Abundances Of Galactic Planetary Nebulae Research Articles

Abundances of Planetary Nebulae and Evolved Stars: Iron and Sulfur Depletion, and Carbon and Nitrogen Enrichment, in Low- and Intermediate-mass Stellar Populations in the Milky Way

We research the elemental abundances in Galactic planetary nebulae (PNe) compared with those of their stellar progenitors (red giant branch and asymptotic giant branch, AGB, stars), to explore and quantify the expected—i.e., due to AGB evolution or condensation onto grains—differences. We gleaned the current literature for the nebular abundances while we used the APOGEE DR 17 survey data for the stellar sample. We examined the elements in common between the nebular and stellar samples, namely, C, N, O, Fe, and S. We confirm that iron in PNe is mostly entrapped in grains, with an average depletion 〈D[Fe/H]〉 = 1.741 ± 0.486 dex, and we disclose a weak correlation between iron depletion and the [O/H] abundance, D[Fe/H] = (6.6003 ± 2.443) × [O/H] + (1.972 ± 0.199). Sulfur may also be mildly depleted in PNe, with 〈D[S/H]〉 = 0.179 ± 0.291 dex. We also found an indication of nitrogen enrichment for PNe 〈E[N/H]〉 = 0.393 ± 0.421 dex, with maximum enrichment (0.980 ± 0.243) occurring for the PNe whose progenitors have gone through the hot-bottom burning. The carbon enrichment is 〈E[C/H]〉 = 0.337 ± 0.463 dex when measured for the general PN populations. Our results will be relevant for future Galactic and extragalactic studies comparing nebular and stellar samples.

Neon and Sulfur Abundances of Planetary Nebulae in the Magellanic Clouds

The chemical abundances of neon and sulfur for 25 planetary nebulae (PNe) in the Magellanic Clouds are presented. These abundances have been derived using mainly infrared data from the Spitzer Space Telescope. The implications for the chemical evolution of these elements are discussed. A comparison with similarly obtained abundances of Galactic PNe and HII regions and Magellanic Clouds HII regions is also given. The average neon abundances are 6.0x10(-5) and 2.7x10(-5) for the PNe in the Large and Small Magellanic Clouds respectively. These are ~1/3 and 1/6 of the average abundances of Galactic planetary nebulae to which we compare. The average sulfur abundances for the LMC and SMC are respectively 2.7x10(-6) and 1.0x10(-6). The Ne/S ratio (23.5) is on average higher than the ratio found in Galactic PNe (16) but the range of values in both data sets is similar for most of the objects. The neon abundances found in PNe and HII regions agree with each other. It is possible that a few (3-4) of the PNe in the sample have experienced some neon enrichment, but for two of these objects the high Ne/S ratio can be explained by their very low sulfur abundances. The neon and sulfur abundances derived in this paper are also compared to previously published abundances using optical data and photo-ionization models.

A reanalysis of chemical abundances in galactic PNe and comparison with theoretical predictions

New determinations of chemical abundances for He, N, O, Ne, Ar and S are derived for all galactic planetary nebulae (PNe) so far observed with a relatively high accuracy, in an effort to overcome differences in these quantities obtained over the years by different authors using different procedures. These include: ways to correct for interstellar extinction, the atomic data used to interpret the observed line fluxes, the model nebula adopted to represent real objects and the ionization corrections for unseen ions. A unique ‘good quality’ classical-type procedure, i.e. making use of collisionally excited forbidden lines to derive ionic abundances of heavy ions, has been applied to all individual sets of observed line fluxes in each specific position within each PN. Only observational data obtained with linear detectors, and satisfying some ‘quality’ criteria, have been considered. Such observations go from the mid-1970s up to the end of 2001. The observational errors associated with individual line fluxes have been propagated through the whole procedure to obtain an estimate of the accuracy of final abundances independent of an author's ‘prejudices’. Comparison of the final abundances with those obtained in relevant multi-object studies on the one hand allowed us to assess the accuracy of the new abundances, and on the other hand proved the usefulness of the present work, the basic purpose of which was to take full advantage of the vast amount of observations done so far of galactic PNe, handling them in a proper homogeneous way. The number of resulting PNe that have data of an adequate quality to pass the present selection amounts to 131. We believe that the new derived abundances constitute a highly homogeneous chemical data set on galactic PNe, with realistic uncertainties, and form a good observational basis for comparison with the growing number of predictions from stellar evolution theory. Owing to the known discrepancies between the ionic abundances of heavy elements derived from the strong collisonally excited forbidden lines and those derived from the weak, temperature-insensitive recombination lines, it is recognized that only abundance ratios between heavy elements can be considered as satisfactorily accurate. A comparison with theoretical predictions allowed us to assess the state of the art in this topic in any case, providing some findings and suggestions for further theoretical and observational work to advance our understanding of the evolution of low- and intermediate-mass stars.

Determination of the helium abundances in galactic planetary nebulae

We present the results of detailed studies on the He ionic abundances in galactic planetary nebulae. They are based on the newest emissivity data obtained by Benjamin et al. and take into account both the radiative transfer effects in the He I emission lines and the impact excitation of He and H atoms. The new values of the He +-to-H + and He-to-H ratios are obtained for different cases of He I line conjunctions.

Ionization-correction factors for the chemical composition determination of planetary nebulae with density gas fluctuations taking into account

270 photo ionization models of planetary nebulae luminescence was calculated. Free parameters for the models grid were energy distribution at the wavelengths 6912˚A, filling factor and chemical composition. T∗ and r∗ in models were selected from Blocker’s evolutional tracks. Energy distributions in nuclei radiation spectra at the wavelengths 6912˚A were taken from Clegg-Middlemass stellar atmosphere models, revised on the stellar wind presence. The nebular shell was assumed to be spherically-symmetrical. The radial distribution of nebular gas density was given by the empirical expression, which was derived by approximating surface brightness distribution for the real planetary nebulae. Density fluctuations were randomly imposed on this distribution. For the grid modeling we used the Cloudy 94 Ferland’s code. Obtained integrated spectra were analyzed, using common nebular gas diagnostic method. Relative abundances of different ions, calculated by this method, were used for determination of analytical expressions for ICFs. Under this spectra analysis the emission lines, for which the influence of density fluctuations may be neglected, were taken into account. As a result, new ICFs were found, and we would going to use these ICFs for obtaining chemical abundances of galactic planetary nebulae more exactly.

The features of chemical abundances in Galactic planetary nebulae

The chemical composition of 217 Galactic planetary nebulae is investigated; 203 of them are subdivided into four classes according to the masses of nebulae and progenitor stars. The values of local abundances, Galactic abundance gradients and Galactic electron temperature gradients are found for each class of nebula. The correlations between the abundances of pairs of elements are also calculated for each class of nebula. The results are compared with theoretical predictions. In particular, it is concluded that CN cycling can play a role in progenitor stars for all classes of planetary nebula