Mon. Not. R. Astron. Soc., 473, 241-260 (2018/January-1)
On the production of He, C, and N by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances.
HENRY R.B.C., STEPHENSON B.G., MILLER BERTOLAMI M.M., KWITTER K.B. and BALICK B.
Abstract (from CDS):
The primary goal of this paper is to make a direct comparison between the measured and model-predicted abundances of He, C, and N in a sample of 35 well-observed Galactic planetary nebulae (PNe). All observations, data reductions, and abundance determinations were performed in house to ensure maximum homogeneity. Progenitor star masses (M <= 4 M☉) were inferred using two published sets of post-asymptotic giant branch model tracks and L and Teff values. We conclude the following: (1) the mean values of N/O across the progenitor mass range exceeds the solar value, indicating significant N enrichment in the majority of our objects; (2) the onset of hot bottom burning appears to begin around 2 M☉, i.e. lower than ∼5 M☉ implied by theory; (3) most of our objects show a clear He enrichment, as expected from dredge-up episodes; (4) the average sample C/O value is 1.23, consistent with the effects of third dredge up; and (5) model grids used to compare to observations successfully span the distribution over metallicity space of all C/O and many He/H data points but mostly fail to do so in the case of N/O. The evident enrichment of N in PN and the general discrepancy between the observed and model-predicted N/O abundance ratios signal the need for extra mixing as an effect of rotation and/or thermohaline mixing in the models. The unexpectedly high N enrichment that is implied here for low-mass stars, if confirmed, will likely impact our conclusions about the source of N in the Universe.
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
stars: AGB and post-AGB - stars: evolution - ISM: abundances - planetary nebulae: general - galaxies: abundances - galaxies: ISM - galaxies: ISM
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