A Search for Water Maser Emission from OH/IR Stars

Engels, D.; Schmid-Burgk, J.; Walmsley, C. M.

doi:10.1007/978-94-009-3813-7_13

Cited by 48 publications

(92 citation statements)

References 3 publications

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“…Crocker & Hagen (1983), indicating a velocity of about 3 km s −1 . Engels et al (1988) found a secondary feature in the line profile, suggesting that the H 2 O maser in this source shows some time variability. Both, the velocity structure as probed by the SiO 86 GHz maser, the 22 GHz H 2 O maser and the CO rotational lines and the mass-loss rate are in agreement with the properties of our B-type models (see also Sect.…”

Section: Narrow Profilesmentioning

confidence: 78%

Mass-loss from dusty, low outflow-velocity AGB stars

Winters

Bertre

Jeong

et al. 2003

A&A

112

164

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Abstract. We present the first results of a CO(2-1), (1-0), and 86 GHz SiO maser survey of AGB stars, selected by their weak near-infrared excess. Among the 65 sources of the present sample we find 10 objects with low CO outflow velocities, v exp < ∼ 5 km s −1 . Typically, these sources show (much) wider SiO maser features. Additionally, we get 5 sources with composite CO line profiles, i.e. a narrow feature is superimposed on a broader one, where both components are centered at the same stellar velocity. The gas mass-loss rates, outflow velocities and velocity structures suggested by these line profiles are compared with the results of hydrodynamical model calculations for dust forming molecular winds of pulsating AGB stars. The observations presented here give support to our recent low outflow-velocity models, in which only small amounts of dust are formed. Therefore, the wind generation in these models is dominated by stellar pulsation. We interpret the composite line profiles in terms of successive winds with different characteristics. Our hydrodynamical models, which show that the wind properties may be extremely sensitive to the stellar parameters, support such a scenario.

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Section: Narrow Profilesmentioning

confidence: 78%

Mass-loss from dusty, low outflow-velocity AGB stars

Winters

Bertre

Jeong

et al. 2003

A&A

112

164

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“…The maps hint at possible clumpiness in the gaseous component of the CSE. Estimates for the distance to this source vary from 1.8 kpc to 7 kpc, corresponding to a luminosity range from 6 × 10 3 L to 2.6 × 10 5 L (Herman & Habing 1985;Engels et al 1986;Bowers & Johnston 1990;Heske et al 1990;van Langevelde et al 1990;Kemper et al 2002). We follow Suh & Kim (2002), who take the pulsational phase into account while modeling the spectral energy distribution (SED).…”

Section: Target Selection and Data Reductionmentioning

confidence: 99%

H₂O vapor excitation in dusty AGB envelopes

Lombaert

Decin

Koter

et al. 2013

A&A

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Context. AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several molecules, including H 2 O. Aims. The dust and gas content of the envelope surrounding the high mass-loss rate OH/IR star OH 127.8+0.0, as traced by Herschel observations, is studied, with a focus on the H 2 O content and the dust-to-gas ratio. We report detecting a large number of H 2 O vapor emission lines up to J = 9 in the Herschel data, for which we present the measured line strengths. Methods. The treatments of both gas and dust species are combined using two numerical radiative transfer codes. The method is illustrated for both low and high mass-loss-rate sources. Specifically, we discuss different ways of assessing the dust-to-gas ratio: 1) from the dust thermal emission spectrum and the CO molecular gas line strengths; 2) from the momentum transfer from dust to gas and the measured gas terminal velocity; and 3) from the determination of the required amount of dust to reproduce H 2 O lines for a given H 2 O vapor abundance. These three diagnostics probe different zones of the outflow, for the first time allowing an investigation of a possible radial dependence of the dust-to-gas ratio. Results. We modeled the infrared continuum and the CO and H 2 O emission lines in OH 127.8+0.0 simultaneously. We find a dustmass-loss rate of (0.5 ± 0.1) × 10 −6 M yr −1 and an H 2 O ice fraction of 16% ± 2% with a crystalline-to-amorphous ratio of 0.8 ± 0.2. The gas temperature structure is modeled with a power law, leading to a constant gas-mass-loss rate between 2 × 10 −5 M yr −1 and 1 × 10 −4 M yr −1 , depending on the temperature profile. In addition, a change in mass-loss rate is needed to explain the J = 1−0 and J = 2−1 CO lines formed in the outer wind, where the older mass-loss rate is estimated to be 1 × 10 −7 M yr −1 . The dust-to-gas ratio found with method 1) is 0.01, accurate to within a factor of three; method 2) yields a lower limit of 0.0005; and method 3) results in an upper limit of 0.005. The H 2 O ice fraction leads to a minimum required H 2 O vapor abundance with respect to H 2 of (1.7 ± 0.2) × 10 −4 . Finally, we report detecting 1612 MHz OH maser pumping channels in the far-infrared at 79.1, 98.7, and 162.9 μm. Conclusions. Abundance predictions for a stellar atmosphere in local thermodynamic equilibrium yield a twice higher H 2 O vapor abundance (∼3 × 10 −4 ), suggesting a 50% freeze-out. This is considerably higher than current freeze-out predictions. Regarding the dust-to-gas ratio, methods 2) and 3) probe a deeper part of the envelope, while method 1) is sensitive to the outermost regions. The latter ...

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“…The snapshot revealed that the 22-GHz masers are weaker (in photon luminosity, peak and frequency-integrated intensity) than the SiO masers at most stellar phases, but that the water masers become relatively more powerful as stars become more massive, and have greater mass-loss rates -that is as stellar properties move from the Miras to the OH/IR stars (Engels et al 1986). More information about the effect of the circumstellar velocity field on the masers can be gleaned from the velocity extent and red/blue dominance in the spectra.…”

Section: Introductionmentioning

confidence: 99%

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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A Search for Water Maser Emission from OH/IR Stars

Cited by 48 publications

References 3 publications

Mass-loss from dusty, low outflow-velocity AGB stars

Mass-loss from dusty, low outflow-velocity AGB stars

H₂O vapor excitation in dusty AGB envelopes

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

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A Search for Water Maser Emission from OH/IR Stars

Cited by 48 publications

References 3 publications

Mass-loss from dusty, low outflow-velocity AGB stars

Mass-loss from dusty, low outflow-velocity AGB stars

H2O vapor excitation in dusty AGB envelopes

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

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H₂O vapor excitation in dusty AGB envelopes