Detalles de publicación
PP 015111
The PNe and H II regions in NGC6822 revisited. Hints on AGB nucleosynthesis
(1) IAC, Spain, (2) ULL, Spain, (3) IA-UNAM, Mexico, (4) ICN-UNAM, Mexico
The chemical behaviour of an ample sample of PNe in NGC6822 is analyzed. Spectrophotometric data of 11 PNe and two HII regions were obtained with the OSIRIS spectrograph attached to the Gran
Telescopio Canarias. Data for other 13 PNe and three HII 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 HII regions. 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 with metallicities similar to the values of HII 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 larger than 100,000 K. Possible bias 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 lower than 4 M sun, although if the comparison is made with Ne vs. O abundances, the initial masses should have been lower than 2 M sun. It appears that these models of stars of 2-
Telescopio Canarias. Data for other 13 PNe and three HII 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 HII regions. 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 with metallicities similar to the values of HII 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 larger than 100,000 K. Possible bias 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 lower than 4 M sun, although if the comparison is made with Ne vs. O abundances, the initial masses should have been lower than 2 M sun. It appears that these models of stars of 2-