Simulation of pumping mechanism of H<sub>2</sub>O-masers in circumstellar envelopes of late-type stars

Nesterenok, A. V.

doi:10.1088/1742-6596/461/1/012009

Cited by 5 publications

(3 citation statements)

References 10 publications

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“…The gain is substantially lower when the stellar radiation is taken into account; the cloud averaged gain γ at the parameters in question is about 0.8 × 10 −13 cm −1 and 1.5×10 −13 cm −1 for the models with and without stellar radiation, respectively (with a full set of ro-vibrational levels). Analogous results were found for the 22.2-GHz circumstellar maser by Nesterenok (2013b). Fig.…”

Section: Gain Of the 658-ghz Maser Linesupporting

confidence: 85%

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

Nesterenok

2015

Monthly Notices of the Royal Astronomical Society

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The model is presented of H 2 O maser in the 1 10 − 1 01 line within the first excited vibrational state of the molecule around oxygen-rich asymptotic giant branch stars. It is suggested that the maser cloud is located in the inner layers of the circumstellar envelope where intense dust formation takes place. The calculations took into account rotational levels belonging to the five lowest vibrational states of the H 2 O molecule. The model predicts the gain values of the 658-GHz maser about 10 −14 − 10 −13 cm −1 at H 2 molecule concentrations 10 9 − 10 11 cm −3 and at high ortho-H 2 O concentrations 10 5 cm −3 . The gas temperatures 1000 -1500 K are considered to be a necessary condition for the effective maser operation. Results are presented for other maser transitions of the excited vibrational states of the molecule.

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Section: Gain Of the 658-ghz Maser Linesupporting

confidence: 85%

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

Nesterenok

2015

Monthly Notices of the Royal Astronomical Society

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“…Recent ALI modelling of the 22-GHz maser with up-to-date molecular data (Nesterenok 2013) reinforces the usual view that a substantial radiation field in the far-and mid-infra-red is harmful to the 22-GHz inversion.…”

Section: Water Maser Theory and Modellingmentioning

confidence: 63%

The physics of water masers observable with ALMA and SOFIA: model predictions for evolved stars

Gray

Baudry

Richards

et al. 2015

Mon. Not. R. Astron. Soc.

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We present the results of models that were designed to study all possible water maser transitions in the frequency range 0-1.91 THz, with particular emphasis on maser transitions that may be generated in evolved-star envelopes and observed with the ALMA and SOFIA telescopes. We used tens of thousands of radiative transfer models of both spin species of H 2 O, spanning a considerable parameter space in number density, kinetic temperature and dust temperature. Results, in the form of maser optical depths, have been summarized in a master table, Table 6. Maser transitions identified in these models were grouped according to loci of inverted regions in the density/kinetic temperature plane, a property clearly related to the dominant mode of pumping. A more detailed study of the effect of dust temperature on maser optical depth enabled us to divide the maser transitions into three groups: those with both collisional and radiative pumping schemes (22,96,209,321,325,395,941 and 1486 GHz), a much larger set that are predominantly radiatively pumped, and another large group with a predominantly collisional pump. The effect of accelerative and decelerative velocity shifts of up to 5 km s −1 was found to be generally modest, with the primary effect of reducing computed maser optical depths. More subtle asymmetric effects, dependent on line overlap, include maximum gains offset from zero shift by >1 km s −1 , but these effects were predominantly found under conditions of weak amplification. These models will allow astronomers to use multi-transition water maser observations to constrain physical conditions down to the size of individual masing clouds (size of a few astronomical units).

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“…Theoretical models generally indicate that the gas density and kinetic temperature favouring both maser transitions do not overlap (Cragg et al 2002;Gray et al 2016). However, modelling of the 22 GHz maser excitation with up-to-date molecular data (Nesterenok 2013) supports the view that the inversion is most efficient when the dust temperature is much lower than the gas temperature and an increase of the infrared emission reduces the maser gain (Yates et al 1997).…”

Section: Anti-correlated Variability Of Ch 3 Oh and H 2 O Masersmentioning

confidence: 94%

Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

Олеч

Szymczak

Wolak

et al. 2020

A&A

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Context. Periodic flares of maser emission are thought to be induced either by variations of the seed photon flux in young binary systems or the pump rate regulated by stellar and accretion luminosities. Aims. We seek to study the variability of four maser transitions of three different species in G107.298+5.639 to constrain the dominant mechanism of periodic flares. Methods. Light curves of the 6.7 GHz methanol and 22.2 GHz water vapour maser were obtained with the Torun 32 m radio telescope over 39 and 34 cycles, respectively. The target was also monitored at the 1.6 GHz hydroxyl transitions with the Nançay radio telescope over 13 cycles. All these maser lines were imaged using VLBI arrays.Results. The study confirms alternating flares of the methanol and water masers with a period of 34.4 d and reveals the synchronised behaviour of the methanol and hydroxyl masers in this source. The observed spatial distribution of the methanol maser cloudlets and the measured time delays of the flares of individual features imply a ring-like structure of radius 240 au and thickness 30 au. Internal proper motions indicate that the velocity of methanol cloudlets is dominated by a disc-wind component of about 5 km s −1 . The methanol emission detected during only one VLBI observation is located in a region about 550 au from a central star, which also exhibits OH maser flares. The erratic appearance of methanol features can be related to a powering object of relatively low luminosity which, during some variability cycles, can excite molecules only in the nearest part of the disc. A careful analysis of the maser and infrared light curves reveal a strong correlation between the 6.7 GHz line and the infrared flux densities supporting a radiative pumping of the maser. Conclusions. The synchronised behaviour of the hydroxyl 1665/1667 MHz and 6.7 GHz methanol transitions indicates a common pumping mechanism for the periodic flares of G107.298+5.639.

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Simulation of pumping mechanism of H₂O-masers in circumstellar envelopes of late-type stars

Cited by 5 publications

References 10 publications

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

The physics of water masers observable with ALMA and SOFIA: model predictions for evolved stars

Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

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Simulation of pumping mechanism of H2O-masers in circumstellar envelopes of late-type stars

Cited by 5 publications

References 10 publications

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

Model of the vibrationally excited H2O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars

The physics of water masers observable with ALMA and SOFIA: model predictions for evolved stars

Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

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Simulation of pumping mechanism of H₂O-masers in circumstellar envelopes of late-type stars