Herschel observations of extreme OH/IR stars: The isotopic ratios of oxygen as a sign-post for the stellar mass
Journal article, 2015

© ESO 2015. Aims. The late stages of stellar evolution are mainly governed by the mass of the stars. Low- and intermediate-mass stars lose copious amounts of mass during the asymptotic giant branch (AGB) which obscure the central star making it difficult to study the stellar spectra and determine the stellar mass. In this study, we present observational data that can be used to determine lower limits to the stellar mass. Methods. Spectra of nine heavily reddened AGB stars taken by the Herschel Space Observatory display numerous molecular emission lines. The strongest emission lines are due to H 2 O. We search for the presence of isotopologues of H 2 O in these objects. Results. We detected the 16O and 17O isotopologues of water in these stars, but lines due to H 2 18O are absent. The lack of 18O is predicted by a scenario where the star has undergone hot-bottom burning which preferentially destroys 18O relative to 16O and 17O. From stellar evolution calculations, this process is thought to occur when the stellar mass is above 5 M ⊙ for solar metallicity. Hence, observations of different isotopologues of H 2 O can be used to help determine the lower limit to the initial stellar mass. Conclusions. From our observations, we deduce that these extreme OH/IR stars are intermediate-mass stars with masses of ≥5 M ⊙ . Their high mass-loss rates of ∼10-4M ⊙ yr-1 may affect the enrichment of the interstellar medium and the overall chemical evolution of our Galaxy.

Circumstellar matter

Submillimeter: stars

Stars: mass-loss

Stars: evolution

Stars: AGB and post-AGB

Author

Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

M. J. Barlow

University College London (UCL)

Jadl Blommaert

Vrije Universiteit Brussel (VUB)

Vlaamse Instelling voor Technologisch Onderzoek n.v. (VITO)

L. Decin

KU Leuven

F. Kerschbaum

University of Vienna

M. Matsuura

University College London (UCL)

Cardiff University

Hans Olofsson

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

P. Owen

University College London (UCL)

P. Royer

KU Leuven

B. Swinyard

Rutherford Appleton Laboratory

University College London (UCL)

D. Teyssier

European Space Astronomy Centre (ESAC)

Lbfm Waters

Netherlands Institute for Space Research (SRON)

University of Amsterdam

J. A. Yates

University College London (UCL)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 578 A115

Subject Categories

Fusion, Plasma and Space Physics

DOI

10.1051/0004-6361/201526270

More information

Latest update

9/6/2018 1