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M J Reid - One of the best experts on this subject based on the ideXlab platform.
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the environment of the strongest galactic methanol Maser
The Astrophysical Journal, 2015Co-Authors: A Sanna, S P Ellingsen, A Brunthaler, M J Reid, K M Menten, L Moscadelli, R Cesaroni, Carlos Carrascogonzalez, V KrishnanAbstract:The high-mass star-forming site G009.62+00.20 E hosts the 6.7 GHz methanol Maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last 10 yr. We performed high-resolution astrometric measurements of the CH3OH, H2O, and OH Maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH3OH Maser cloudlets are distributed along two north–south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH3OH Maser transitions. We suggest that the periodic Maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest Masers. We also report the discovery of an elliptical distribution of CH3OH Maser emission in the region of periodic variability.
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the environment of the strongest galactic methanol Maser
arXiv: Astrophysics of Galaxies, 2015Co-Authors: A Sanna, S P Ellingsen, A Brunthaler, M J Reid, K M Menten, L Moscadelli, R Cesaroni, Carlos Carrascogonzalez, V KrishnanAbstract:The high-mass star-forming site G009.62+00.20E hosts the 6.7 GHz methanol Maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last ten years. We performed high-resolution astrometric measurements of the CH3OH, H2O, and OH Maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH3OH Maser cloudlets are distributed along two north-south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH3OH Maser transitions. We suggest that the periodic Maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest Masers. We also report about the discovery of an elliptical distribution of CH3OH Maser emission in the region of periodic variability.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
Astronomy and Astrophysics, 2011Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:Context. Both 22 GHz water and 6.7 GHz methanol Masers are usually interpreted as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments in which they occur. Aims. We attempt to derive accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission mapped earlier with Very Long Baseline Interferometry. Methods. We searched for 22 GHz water Masers in 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Results. Water Maser clusters are detected towards 27 sites leading to the identification of 15 new sources. The detection rate of water Maser emission associated with methanol sources is as high as 71%. In a large number of objects (18/21), the structure of water Maser is well aligned with that of the extended emission at 4.5 μm confirming the origin of water emission in outflows. The sources of methanol emission with ring-like morphologies, which likely trace a circumstellar disc/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. Conclusions. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario where 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appear to trace outflows. The two types of associations may be related to different evolutionary phases.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
arXiv: Astrophysics of Galaxies, 2010Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:22 GHz water and 6.7 GHz methanol Masers are usually thought as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments they occur in. The aim was to obtain accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission recently mapped with Very Long Baseline Interferometry. A sample of 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Water Maser clusters were detected towards 27 sites finding 15 new sources. The detection rate of water Maser emission associated with methanol sources was as high as 71%. In a large number of objects (18/21) the structure of water Maser is well aligned with that of the extended emission at 4.5 $\mu$m confirming the origin of water emission from outflows. The sources with methanol emission with ring-like morphologies, which likely trace a circumstellar disk/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario that 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appears to trace outflows. The two types of associations might be related to different evolutionary phases.
A Brunthaler - One of the best experts on this subject based on the ideXlab platform.
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the environment of the strongest galactic methanol Maser
The Astrophysical Journal, 2015Co-Authors: A Sanna, S P Ellingsen, A Brunthaler, M J Reid, K M Menten, L Moscadelli, R Cesaroni, Carlos Carrascogonzalez, V KrishnanAbstract:The high-mass star-forming site G009.62+00.20 E hosts the 6.7 GHz methanol Maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last 10 yr. We performed high-resolution astrometric measurements of the CH3OH, H2O, and OH Maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH3OH Maser cloudlets are distributed along two north–south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH3OH Maser transitions. We suggest that the periodic Maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest Masers. We also report the discovery of an elliptical distribution of CH3OH Maser emission in the region of periodic variability.
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the environment of the strongest galactic methanol Maser
arXiv: Astrophysics of Galaxies, 2015Co-Authors: A Sanna, S P Ellingsen, A Brunthaler, M J Reid, K M Menten, L Moscadelli, R Cesaroni, Carlos Carrascogonzalez, V KrishnanAbstract:The high-mass star-forming site G009.62+00.20E hosts the 6.7 GHz methanol Maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last ten years. We performed high-resolution astrometric measurements of the CH3OH, H2O, and OH Maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH3OH Maser cloudlets are distributed along two north-south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH3OH Maser transitions. We suggest that the periodic Maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest Masers. We also report about the discovery of an elliptical distribution of CH3OH Maser emission in the region of periodic variability.
