Nucleosynthesis in AGB stars traced by oxygen isotopic ratios: I. Determining the stellar initial mass by means of the super(17) O/ super(18) O ratio

Aims. We seek to investigate the super(17) O/ super(18) O ratio for a sample of AGB stars containing M-, S-, and C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period. Methods. Circumstellar super(13) C super(1...

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Published in:Astronomy and astrophysics (Berlin) 2017-04, Vol.600
Main Authors: De Nutte, R, Decin, L, Olofsson, H, Lombaert, R, de Koter, A, Karakas, A, Milam, S, Ramstedt, S, Stancliffe, R J, Homan, W, Van de Sande, M
Format: Article
Language:English
Subjects:
Astronomical models
Astronomy
Asymptotic giant branch stars
Constants
Mathematical models
Pulsation
Stars
Stellar evolution
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Summary:Aims. We seek to investigate the super(17) O/ super(18) O ratio for a sample of AGB stars containing M-, S-, and C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period. Methods. Circumstellar super(13) C super(16) O, super(12) C super(17) O, and super(12) C super(18) O line observations were obtained for a sample of nine stars with various single-dish long-wavelength facilities. Line intensity ratios are shown to relate directly to the surface super(17) O/ super(18) O abundance ratio. Results. Stellar evolution models predict the super(17) O/ super(18) O ratio to be a sensitive function of initial mass and to remain constant throughout the entire TP-AGB phase for stars initially less massive than 5M sub([middot in circle]). This makes the measured ratio a probe of the initial stellar mass. Conclusions. Observed super(17) O/ super(18) O ratios are found to be well in the range predicted by stellar evolution models that do not consider convective overshooting. From this, accurate initial mass estimates are calculated for seven sources. For the remaining two sources, there are two mass solutions, although there is a larger probability that the low-mass solution is correct. Finally, we present hints at a possible separation between M/S- and C-type stars when comparing the super(17) O/ super(18) O ratio to the stellar pulsation period.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201629195