Herschel observations of extreme OH/IR stars: The isotopic ratios of oxygen as a sign-post for the stellar mass
Artikel i vetenskaplig tidskrift, 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.

Submillimeter: stars

Stars: evolution

Stars: AGB and post-AGB

Stars: mass-loss

Circumstellar matter


Kay Justtanont

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. J. Barlow

University College London (UCL)

Jadl Blommaert

Vrije Universiteit Brussel


L. Decin

KU Leuven

F. Kerschbaum

Universität Wien

M. Matsuura

Cardiff University

University College London (UCL)

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

P. Owen

University College London (UCL)

P. Royer

KU Leuven

B. Swinyard

University College London (UCL)

Rutherford Appleton Laboratory

D. Teyssier

European Space Astronomy Centre

Lbfm Waters

SRON Netherlands Institute for Space Research

Universiteit Van Amsterdam

J. A. Yates

University College London (UCL)

Astronomy and Astrophysics

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

Vol. 578 A115


Fusion, plasma och rymdfysik