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a search for gravitationally lensed water Masers in dusty quasars and star forming galaxies
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: J P Mckean, C Henkel, A Brunthaler, C M V Impellizzeri, A L Roy, P Castangia, F Samuel, O WucknitzAbstract:Luminous extra-galactic water Masers are known to be associated with active galactic nuclei and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the circumnuclear accretion disk i n nearby galaxies. To find water Maser systems at much higher redshifts, we have begun a survey of known gravitationally lensed quasars and star-forming galaxies. In this paper, we present a search for 22 GHz (rest frame) water Masers toward five dusty, gravitationally lens ed quasars and star-forming galaxies at redshifts between 2.3 and 2.9 with the Effelsberg radio telescope and the Expanded Very Large Array. Our observations do not find any new definite exam ples of high redshift water Maser galaxies, suggesting that large reservoirs of dust an d gas are not a sufficient condition for powerful water Maser emission. However, we do find the ten tative detection of a water Maser system in the active galaxy IRAS 10214+4724 at redshift 2.285. Our survey has now doubled the number of gravitationally lensed galaxies and quasars that have been searched for high redshift water Maser emission. We also present an updated analysis of the high redshift water Maser luminosity function that is based on the results presented here and from the only cosmologically distant (z > 1) water Maser galaxy found thus far, MG J0414+0534 at redshift 2.64. By comparing with the water Maser luminosity function locally and at moderate redshifts, we find that there must be some evolution in the luminosity function of water Maser galaxies at high redshifts. By assuming a moderate evolution [(1 + z) 4 ] in the water Maser luminosity function, we find that blind surveys for water Maser galaxies are only worthwhile with extremely high sensitivity like that of the planned Square Kilometre Array (Phase 2), which is scheduled to be completed by 2020. However, instruments like the EVLA and MeerKAT will be capable of detecting water Maser systems similar to the one found from MG J0414+0534 through dedicated pointed observations, providing suitable high-redshift targets can be selected.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
Astronomy and Astrophysics, 2011Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:Context. Both 22 GHz water and 6.7 GHz methanol Masers are usually interpreted as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments in which they occur. Aims. We attempt to derive accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission mapped earlier with Very Long Baseline Interferometry. Methods. We searched for 22 GHz water Masers in 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Results. Water Maser clusters are detected towards 27 sites leading to the identification of 15 new sources. The detection rate of water Maser emission associated with methanol sources is as high as 71%. In a large number of objects (18/21), the structure of water Maser is well aligned with that of the extended emission at 4.5 μm confirming the origin of water emission in outflows. The sources of methanol emission with ring-like morphologies, which likely trace a circumstellar disc/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. Conclusions. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario where 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appear to trace outflows. The two types of associations may be related to different evolutionary phases.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
arXiv: Astrophysics of Galaxies, 2010Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:22 GHz water and 6.7 GHz methanol Masers are usually thought as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments they occur in. The aim was to obtain accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission recently mapped with Very Long Baseline Interferometry. A sample of 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Water Maser clusters were detected towards 27 sites finding 15 new sources. The detection rate of water Maser emission associated with methanol sources was as high as 71%. In a large number of objects (18/21) the structure of water Maser is well aligned with that of the extended emission at 4.5 $\mu$m confirming the origin of water emission from outflows. The sources with methanol emission with ring-like morphologies, which likely trace a circumstellar disk/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario that 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appears to trace outflows. The two types of associations might be related to different evolutionary phases.
Doyoung Byun - One of the best experts on this subject based on the ideXlab platform.
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a multi epoch simultaneous water and methanol Maser survey toward intermediate mass young stellar objects
Astrophysical Journal Supplement Series, 2011Co-Authors: Jaehan Bae, Keetae Kim, Soyoung Youn, Wonju Kim, Doyoung Byun, Hyunwoo KangAbstract:We report a multi-epoch, simultaneous 22 GHz H2O and 44 GHz Class I CH3OH Maser line survey toward 180 intermediate-mass young stellar objects, including 14 Class 0 and 19 Class I objects, and 147 Herbig Ae/Be stars. We detected H2O and CH3OH Maser emission toward 16 (9%) and 10 (6%) sources with one new H2O and six new CH3OH Maser sources. The detection rates of both Masers rapidly decrease as the central (proto)stars evolve, which is contrary to the trends in high-mass star-forming regions. This suggests that the excitations of the two Masers are closely related to the evolutionary stage of the central (proto)stars and the circumstellar environments. H2O Maser velocities deviate on average 9 km s–1 from the ambient gas velocities whereas CH3OH Maser velocities match quite well with the ambient gas velocities. For both Maser emissions, large velocity differences ( 10 \mbox{\,km\,s$^{-1}$}$ SRC=http://ej.iop.org/images/0067-0049/196/2/21/apjs404366ieqn1.gif/> and 1 \mbox{\,km\,s$^{-1}$}$ SRC=http://ej.iop.org/images/0067-0049/196/2/21/apjs404366ieqn2.gif/>) are mostly confined to Class 0 objects. The formation and disappearance of H2O Masers is frequent and their integrated intensities change by up to two orders of magnitude. In contrast, CH3OH Maser lines usually show no significant change in intensity, shape, or velocity. This is consistent with the previous suggestion that H2O Maser emission originates from the base of an outflow while 44 GHz Class I CH3OH Maser emission arises from the interaction region of the outflow with the ambient gas. The isotropic Maser luminosities are well correlated with the bolometric luminosities of the central objects. The fitted relations are and .
