Analysis of chemical abundances in planetary nebulae with WC central stars II. Chemical abundances and the abundance discrepancy factorReportar como inadecuado




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Aims. We present the abundance analysis of 12 planetary nebulae ionized by WC-type stars and weak-emission-line stars welsobtained from high-resolution spectrophotometric data. Our main aims are to determine the chemical composition of the nebulae andto study the behaviour of the abundance discrepancy problem ADF in this type of planetary nebulae.Methods. The detection of a large number of optical recombination lines ORLs and collisionally excited lines CELs from differentions O+, O++, C++, C+3 and Ne++ were presented previously. Most of the ORLs were reported for the first time in these PNe, whichincreased the sample of PNe with detected faint ORLs. Ionic abundances were determined from the available CELs and ORLs, usingpreviously determined physical conditions. Based on these two sets of ionic abundances, we derived the total chemical abundances inthe nebulae using suitable ionization correction factors when available.Results. In spite of the WC nature of the central stars, moderate ADFO++ in the range from 1.2 to 4 were found for all theobjects. We found that when the quality of the spectra is high enough, the ORLs O++-H+ abundance ratios obtained from differentmultiplets excited mainly by recombination are very similar. Possible dependence of ADFs on some nebular characteristics such assurface brightness and nebular diameter were analysed, but we found no correlation. Abundances derived from CELs were correctedby determining the t2 temperature fluctuation parameter. O abundances for PNe, derived from ORLs, are in general higher than thesolar abundance. We derived the C-O ratio from ORLs and N-O and α-element-O ratios from CELs and found that these PNe are,on average, richer in N and C than the average of the large PN samples. About half of our sample is C-rich C-O > 1. The growthof α-elements is correlated with the O abundance. Comparing the N-O and C -O ratios with those derived from stellar evolutionmodels, we estimate that about half of our PNe have progenitors with initial masses similar to or larger than 4 M . No correlationwas found between the stellar WC type and the nebular chemical abundances. A rough O abundance gradient computed for ourlimited PN sample, compared with the gradient obtained for H ii regions, shows that there is a large dispersion in estimates of thePNe O abundance for a given Galactocentric distance. The PN gradient is flatter than that for H ii regions and at the solar distanceand farther out, the PNe have a higher O abundance than H ii regions, similarly to what is found in other spiral galaxies. This fact hasno convincing explanation so far.Nota general

Artículo de publicación ISI



Autor: García Rojas, Jorge; - Peña, Miriam; - Morisset, Christophe; - Delgado Inglada, Gloria; - Mesa Delgado, Adal; - Ruiz González,

Fuente: http://repositorio.uchile.cl/



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