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Sl Breen - One of the best experts on this subject based on the ideXlab platform.
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13ch3oh Masers associated with a transient phenomenon in a high mass young stellar object
The Astrophysical Journal, 2020Co-Authors: Xi Chen, S P Ellingsen, Sl Breen, M A Voronkov, A M Sobolev, Zhiqiang Shen, G C Macleod, J F Kaczmarek, Jiangshui Zhang, Zhi Yuan RenAbstract:We report the first detection of isotopic methanol (13CH3OH) maser emission in interstellar space. The emission was detected toward the high-mass young stellar object G358.93-0.03 during monitoring of a flare in the 6.7 GHz methanol (CH3OH) maser emission in this source. We find that the spectral and spatial distribution of the 13CH3OH Masers differs from the CH3OH Masers imaged at the same epoch, contrary to expectations from similarity of their pumping. This conclusively demonstrates that isotopic methanol Masers are bright under different physical conditions and suggests that they can provide additional, complementary information to the CH3OH Masers from the same source. We detect a rapid decay of the 13CH3OH maser lines suggesting that they are transient phenomena (masing for only a few months), likely associated with rapid changes in radiation field due to an accretion burst induced by massive disk fragmentation. Changes in the line flux density are faster than required to achieve equilibrium in the energy level populations, indicating that the pumping of these Masers is likely variable.
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Variability in extragalactic class I methanol Masers: new maser components towards NGC 4945 and NGC 253
'Oxford University Press (OUP)', 2020Co-Authors: Tp Mccarthy, S P Ellingsen, Sl Breen, Chen X, Qiao H-hAbstract:We have used the Australia Telescope Compact Array (ATCA) to make new observations of the 36.2-GHz (4−1 → 30E) methanol transition towards NGC 4945 and NGC 253. These observations have revealed the presence of new maser components towards these galaxies, and have provided the first clear evidence for variability in extragalactic class I methanol Masers. Alongside the new observations of NGC 4945 and NGC 253, we present the results of recent 36.2-GHz methanol maser searches towards 12 galaxies, placing upper limits on the emission from the 36.2-GHz class I transition and the 37.7-GHz (72 → 81E) class II maser line towards these sources. Flux density values for the 7-mm continuum emission towards these sources are also reported where applicable. A re-analysis of the published 36.2-GHz methanol observations of Arp 220 undertaken as part of the search revealed some issues with previous imaging procedures. The re-analysis, combined with non-detections in independent follow-up observations, suggests that there is no 36.2-GHz methanol emission towards Arp 220 stronger than 3.5 mJy in a 10 km s−1 channel (5σ upper limit)
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the 6 ghz multibeam maser survey ii statistical analysis and galactic distribution of 6668 mhz methanol Masers
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: J A Green, S P Ellingsen, Sl Breen, G A Fuller, N M Mccluregriffiths, M A Voronkov, A Avison, Kate BrooksAbstract:The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl Masers in the Galaxy to date. Observing the entire Galactic plane visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl Masers, to an rms sensitivity of 0.015 Jy km s−1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ∼1290 sources with flux densities above the survey 3σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability and range of source velocities. The data suggest that the weaker Masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol Masers. For the Galactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol Masers. We find that more luminous Masers have an evenly distributed wide range of velocity widths compared with less luminous Masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins.
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southern class i methanol Masers at 36 and 44 ghz
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: S P Ellingsen, Sl Breen, J A Green, M A Voronkov, J L CaswellAbstract:The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ɪɪ regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of Masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263 ± 15 mpc, irrespective of the transition. The class I Masers associated with OH Masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s −1 (uncertainties are 0.06 and 0.07 km s −1 for the 36- and 44-GHz Masers, respectively) with respect to the 6.7-GHz Masers. The standard deviation of the velocity distribution was found to be 3.65 ± 0.05 and 3.32 ± 0.07 km s −1 for the 36- and 44-GHz Masers, respectively. We also suggest a refined rest frequency value of 36 169.238 ± 0.011 MHz for the 4 −1 -3 0 E methanol transition.
