Bibcode
García-Rojas, J.; Peña, Miriam; Morisset, C.; Delgado-Inglada, Gloria; Mesa-Delgado, Adal; Ruiz, María Teresa
Referencia bibliográfica
Astronomy and Astrophysics, Volume 558, id.A122, 24 pp.
Fecha de publicación:
10
2013
Revista
Número de citas
60
Número de citas referidas
48
Descripción
Aims: 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. Methods: The detection of a large number of
optical recombination lines (ORLs) and collisionally excited lines
(CELs) from different ions (O+, O++,
C++, C+3 and Ne++) were presented
previously. Most of the ORLs were reported for the first time in these
PNe, which increased 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 these two sets of
ionic abundances, we derived the total chemical abundances in the
nebulae using suitable ionization correction factors (when available).
Results: 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 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 on some nebular characteristics
such as surface brightness and nebular diameter were analysed, but we
found 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 higher than the
solar 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 growth of
α-elements is correlated with the 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 to or larger than 4 M⊙. 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
with the gradient obtained for 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 that for H ii
regions and at the solar distance and farther out, the PNe have a higher
O abundance than H ii regions, similarly to what is found in other
spiral galaxies. This fact has no convincing explanation so far.
Based on data obtained at Las Campanas Observatory, Carnegie
Institution.
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