The planetary nebulae and HII regions in NGC6822 revisited. Clues to AGB nucleosynthesis
Por:
García-Rojas J., Peña M., Flores-Durán S., Hernández-Martínez L.
Publicada:
1 feb 2016
Resumen:
Aims. The chemical behaviour of an ample sample of planetary nebulae
PNe) in NGC6822 is analysed.
Methods. Spectrophotometric data of 11 PNe and two H i i regions were
obtained with the OSIRIS spectrograph attached to the Gran Telescopio
Canarias. Data for other 13 PNe and three H i i regions were retrieved
from the literature. Physical conditions and chemical abundances of O,
N, Ne, Ar, and S were derived in a consistent way for 19 PNe and 4 H i i
regions.
Results. Abundances in the PNe sample are widely distributed showing 12
+ log O/H) from 7.4 to 8.2 and 12 + log Ar/H) from 4.97 to 5.80. Two
groups of PNe can be differentiated: one old with low metallicity 12 +
log O/H) < 8.0 and 12 + log Ar/H) < 5.7) and another younger one with
metallicities similar to the values for H i i regions. The old objects
are distributed in a larger volume than the young ones. An important
fraction of PNe over 30%) was found to be highly N-rich Peimbert Type I
PNe). Such PNe occur at any metallicity. In addition, about 60% of the
sample presents high ionization He (++)/He >= 0.1), possessing a central
star with effective temperature higher than 100 000 K. Possible biases
in the sample are discussed. From comparison with stellar evolution
models by Karakas 2010) and Fishlock et al. 2014) of the observed N/O
abundance ratios, our PNe should have had initial masses that are lower
than 4 M-circle dot, although if the comparison is made with Ne vs. O
abundances, the initial masses should have been lower than 2 M-circle
dot. It appears that these models of stars of 2 3 M-circle dot are
producing too much Ne-22 in the stellar surface at the end of the AGB.
On the other hand, the comparison with another set of stellar evolution
models with a different treatment of convection and on the assumptions
about the overshoot of the convective core during the core H-burning
phase, provided there is reasonable agreement between the observed and
predicted N/O and Ne/H ratios if initial masses of more massive stars
are about 4 M
Filiaciones:
García-Rojas J.:
Instituto de Astrofísica de Canarias, La Laguna, Tenerife, 38205, Spain
Universidad de la Laguna, Dept. Astrofísica, La Laguna, Tenerife, 38206, Spain
Peña M.:
Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, Méx. D. F., México, 04510, Mexico
Flores-Durán S.:
Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, Méx. D. F., México, 04510, Mexico
Hernández-Martínez L.:
Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, Méx. D. F., México, 04510, Mexico
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apdo. Postal 70-543, Méx. D. F., México, 04510, Mexico
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