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confirmation of the exclusive association between 6 7 ghz methanol Masers and high mass star formation regions
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Sl Breen, S P Ellingsen, J A Green, J L Caswell, Y Contreras, J A Stevens, J R Dawson, M A VoronkovAbstract:Recently, a comparison between the locations of 6.7-GHz methanol Masers and dust continuum emission has renewed speculation that these Masers can be associated with evolved stars. The implication of such a scenario would be profound, especially for the interpretation of large surveys for 6.7-GHz Masers, individual studies where high-mass star formation has been inferred from the presence of 6.7-GHz methanol Masers and for the pumping mechanisms of these Masers. We have investigated the two instances where 6.7-GHz methanol Masers have been explicitly suggested to be associated with evolved stars, and we find the first to be associated with a standard high-mass star formation region, and the second to be a spurious detection.We also find no evidence to suggest that the methanol maser action can be supported in the environments of evolved stars.We thereby confirm their exclusive association with high-mass star formation regions.
S P Ellingsen - One of the best experts on this subject based on the ideXlab platform.
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44 ghz methanol Masers observations toward 95 ghz methanol Masers
Astrophysical Journal Supplement Series, 2020Co-Authors: Wenjin Yang, S P Ellingsen, Yoon Kyung Choi, A M Sobolev, Xi ChenAbstract:We report a simultaneous 44 and 95 GHz class I methanol maser survey toward 144 sources from the 95 GHz class I methanol maser catalog. The observations were made with the three telescopes of the Korean very long baseline interferometry network operating in single-dish mode. The detection rates are 89% at 44 GHz and 77% at 95 GHz. There are 106 new discoveries at 44 GHz. Comparing the previous 95 GHz detections with new observations of the same transitions made using the Purple Mountain Observatory 13.7 m radio telescope shows no clear evidence of variability on a timescale of six years. Emission from the 44 and 95 GHz transitions shows strong correlations in peak velocity, peak flux density, and integrated flux density, indicating that they are likely cospatial. We found that the peak flux density ratio Spk,95/Spk,44 decreases as the 44 GHz peak flux density increases. We found that some class I methanol Masers in our sample might be associated with infrared dark clouds, while others are associated with H II regions, indicating that some sources occur at an early stage of high-mass star formation, while others are located toward more evolved sources.
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13ch3oh Masers associated with a transient phenomenon in a high mass young stellar object
The Astrophysical Journal, 2020Co-Authors: Xi Chen, S P Ellingsen, Sl Breen, M A Voronkov, A M Sobolev, Zhiqiang Shen, G C Macleod, J F Kaczmarek, Jiangshui Zhang, Zhi Yuan RenAbstract:We report the first detection of isotopic methanol (13CH3OH) maser emission in interstellar space. The emission was detected toward the high-mass young stellar object G358.93-0.03 during monitoring of a flare in the 6.7 GHz methanol (CH3OH) maser emission in this source. We find that the spectral and spatial distribution of the 13CH3OH Masers differs from the CH3OH Masers imaged at the same epoch, contrary to expectations from similarity of their pumping. This conclusively demonstrates that isotopic methanol Masers are bright under different physical conditions and suggests that they can provide additional, complementary information to the CH3OH Masers from the same source. We detect a rapid decay of the 13CH3OH maser lines suggesting that they are transient phenomena (masing for only a few months), likely associated with rapid changes in radiation field due to an accretion burst induced by massive disk fragmentation. Changes in the line flux density are faster than required to achieve equilibrium in the energy level populations, indicating that the pumping of these Masers is likely variable.
