Collisional excitation of water in warm astrophysical media

Fauré, Alexandre; Josselin, E.

doi:10.1051/0004-6361:200810717

Cited by 94 publications

(125 citation statements)

References 35 publications

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“…This model does not intend to fit any particular object. A large non-LTE H 2 O ro-vibrational model calculation was included to consistently calculate the Spitzer as well as the Herschel H 2 O emission lines by applying escape probability theory (Faure et al 2004(Faure et al , 2007Faure & Josselin 2008). At ∼3 AU, the gas densities are high enough to excite the 63.32 μm o-H 2 O line and the dust temperature close to the mid-plane is low enough for H 2 O to freeze onto grains.…”

Section: Resultsmentioning

confidence: 99%

Detection of warm water vapour in Taurus protoplanetary discs byHerschel

Riviére-Marichalar

Ménard

Thi

et al. 2012

A&A

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Line spectra of 68 Taurus T Tauri stars were obtained with the Herschel-PACS (Photodetector Array Camera and Spectrometer) instrument as part of the GASPS (GAS evolution in Protoplanetary Systems) survey of protoplanetary discs. A careful examination of the linescans centred on the [OI] 63.18 μm fine-structure line unveiled a line at 63.32 μm in some of these spectra. We identify this line with the 8 18 → 7 07 transition of ortho-water. It is detected confidently (i.e., >3σ) in eight sources, i.e., ∼24% of the sub-sample with gas-rich discs. Several statistical tests were used to search for correlations with other disc and stellar parameters such as line fluxes of [O i] 6300 Å and 63.18 μm; X-ray luminosity and continuum levels at 63 μm and 850 μm. Correlations are found between the water line fluxes and the [O i] 63.18 μm line luminosity, the dust continuum, and possibly with the stellar X-ray luminosity. This is the first time that this line of warm water vapour has been detected in protoplanetary discs. We discuss its origins, in particular whether it comes from the inner disc and/or disc surface or from shocks in outflows and jets. Our analysis favours a disc origin, with the observed water vapour line produced within 2-3 AU from the central stars, where the gas temperature is of the order of 500-600 K.

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Section: Resultsmentioning

confidence: 99%

Detection of warm water vapour in Taurus protoplanetary discs byHerschel

Riviére-Marichalar

Ménard

Thi

et al. 2012

A&A

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“…The rotational rate coefficients used here are based on the results of Green et al (1993), as are those of Neufeld & Kaufman (1993). Faure & Josselin (2008) recently calculated new rotational rates and compared them to those of Neufeld & Kaufman (1993), finding higher cooling rates for temperatures < ∼ 1500 K and lower cooling rates for temperatures > ∼ 1500 K. They also found that the rotational rate coefficients can be uncertain by factors of a few up to an order of magnitude, which is reflected in the uncertainties on the cooling rates.…”

Section: Gas Kinetic Temperature: Inmentioning

confidence: 99%

Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles

Beck

Decin

Koter

et al. 2010

A&A

236

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Context. The evolution of intermediate and low-mass stars on the asymptotic giant branch is dominated by their strong dust-driven winds. More massive stars evolve into red supergiants with a similar envelope structure and strong wind. These stellar winds are a prime source for the chemical enrichment of the interstellar medium. Aims. We aim to (1) set up simple and general analytical expressions to estimate mass-loss rates of evolved stars, and (2) from those calculate estimates for the mass-loss rates of the asymptotic giant branch, red supergiant, and yellow hypergiant stars in our galactic sample. Methods. The rotationally excited lines of carbon monoxide (CO) are a classic and very robust diagnostic in the study of circumstellar envelopes. When sampling different layers of the circumstellar envelope, observations of these molecular lines lead to detailed profiles of kinetic temperature, expansion velocity, and density. A state-of-the-art, nonlocal thermal equilibrium, and co-moving frame radiative transfer code that predicts CO line intensities in the circumstellar envelopes of late-type stars is used in deriving relations between stellar and molecular-line parameters, on the one hand, and mass-loss rate, on the other. These expressions are applied to our extensive CO data set to estimate the mass-loss rates of 47 sample stars. Results. We present analytical expressions for estimating the mass-loss rates of evolved stellar objects for 8 rotational transitions of the CO molecule and thencompare our results to those of previous studies. Our expressions account for line saturation and resolving of the envelope, thereby allowing accurate determination of very high mass-loss rates. We argue that, for estimates based on a single rotational line, the CO(2-1) transition provides the most reliable mass-loss rate. The mass-loss rates calculated for the asympotic giant branch stars range from 4 × 10 −8 M yr −1 up to 8 × 10 −5 M yr −1 . For red supergiants they reach values between 2 × 10 −7 M yr −1 and 3 × 10 −4 M yr −1 . The estimates for the set of CO transitions allow time variability to be identified in the mass-loss rate. Possible mass-loss-rate variability is traced for 7 of the sample stars. We find a clear relation between the pulsation periods of the asympotic giant branch stars and their derived mass-loss rates, with a levelling off at ∼3 × 10 −5 M yr −1 for periods exceeding 850 days. Conclusions.

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“…Within these files, one for each spin species of H2O, additional comment lines credit the energy level data to Tennyson et al (2001) and the Einstein A-values to Barber et al (2006). Collisional data is divided between two collisional partners: H2 molecules and free electrons (Faure & Josselin 2008).…”

Section: Molecular Datamentioning

confidence: 99%

“…Collision data for both spin species of H2O and molecular hydrogen do not specify the spin species of H2 used; in fact they are an average of ortho-and para-H2 contributions, assuming the thermal abundance ratio of 3 o-H2 to 1 p-H2. This is considered adequate for temperatures above 200 K (the lowest tabulated by Faure & Josselin 2008). The effect of changing sets of rate coefficients in numerical calculations has been considered by Daniel & Cernicharo (2013), who concluded that, in models of H2O masers, the likely uncertainty introduced into maser optical depths is a factor of 2 in the worst cases.…”

Section: Molecular Datamentioning

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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Collisional excitation of water in warm astrophysical media

Cited by 94 publications

References 35 publications

Detection of warm water vapour in Taurus protoplanetary discs byHerschel

Detection of warm water vapour in Taurus protoplanetary discs byHerschel

Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles

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

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