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a multi epoch simultaneous water and methanol Maser survey toward intermediate mass young stellar objects
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Jaehan Bae, Keetae Kim, Soyoung Youn, Wonju Kim, Doyoung Byun, Hyunwoo KangAbstract:We report a multi-epoch, simultaneous 22 GHz H2O and 44 GHz class I CH3OH Maser line survey towards 180 intermediate-mass young stellar objects, including 14 Class 0, 19 Class I objects, and 147 Herbig Ae/Be stars. We detected H2O and CH3OH Maser emission towards 16 (9%) and 10 (6%) sources with one new H2O and six new CH3OH Maser sources. The detection rates of both Masers rapidly decrease as the central (proto)stars evolve, which is contrary to the trends in high-mass star-forming regions. This suggests that the excitations of the two Masers are closely related to the evolutionary stage of the central (proto)stars and the circumstellar environments. H2O Maser velocities deviate on average 9 km s^-1 from the ambient gas velocities whereas CH3OH Maser velocities match quite well with the ambient gas velocities. For both Maser emissions, large velocity differences (|v_{H2O} - v_{sys} | > 10 km s^-1 and |v_{CH3OH} - v_{sys}| > 1 km s^-1) are mostly confined to Class 0 objects. The formation and disappearance of H2O Masers is frequent and their integrated intensities change by up to two orders of magnitude. In contrast, CH3OH Maser lines usually show no significant change in intensity, shape, or velocity. This is consistent with the previous suggestion that H2O Maser emission originates from the base of an outflow while 44 GHz class I CH3OH Maser emission arises from the interaction region of the outflow with the ambient gas. The isotropic Maser luminosities are well correlated with the bolometric luminosities of the central objects. The fitted relations are L_{H2O} = 1.71 * 10^{-9} (L_{bol})^{0.97} and L_{CH3OH} = 1.71 * 10^{-10} (L_{bol})^{1.22}.
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simultaneous observations of sio and h 2 o Masers toward known stellar sio and h 2 o Maser sources i
Astrophysical Journal Supplement Series, 2010Co-Authors: Doyoung Byun, Jaeheon Kim, Sehyung ChoAbstract:We present the results of simultaneous observations of both SiO and H2O Masers toward 166 known SiO and H2O Maser sources using the Korean VLBI Network Yonsei 21 m radio telescope during 2009 June. Both SiO and H2O Maser emission were detected from 112 sources giving a detection rate of 67% at one epoch observation. SiO-only Maser emission was detected from 42 sources, while H2O-only Maser emission was detected from four sources. Most of the SiO Masers appear around the stellar velocity, while H2O Masers show different characteristics compared with SiO Masers. There are more than 20 sources that show a one-way peak or double peaks with respect to the stellar velocity and SiO Maser peak velocity. The H2O Maser peak and integrated intensity ratios with respect to those of SiO (v = 1) show increasingly larger values from Mira variables, to OH/IR stars, to semi-regular variables. In addition, the IRAS two-color diagram of SiO and H2O Maser observational results is discussed.
A Bartkiewicz - One of the best experts on this subject based on the ideXlab platform.