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Variability in extragalactic class I methanol Masers: new maser components towards NGC 4945 and NGC 253
'Oxford University Press (OUP)', 2020Co-Authors: Tp Mccarthy, S P Ellingsen, Sl Breen, Chen X, Qiao H-hAbstract:We have used the Australia Telescope Compact Array (ATCA) to make new observations of the 36.2-GHz (4−1 → 30E) methanol transition towards NGC 4945 and NGC 253. These observations have revealed the presence of new maser components towards these galaxies, and have provided the first clear evidence for variability in extragalactic class I methanol Masers. Alongside the new observations of NGC 4945 and NGC 253, we present the results of recent 36.2-GHz methanol maser searches towards 12 galaxies, placing upper limits on the emission from the 36.2-GHz class I transition and the 37.7-GHz (72 → 81E) class II maser line towards these sources. Flux density values for the 7-mm continuum emission towards these sources are also reported where applicable. A re-analysis of the published 36.2-GHz methanol observations of Arp 220 undertaken as part of the search revealed some issues with previous imaging procedures. The re-analysis, combined with non-detections in independent follow-up observations, suggests that there is no 36.2-GHz methanol emission towards Arp 220 stronger than 3.5 mJy in a 10 km s−1 channel (5σ upper limit)
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the 6 ghz multibeam maser survey ii statistical analysis and galactic distribution of 6668 mhz methanol Masers
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: J A Green, S P Ellingsen, Sl Breen, G A Fuller, N M Mccluregriffiths, M A Voronkov, A Avison, Kate BrooksAbstract:The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl Masers in the Galaxy to date. Observing the entire Galactic plane visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl Masers, to an rms sensitivity of 0.015 Jy km s−1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ∼1290 sources with flux densities above the survey 3σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability and range of source velocities. The data suggest that the weaker Masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol Masers. For the Galactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol Masers. We find that more luminous Masers have an evenly distributed wide range of velocity widths compared with less luminous Masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins.
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southern class i methanol Masers at 36 and 44 ghz
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: S P Ellingsen, Sl Breen, J A Green, M A Voronkov, J L CaswellAbstract:The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ɪɪ regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of Masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263 ± 15 mpc, irrespective of the transition. The class I Masers associated with OH Masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s −1 (uncertainties are 0.06 and 0.07 km s −1 for the 36- and 44-GHz Masers, respectively) with respect to the 6.7-GHz Masers. The standard deviation of the velocity distribution was found to be 3.65 ± 0.05 and 3.32 ± 0.07 km s −1 for the 36- and 44-GHz Masers, respectively. We also suggest a refined rest frequency value of 36 169.238 ± 0.011 MHz for the 4 −1 -3 0 E methanol transition.
M A Voronkov - One of the best experts on this subject based on the ideXlab platform.
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13ch3oh Masers associated with a transient phenomenon in a high mass young stellar object
The Astrophysical Journal, 2020Co-Authors: Xi Chen, S P Ellingsen, Sl Breen, M A Voronkov, A M Sobolev, Zhiqiang Shen, G C Macleod, J F Kaczmarek, Jiangshui Zhang, Zhi Yuan RenAbstract:We report the first detection of isotopic methanol (13CH3OH) maser emission in interstellar space. The emission was detected toward the high-mass young stellar object G358.93-0.03 during monitoring of a flare in the 6.7 GHz methanol (CH3OH) maser emission in this source. We find that the spectral and spatial distribution of the 13CH3OH Masers differs from the CH3OH Masers imaged at the same epoch, contrary to expectations from similarity of their pumping. This conclusively demonstrates that isotopic methanol Masers are bright under different physical conditions and suggests that they can provide additional, complementary information to the CH3OH Masers from the same source. We detect a rapid decay of the 13CH3OH maser lines suggesting that they are transient phenomena (masing for only a few months), likely associated with rapid changes in radiation field due to an accretion burst induced by massive disk fragmentation. Changes in the line flux density are faster than required to achieve equilibrium in the energy level populations, indicating that the pumping of these Masers is likely variable.
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the 6 ghz multibeam maser survey ii statistical analysis and galactic distribution of 6668 mhz methanol Masers
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: J A Green, S P Ellingsen, Sl Breen, G A Fuller, N M Mccluregriffiths, M A Voronkov, A Avison, Kate BrooksAbstract:The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl Masers in the Galaxy to date. Observing the entire Galactic plane visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl Masers, to an rms sensitivity of 0.015 Jy km s−1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ∼1290 sources with flux densities above the survey 3σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability and range of source velocities. The data suggest that the weaker Masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol Masers. For the Galactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol Masers. We find that more luminous Masers have an evenly distributed wide range of velocity widths compared with less luminous Masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins.
