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.
Stars: mass-loss
Stars: evolution
Submillimeter: stars
Stars: AGB and post-AGB
Circumstellar matter
Author
Kay Justtanont
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
M. J. Barlow
University College London (UCL)
Jadl Blommaert
Flemish Institute for Technological Research
Vrije Universiteit Brussel (VUB)
L. Decin
KU Leuven
F. Kerschbaum
University of Vienna
M. Matsuura
Cardiff University
University College London (UCL)
Hans Olofsson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
P. Owen
University College London (UCL)
P. Royer
KU Leuven
B. Swinyard
University College London (UCL)
STFC Rutherford Appleton Laboratory
D. Teyssier
European Space Astronomy Centre (ESAC)
Lbfm Waters
University of Amsterdam
Netherlands Institute for Space Research (SRON)
J. A. Yates
University College London (UCL)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 578 A115Subject Categories
Fusion, Plasma and Space Physics
DOI
10.1051/0004-6361/201526270