Detalles de publicación
PP 013062
Analysis of chemical abundances in planetary nebulae with [WC] central stars. II. Chemical abundances and the abundance discrepancy factor.
(1) IAC, Spain, (2) U. La Laguna, Spain, (3) IA-UNAM, Mexico, (4) PUC, Chile, (5) U. Chile
We present the abundance analysis of 12 planetary nebulae ionized by [WC] type stars and weak emission line stars (wels) obtained from high-resolution spectrophotometric data. Our main aims are to determine the chemical composition of the nebulae and to study the behaviour of the abundance discrepancy problem (ADF) in this type of planetary nebulae.
The detection of a large number of optical recombination lines (ORLs) and collisional excited lines (CELs) from different ions (O+, O++, C++, C+3 and Ne++) were presented in Garcia-Rojas et al. (2012). Most of the ORLs are reported for the first time in these PNe, increasing the sample of PNe with detected faint ORLs. Ionic abundances were determined from the available CELs
and ORLs, using previously determined physical conditions. Based on both sets of ionic abundances, we derived total chemical abundances in the nebulae using suitable ionization correction factors (when available).
In spite of the [WC] nature of the central stars, moderate ADF(O++), in the range from 1.2 to 4, were found for all the objects. We have found that, when the quality of the spectra is high enough, the ORLs O++/H+ abundance ratios obtained from different multiplets excited mainly by recombination are very similar. Possible dependence of ADFs with some nebular characteristics such as
surface brightness, nebular diameter and others, were analyzed, finding no correlation. Abundances derived from CELs were corrected by determining the t2 temperature fluctuation parameter. O abundances for PNe, derived from ORLs, are in general larger than the Solar abundance. We derived the C/O ratio from ORLs and N/O and alpha-element/O ratios from CELs and found that these PNe are, in
average, N-and C-richer than the average of large PN samples. About half of our sample is C-rich (C/O>1). The α-elements grow in lockstep with O abundance. Comparing the N/O and C /O ratios with those derived from stellar evolution models, we estimate that about half of our PNe have progenitors with initial masses similar or larger than 4 M_sol. No correlation was found between the stellar [WC] type and the nebular chemical abundances. A rough O abundance gradient computed for our limited PN sample, compared to the gradient given by H II regions, shows that there is a large dispersion in estimates of the PNe O abundance for a given Galactocentric distance. The PN gradient is flatter than the one for H II regions and at the solar distance and farther out, the PNe have larger O abundance than H II regions, similarly to what is found in other spiral galaxies. This fact has no convincing explanation so far.
The detection of a large number of optical recombination lines (ORLs) and collisional excited lines (CELs) from different ions (O+, O++, C++, C+3 and Ne++) were presented in Garcia-Rojas et al. (2012). Most of the ORLs are reported for the first time in these PNe, increasing the sample of PNe with detected faint ORLs. Ionic abundances were determined from the available CELs
and ORLs, using previously determined physical conditions. Based on both sets of ionic abundances, we derived total chemical abundances in the nebulae using suitable ionization correction factors (when available).
In spite of the [WC] nature of the central stars, moderate ADF(O++), in the range from 1.2 to 4, were found for all the objects. We have found that, when the quality of the spectra is high enough, the ORLs O++/H+ abundance ratios obtained from different multiplets excited mainly by recombination are very similar. Possible dependence of ADFs with some nebular characteristics such as
surface brightness, nebular diameter and others, were analyzed, finding no correlation. Abundances derived from CELs were corrected by determining the t2 temperature fluctuation parameter. O abundances for PNe, derived from ORLs, are in general larger than the Solar abundance. We derived the C/O ratio from ORLs and N/O and alpha-element/O ratios from CELs and found that these PNe are, in
average, N-and C-richer than the average of large PN samples. About half of our sample is C-rich (C/O>1). The α-elements grow in lockstep with O abundance. Comparing the N/O and C /O ratios with those derived from stellar evolution models, we estimate that about half of our PNe have progenitors with initial masses similar or larger than 4 M_sol. No correlation was found between the stellar [WC] type and the nebular chemical abundances. A rough O abundance gradient computed for our limited PN sample, compared to the gradient given by H II regions, shows that there is a large dispersion in estimates of the PNe O abundance for a given Galactocentric distance. The PN gradient is flatter than the one for H II regions and at the solar distance and farther out, the PNe have larger O abundance than H II regions, similarly to what is found in other spiral galaxies. This fact has no convincing explanation so far.