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southern class i methanol Masers at 36 and 44 ghz
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: S P Ellingsen, Sl Breen, J A Green, M A Voronkov, J L CaswellAbstract:The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ɪɪ regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of Masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263 ± 15 mpc, irrespective of the transition. The class I Masers associated with OH Masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s −1 (uncertainties are 0.06 and 0.07 km s −1 for the 36- and 44-GHz Masers, respectively) with respect to the 6.7-GHz Masers. The standard deviation of the velocity distribution was found to be 3.65 ± 0.05 and 3.32 ± 0.07 km s −1 for the 36- and 44-GHz Masers, respectively. We also suggest a refined rest frequency value of 36 169.238 ± 0.011 MHz for the 4 −1 -3 0 E methanol transition.
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confirmation of the exclusive association between 6 7 ghz methanol Masers and high mass star formation regions
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Sl Breen, S P Ellingsen, J A Green, J L Caswell, Y Contreras, J A Stevens, J R Dawson, M A VoronkovAbstract:Recently, a comparison between the locations of 6.7-GHz methanol Masers and dust continuum emission has renewed speculation that these Masers can be associated with evolved stars. The implication of such a scenario would be profound, especially for the interpretation of large surveys for 6.7-GHz Masers, individual studies where high-mass star formation has been inferred from the presence of 6.7-GHz methanol Masers and for the pumping mechanisms of these Masers. We have investigated the two instances where 6.7-GHz methanol Masers have been explicitly suggested to be associated with evolved stars, and we find the first to be associated with a standard high-mass star formation region, and the second to be a spurious detection.We also find no evidence to suggest that the methanol maser action can be supported in the environments of evolved stars.We thereby confirm their exclusive association with high-mass star formation regions.
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absolute positions of 6 7 ghz methanol Masers
arXiv: Astrophysics of Galaxies, 2009Co-Authors: M A Voronkov, A Brunthaler, A M Sobolev, J D Pandian, B Ritter, K M MentenAbstract:The ATCA, MERLIN and VLA interferometers were used to measure the absolute positions of 35 6.7 GHz methanol Masers to subarcsecond or higher accuracy. Our measurements represent essential preparatory data for Very Long Baseline Interferometry, which can provide accurate parallax and proper motion determinations of the star-forming regions harboring the Masers. Our data also allow associations to be established with infrared sources at different wavelengths. Our findings support the view that the 6.7 GHz Masers are associated with the earliest phases of high-mass star formation.
J L Caswell - One of the best experts on this subject based on the ideXlab platform.
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southern class i methanol Masers at 36 and 44 ghz
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: S P Ellingsen, Sl Breen, J A Green, M A Voronkov, J L CaswellAbstract:The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ɪɪ regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of Masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263 ± 15 mpc, irrespective of the transition. The class I Masers associated with OH Masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s −1 (uncertainties are 0.06 and 0.07 km s −1 for the 36- and 44-GHz Masers, respectively) with respect to the 6.7-GHz Masers. The standard deviation of the velocity distribution was found to be 3.65 ± 0.05 and 3.32 ± 0.07 km s −1 for the 36- and 44-GHz Masers, respectively. We also suggest a refined rest frequency value of 36 169.238 ± 0.011 MHz for the 4 −1 -3 0 E methanol transition.