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discovery of periodic and alternating flares of the methanol and water Masers in g107 298 5 639
Monthly Notices of the Royal Astronomical Society: Letters, 2016Co-Authors: M Szymczak, A Bartkiewicz, M Olech, P Wolak, M P GawronskiAbstract:Methanol and water vapour Masers are signposts of early stages of high-mass star formation but it is generally thought that due to different excitation processes they probe distinct parts of stellar environments. Here we present observations of the intermediate-mass young stellar object G107.298+5.639, revealing for the first time that 34.4 d flares of the 6.7 GHz methanol Maser emission alternate with flares of individual features of the 22 GHz water Maser. High angular resolution data reveal that a few components of both Maser species showing periodic behaviour coincide in position and velocity and all the periodic water Maser components appear in the methanol Maser region of size of 360 au. The Maser flares could be caused by variations in the infrared radiation field induced by cyclic accretion instabilities in a circumstellar or protobinary disc. The observations do not support either the stellar pulsations or the seed photon flux variations as the underlying mechanisms of the periodicity in the source.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
Astronomy and Astrophysics, 2011Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:Context. Both 22 GHz water and 6.7 GHz methanol Masers are usually interpreted as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments in which they occur. Aims. We attempt to derive accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission mapped earlier with Very Long Baseline Interferometry. Methods. We searched for 22 GHz water Masers in 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Results. Water Maser clusters are detected towards 27 sites leading to the identification of 15 new sources. The detection rate of water Maser emission associated with methanol sources is as high as 71%. In a large number of objects (18/21), the structure of water Maser is well aligned with that of the extended emission at 4.5 μm confirming the origin of water emission in outflows. The sources of methanol emission with ring-like morphologies, which likely trace a circumstellar disc/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. Conclusions. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario where 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appear to trace outflows. The two types of associations may be related to different evolutionary phases.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
arXiv: Astrophysics of Galaxies, 2010Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:22 GHz water and 6.7 GHz methanol Masers are usually thought as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments they occur in. The aim was to obtain accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission recently mapped with Very Long Baseline Interferometry. A sample of 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Water Maser clusters were detected towards 27 sites finding 15 new sources. The detection rate of water Maser emission associated with methanol sources was as high as 71%. In a large number of objects (18/21) the structure of water Maser is well aligned with that of the extended emission at 4.5 $\mu$m confirming the origin of water emission from outflows. The sources with methanol emission with ring-like morphologies, which likely trace a circumstellar disk/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario that 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appears to trace outflows. The two types of associations might be related to different evolutionary phases.
M Szymczak - One of the best experts on this subject based on the ideXlab platform.
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discovery of periodic and alternating flares of the methanol and water Masers in g107 298 5 639
Monthly Notices of the Royal Astronomical Society: Letters, 2016Co-Authors: M Szymczak, A Bartkiewicz, M Olech, P Wolak, M P GawronskiAbstract:Methanol and water vapour Masers are signposts of early stages of high-mass star formation but it is generally thought that due to different excitation processes they probe distinct parts of stellar environments. Here we present observations of the intermediate-mass young stellar object G107.298+5.639, revealing for the first time that 34.4 d flares of the 6.7 GHz methanol Maser emission alternate with flares of individual features of the 22 GHz water Maser. High angular resolution data reveal that a few components of both Maser species showing periodic behaviour coincide in position and velocity and all the periodic water Maser components appear in the methanol Maser region of size of 360 au. The Maser flares could be caused by variations in the infrared radiation field induced by cyclic accretion instabilities in a circumstellar or protobinary disc. The observations do not support either the stellar pulsations or the seed photon flux variations as the underlying mechanisms of the periodicity in the source.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
Astronomy and Astrophysics, 2011Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:Context. Both 22 GHz water and 6.7 GHz methanol Masers are usually interpreted as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments in which they occur. Aims. We attempt to derive accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission mapped earlier with Very Long Baseline Interferometry. Methods. We searched for 22 GHz water Masers in 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Results. Water Maser clusters are detected towards 27 sites leading to the identification of 15 new sources. The detection rate of water Maser emission associated with methanol sources is as high as 71%. In a large number of objects (18/21), the structure of water Maser is well aligned with that of the extended emission at 4.5 μm confirming the origin of water emission in outflows. The sources of methanol emission with ring-like morphologies, which likely trace a circumstellar disc/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. Conclusions. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario where 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appear to trace outflows. The two types of associations may be related to different evolutionary phases.
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vla observations of water Masers towards 6 7 ghz methanol Maser sources
arXiv: Astrophysics of Galaxies, 2010Co-Authors: A Bartkiewicz, A Brunthaler, M Szymczak, Y M Pihlstrom, H J Van Langevelde, M J ReidAbstract:22 GHz water and 6.7 GHz methanol Masers are usually thought as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments they occur in. The aim was to obtain accurate positions and morphologies of the water Maser emission and relate them to the methanol Maser emission recently mapped with Very Long Baseline Interferometry. A sample of 31 methanol Maser sources was searched for 22 GHz water Masers using the VLA and observed in the 6.7 GHz methanol Maser line with the 32 m Torun dish simultaneously. Water Maser clusters were detected towards 27 sites finding 15 new sources. The detection rate of water Maser emission associated with methanol sources was as high as 71%. In a large number of objects (18/21) the structure of water Maser is well aligned with that of the extended emission at 4.5 $\mu$m confirming the origin of water emission from outflows. The sources with methanol emission with ring-like morphologies, which likely trace a circumstellar disk/torus, either do not show associated water Masers or the distribution of water Maser spots is orthogonal to the major axis of the ring. The two Maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol Maser emission in a minority of sources is consistent with a scenario that 6.7 GHz methanol Masers trace a disc/torus around a protostar while the associated 22 GHz water Masers arise in outflows. The majority of sources in which methanol Maser emission is associated with the water Maser appears to trace outflows. The two types of associations might be related to different evolutionary phases.
