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Water isotopologues in the circumstellar envelopes of M-type AGB stars

T. Danilovich ; Robin Lombaert (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; L. Decin ; A. Karakas ; Matthias Maercker (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; Hans Olofsson (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium)
Astronomy and Astrophysics (0004-6361). Vol. 602 (2017), p. Article number A14.
[Artikel, refereegranskad vetenskaplig]

Aims. In this study we intend to examine rotational emission lines of two isotopologues of water: H2 17O and H2 18O. By determining the abundances of these molecules, we aim to use the derived isotopologue - and hence oxygen isotope - ratios to put constraints on the masses of a sample of M-type AGB stars that have not been classified as OH/IR stars. Methods. We have used detailed radiative transfer analysis based on the accelerated lambda iteration method to model the circumstellar molecular line emission of H2 17O and H2 18O for IK Tau, R Dor, W Hya, and R Cas. The emission lines used to constrain our models came from Herschel/HIFI and Herschel/PACS observations and are all optically thick, meaning that full radiative transfer analysis is the only viable method of estimating molecular abundance ratios. Results. We find generally low values of the 17O/18O ratio for our sample, ranging from 0.15 to 0.69. This correlates with relatively low initial masses, in the range ~ 1.0 to 1.5 M? for each source, based on stellar evolutionary models. We also find ortho-to-para ratios close to 3, which are expected from warm formation predictions. Conclusions. The 17O/18O ratios found for this sample are at the lower end of the range predicted by stellar evolutionary models, indicating that the sample chosen had relatively low initial masses.

Nyckelord: Circumstellar matter; Stars: AGB and post-AGB; Stars: fundamental parameters

Denna post skapades 2017-10-04. Senast ändrad 2017-10-10.
CPL Pubid: 252301


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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium (2010-2017)


Astronomi, astrofysik och kosmologi

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