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confirmation of the exclusive association between 6 7 ghz methanol Masers and high mass star formation regions
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Sl Breen, S P Ellingsen, J A Green, J L Caswell, Y Contreras, J A Stevens, J R Dawson, M A VoronkovAbstract:Recently, a comparison between the locations of 6.7-GHz methanol Masers and dust continuum emission has renewed speculation that these Masers can be associated with evolved stars. The implication of such a scenario would be profound, especially for the interpretation of large surveys for 6.7-GHz Masers, individual studies where high-mass star formation has been inferred from the presence of 6.7-GHz methanol Masers and for the pumping mechanisms of these Masers. We have investigated the two instances where 6.7-GHz methanol Masers have been explicitly suggested to be associated with evolved stars, and we find the first to be associated with a standard high-mass star formation region, and the second to be a spurious detection.We also find no evidence to suggest that the methanol maser action can be supported in the environments of evolved stars.We thereby confirm their exclusive association with high-mass star formation regions.
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water Masers accompanying oh and methanol Masers in star formation regions
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Sl Breen, S P Ellingsen, J L Caswell, Chris PhillipsAbstract:The Australia Telescope Compact Array has been used to measure positions with arcsecond accuracy for 379 Masers at the 22-GHz transition of water. The principal observation targets were 202 OH Masers of the variety associated with star formation regions (SFRs) in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol Masers were added. Many of the water Masers reported here are new discoveries and others had been reported, with position uncertainties exceeding 10 arcsec, from Parkes telescope single-dish observations many years ago. Variability in the Masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79 per cent (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water Masers coincide with a 1665-MHz ground-state OH maser counterpart. Our less uniform sample of methanol targets is not suitable for a full investigation of their association with water Masers, but we are able to explore differences between the velocities of peak emission from the three species and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. We also report the detection of ultracompact HII regions towards some of the sites. In combination with an investigation of correlations with IR sources from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.
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water Masers accompanying oh and methanol Masers in star formation regions
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Sl Breen, S P Ellingsen, J L Caswell, Chris PhillipsAbstract:The ATCA has been used to measure positions with arcsecond accuracy for 379 Masers at the 22-GHz transition of water. The principal observation targets were 202 OH Masers of the variety associated with star formation regions (SFR)s in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol Masers were added. Many of the water Masers reported here are new discoveries. Variability in the Masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79% (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water Masers coincide with a 1665-MHz ground-state OH maser counterpart. We explore the differences between the velocities of peak emission from the three species (OH, methanol and water), and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. In combination with an investigation of correlations with IR sources from the GLIMPSE catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.
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12 2 ghz methanol Masers towards 1 2 mm dust clumps quantifying high mass star formation evolutionary schemes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: S P Ellingsen, Sl Breen, J L Caswell, B E LewisAbstract:We report the results of a search for 12.2-GHz methanol maser emission, targeted towards 113 known 6.7-GHz methanol Masers associated with 1.2-mm dust continuum emission. Observations were carried out with the Australia Telescope National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20–25. We detect 68 12.2-GHz methanol Masers with flux densities in excess of our 5σ detection limit of 0.55 Jy, 30 of which are new discoveries. This equates to a detection rate of 60 per cent, similar to previous searches of comparable sensitivity. We have made a statistical investigation of the properties of the 1.2-mm dust clumps with and without associated 6.7-GHz methanol maser and find that 6.7-GHz methanol Masers are associated with 1.2-mm dust clumps with high-flux densities, masses and radii. We additionally find that 6.7-GHz methanol Masers with higher peak luminosities are associated with less dense 1.2-mm dust clumps than those 6.7-GHz methanol Masers with lower luminosities. We suggest that this indicates that more luminous 6.7-GHz methanol Masers are generally associated with a later evolutionary phase of massive star formation than less luminous 6.7-GHz methanol maser sources. Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without associated 12.2-GHz methanol maser emission shows that clumps associated with both class II methanol maser transitions are less dense than those with no associated 12.2-GHz methanol maser emission. Furthermore, 12.2-GHz methanol Masers are preferentially detected towards 6.7-GHz methanol Masers with associated OH Masers, suggesting that 12.2-GHz methanol Masers are associated with a later evolutionary phase of massive star formation. We have compared the colours of the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) point sources associated with the maser sources in the following two subgroups: 6.7-GHz methanol Masers with and without associated 12.2-GHz methanol Masers; and 6.7-GHz methanol Masers with high- and those with low-peak luminosities. There is little difference in the nature of the associated GLIMPSE point sources in any of these subgroups, and we propose that the Masers themselves are probably much more sensitive than mid-infrared data to evolutionary changes in the massive star formation regions that they are associated with. We present an evolutionary sequence for Masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time.
