample of Galactic massive young stellar objects (MYSOs) hosting 6.7 GHz class II methanol masers. We characterize the properties of these maser sources using dust emission detected by the Herschel Infrared Galactic Plane Survey (Hi-GAL) to assess their evolutionary state. Associating 731 (73 per cent) of MMB sources with compact emission at four Hi-GAL wavelengths, we derive clump properties and define the requirements of an MYSO to host a 6.7 GHz maser. The median far-infrared (FIR) mass and luminosity are 630 M⊙ and 2500 L⊙ for sources on the near side of Galactic centre and 3200 M⊙ and 10000 L⊙ for more distant sources. The median luminosity-to-mass ratio is similar for both at ∼4.2 L⊙  M⊙−1. We identify an apparent minimum 70 μm luminosity required to sustain a methanol maser of a given luminosity (with $L_{70} \propto L_{6.7}\, ^{0.6}$). The maser host clumps have higher mass and higher FIR luminosities than the general Galactic population of protostellar MYSOs. Using principal component analysis, we find 896 protostellar clumps satisfy the requirements to host a methanol maser but lack a detection in the MMB. Finding a 70 μm flux density deficiency in these objects, we favour the scenario in which these objects are evolved beyond the age where a luminous 6.7 GHz maser can be sustained. Finally, segregation by association with secondary maser species identifies evolutionary differences within the population of 6.7GHz sources.

scholarly journals A blind survey of the 6.7 GHz methanol maser line

2002 ◽  
Vol 206 ◽  
pp. 143-146
Author(s):  
Marian Szymczak ◽  
Andrzej J. Kus ◽  
Grzegorz Hrynek
Keyword(s):  
Grid Point ◽  
Hii Regions ◽  
Triangular Grid ◽  
Average Sensitivity ◽  
Grid Pattern ◽  
Methanol Maser ◽  
Peak Flux ◽  
Maser Line ◽  
Methanol Masers ◽  
Ultracompact Hii

A blind survey for 6.7GHz methanol maser emission has been made with the 32 m Toruń radio telescope. The survey consists of 4,800 spectra on an equilateral triangular grid pattern with each grid point separated by 4.4 covering a field of ∼21 deg2 at galactic longitudes 20° to 40° and galactic latitudes ±0°52. The average sensitivity was 1.6 Jy and the spectral resolution was 0.04kms−1. A total of 99 sources were detected, 28 of which were not found during previous searches of IRAS-selected ultracompact HII regions. The peak flux density of new detections is usually lower than 30 Jy. About half of the methanol masers have no IRAS counterparts within a radius of 2. The nature of these sources is unclear.

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