73 research outputs found
Integrated fluxes for emission lines in the ultraviolet spectra of several planetaries
The IUE satellite observatory was used to obtain absolutely-calibrated emission line fluxes for diagnostic lines of multiply-ionized C, N, O, Si, Ne, and Ar which occur in the ultraviolet spectral region of planetary nebulae. These data, when combined with data from the blue, visual, and near infrared, provide improved estimates of ionic concentrations, plasma temperatures and densities, and elemental abundances
The physical parameters, excitation and chemistry of the rim, jets and knots of the planetary nebula NGC 7009
We present long-slit optical spectra along the major axis of the planetary
nebula NGC 7009. These data allow us to discuss the physical, excitation and
chemical properties of all the morphological components of the nebula,
including its remarkable systems of knots and jets. The main results of this
analysis are the following: i) the electron temperature throughout the nebula
is remarkably constant, T_e[OIII] = 10200K; ii) the bright inner rim and inner
pair of knots have similar densities of N_e = 6000cm^{-3}, whereas a much lower
density of N_e = 1500cm^{-3} is derived for the outer knots as well as for the
jets; iii) all the regions (rim, inner knots, jets and outer knots) are mainly
radiatively excited; and iv) there are no clear abundance changes across the
nebula for He, O, Ne, or S. There is a marginal evidence for an overabundance
of nitrogen in the outer knots (ansae), but the inner ones (caps) and the rim
have similar N/H values that are at variance with previous results. Our data
are compared to the predictions of theoretical models, from which we conclude
that the knots at the head of the jets are not matter accumulated during the
jet expansion through the circumstellar medium, neither can their origin be
explained by the proposed HD or MHD interacting-wind models for the formation
of jets/ansae, since the densities as well as the main excitation mechanisms of
the knots, disagree with model predictions.Comment: Figure 1 was changed because features were misidentified in the
previous version. 17 pages including 5 figures and 3 tables. ApJ in press.
Also available at http://www.iac.es/galeria/denise
A large-scale R-matrix calculation for electron-impact excitation of the Ne O-like ion
The five J levels within a or ground state complex provide
an excellent testing ground for the comparison of theoretical line ratios with
astrophysically observed values, in addition to providing valuable electron
temperature and density diagnostics. The low temperature nature of the line
ratios ensure that the theoretically derived values are sensitive to the
underlying atomic structure and electron-impact excitation rates. Previous
R-matrix calculations for the Ne O-like ion exhibit large spurious
structure in the cross sections at higher electron energies, which may affect
Maxwellian averaged rates even at low temperatures. Furthermore, there is an
absence of comprehensive excitation data between the excited states that may
provide newer diagnostics to compliment the more established lines discussed in
this paper. To resolve these issues, we present both a small scale 56-level
Breit-Pauli (BP) calculation and a large-scale 554 levels R-matrix Intermediate
Coupling Frame Transformation (ICFT) calculation that extends the scope and
validity of earlier JAJOM calculations both in terms of the atomic structure
and scattering cross sections. Our results provide a comprehensive
electron-impact excitation data set for all transitions to higher shells.
The fundamental atomic data for this O-like ion is subsequently used within a
collisional radiative framework to provide the line ratios across a range of
electron temperatures and densities of interest in astrophysical observations.Comment: 17 pages, 8 figure
Interactive simulated annealing for solving imprecise discrete multiattribute problems under risk
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