B E Lewis - One of the best experts on this subject based on the ideXlab platform.
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12 2 ghz methanol Masers towards 1 2 mm dust clumps quantifying high mass star formation evolutionary schemes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: S P Ellingsen, Sl Breen, J L Caswell, B E LewisAbstract:We report the results of a search for 12.2-GHz methanol maser emission, targeted towards 113 known 6.7-GHz methanol Masers associated with 1.2-mm dust continuum emission. Observations were carried out with the Australia Telescope National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20–25. We detect 68 12.2-GHz methanol Masers with flux densities in excess of our 5σ detection limit of 0.55 Jy, 30 of which are new discoveries. This equates to a detection rate of 60 per cent, similar to previous searches of comparable sensitivity. We have made a statistical investigation of the properties of the 1.2-mm dust clumps with and without associated 6.7-GHz methanol maser and find that 6.7-GHz methanol Masers are associated with 1.2-mm dust clumps with high-flux densities, masses and radii. We additionally find that 6.7-GHz methanol Masers with higher peak luminosities are associated with less dense 1.2-mm dust clumps than those 6.7-GHz methanol Masers with lower luminosities. We suggest that this indicates that more luminous 6.7-GHz methanol Masers are generally associated with a later evolutionary phase of massive star formation than less luminous 6.7-GHz methanol maser sources. Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without associated 12.2-GHz methanol maser emission shows that clumps associated with both class II methanol maser transitions are less dense than those with no associated 12.2-GHz methanol maser emission. Furthermore, 12.2-GHz methanol Masers are preferentially detected towards 6.7-GHz methanol Masers with associated OH Masers, suggesting that 12.2-GHz methanol Masers are associated with a later evolutionary phase of massive star formation. We have compared the colours of the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) point sources associated with the maser sources in the following two subgroups: 6.7-GHz methanol Masers with and without associated 12.2-GHz methanol Masers; and 6.7-GHz methanol Masers with high- and those with low-peak luminosities. There is little difference in the nature of the associated GLIMPSE point sources in any of these subgroups, and we propose that the Masers themselves are probably much more sensitive than mid-infrared data to evolutionary changes in the massive star formation regions that they are associated with. We present an evolutionary sequence for Masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time.
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12 2 ghz methanol Masers associated with 1 2 mm dust clumps quantifying high mass star formation evolutionary schemes
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Sl Breen, S P Ellingsen, J L Caswell, B E LewisAbstract:We report the results of a search for 12.2-GHz methanol maser emission, targeted towards 113 known 6.7-GHz methanol Masers associated with 1.2-mm dust continuum emission. Observations were carried out with the Australia Telescope National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20 - 25. We detect 68 12.2-GHz methanol Masers with flux densities in excess of our 5-sigma detection limit of 0.55 Jy, 30 of which are new discoveries. This equates to a detection rate of 60 per cent, similar to previous searches of comparable sensitivity. We have made a statistical investigation of the properties of the 1.2-mm dust clumps with and without associated 6.7-GHz methanol maser and find that 6.7-GHz methanol Masers are associated with 1.2-mm dust clumps with high flux densities, masses and radii. We additionally find that 6.7-GHz methanol Masers with higher peak luminosities are associated with less dense 1.2-mm dust clumps than those 6.7-GHz methanol Masers with lower luminosities. We suggest that this indicates that more luminous 6.7-GHz methanol Masers are generally associated with a later evolutionary phase of massive star formation than less luminous 6.7-GHz methanol maser sources. Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without associated 12.2-GHz methanol maser emission shows that clumps associated with both class II methanol maser transitions are less dense than those with no associated 12.2-GHz methanol maser emission; suggesting that 12.2-GHz methanol Masers are associated with a later evolutionary phase of massive star formation. We present an evolutionary sequence for Masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time.
