English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Aims: By performing a detailed radiative transfer analysis, we determinefractional abundances of circumstellar H2O in the envelopes around six M-typeasymptotic giant branch stars. The models are also used to predict H2O spectralline emission for the upcoming Herschel/HIFI mission.  Methods: We use Infrared space observatory long wavelength spectrometerspectra to constrain the circumstellar fractional abundance distribution ofortho-H2O, using a non-local thermal equilibrium, and non-local, radiativetransfer code based on the accelerated lambda iteration formalism. Themass-loss rates and kinetic temperature structures for the sample stars aredetermined through radiative transfer modelling of CO line emission based onthe Monte-Carlo method. The density and temperature profiles of thecircumstellar dust grains are determined through spectral energy distributionmodelling using the publicly available code Dusty.  Results: The determined ortho-H2O abundances lie between 1e-4 and 1.5e-3relative to H2, with the exception of WX Psc, which has a much lower estimatedortho-H2O abundance of only 2e-6, possibly indicating H_2O adsorption onto dustgrains or recent mass-loss-rate modulations. The estimated abundances areuncertain by, at best, a factor of a few.  Conclusions: The high water abundance found for the majority of the sourcessuggests that either the `normal' chemical processes are very effective inproducing H2O, or else non-local thermal equilibrium atmospheric chemistry,grain surface reactions, or a release of H_2O (e.g. from icy bodies like Kuiperbelt objects) play a role. We provide predictions for ortho-H2O lines in thespectral window of Herschel/HIFI.

Circumstellar water vapour in M-type AGB stars: Radiative transfer models, abundances and predictions for HIFI