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.Comment: 13 pages, 4 tables, 5 figures. Accepted for publication in Ap

Nebular abundances of southern symbiotic stars

We have calculated relative elemental abundances for a sample of 43 symbiotic stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O were derived from new spectra collected in the optical range through low dispersion spectroscopy. The He ionic abundances were derived taking into account self-absorption effects in Balmer lines. We found that the symbiotic stars in the galactic bulge have heavy element abundances showing the same wide distribution as other bulge objects. In the galactic disk, the symbiotic stars follow the abundance gradient as derived from different kinds of objects.Comment: 12 pages, 6 figures, A&A - accepte

Fe I and Fe II Abundances of Solar-Type Dwarfs in the Pleiades Open Cluster

We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an equivalent width analysis of Fe I and Fe II lines in high-resolution spectra obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph. Abundances derived from Fe II lines are larger than those derived from Fe I lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and the discrepancy (deltaFe = [Fe II/H] - [Fe I/H]) increases dramatically with decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The Pleiades joins the open clusters M 34, the Hyades, IC 2602, and IC 2391, and the Ursa Major moving group, demonstrating ostensible over-ionization trends. The Pleiades deltaFe abundances are correlated with Ca II infrared triplet and Halpha chromospheric emission indicators and relative differences therein. Oxygen abundances of our Pleiades sample derived from the high-excitation O I triplet have been previously shown to increase with decreasing Teff, and a comparison with the deltaFe abundances suggests that the over-excitation (larger abundances derived from high excitation lines relative to low excitation lines) and over-ionization effects that have been observed in cool open cluster and disk field main sequence (MS) dwarfs share a common origin. Star-to-star Fe I abundances have low internal scatter, but the abundances of stars with Teff < 5400 K are systematically higher compared to the warmer stars. The cool star [Fe I/H] abundances cannot be connected directly to over-excitation effects, but similarities with the deltaFe and O I triplet trends suggest the abundances are dubious. Using the [Fe I/H] abundances of five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of [Fe/H] = +0.01 +/- 0.02.Comment: 32 pages, 7 figures, 7 tables; accepted by PAS

Connecting the primordial and Galactic deuterium abundances

The deuterium abundances inferred from observations of the interstellar medium within 1-2 kpc of the Sun range over a factor of three and the corresponding oxygen abundances show an even larger dispersion. While the lower D (and O) abundances likely result from depletion onto dust, the higher D abundances are consistent with the BBN-predicted primordial D abundance and chemical evolution models of the Galaxy with infall of primordial or nearly primordial material. The large ranges in deuterium and oxygen abundances suggest that the effects of depletion and/or infall have not been homogenized in the local interstellar medium.Comment: 5 pages, 4 figures; accepted for publication in MNRA

Ruthenium and hafnium abundances in giant and dwarf barium stars

We present abundances for Ru and Hf, compare them to abundances of other heavy elements, and discuss the problems found in determining Ru and Hf abundances with laboratory gf-values in the spectra of barium stars. We determined Ru and Hf abundances in a sample of giant and dwarf barium stars, by the spectral synthesis of two RuI (4080.574A and 4757.856A) and two HfII (4080.437A and 4093.155A) transitions. The stellar spectra were observed with FEROS/ESO, and the stellar atmospheric parameters lie in the range 4300 < Teff/K < 6500, -1.2 < [Fe/H] <= 0 and 1.4 <= log g < 4.6. The HfII 4080A and the RuI 4758A observed transitions result in a unreasonably high solar abundance, given certain known uncertainties, when fitted with laboratory gf-values. For these two transitions we determined empirical gf-values by fitting the observed line profiles of the spectra of the Sun and Arcturus. For the sample stars, this procedure resulted in a good agreement of Ru and Hf abundances given by the two available lines. The resulting Ru and Hf abundances were compared to those of Y, Nd, Sm and Eu. In the solar system Ru, Sm and Eu are dominated by the r-process and Hf, Nd and Y by the s-process, and all of these elements are enhanced in barium stars since they lie inside the s-process path. Ru abundances show large scatter when compared to other heavy elements, whereas Hf abundances show less scatter and closely follow the abundances of Sm and Nd, in good agreement with theoretical expectations. We also suggest a possible, unexpected, correlation of Ru and Sm abundances. The observed behaviour in abundances is probably due to variations in the 13C pocket efficiency in AGB stars, and, though masked by high uncertainties, hint at a more complex scenario than proposed by theory.Comment: 11 pages, 7 figures and 7 tables. accepted to A&

The Volatility Trend of Protosolar and Terrestrial Elemental Abundances

We present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and CI chondritic abundances. These new estimates indicate CI chondrites and solar abundances are consistent for 60 elements. We compare our new protosolar abundances with our recent estimates of bulk Earth composition (normalized to aluminium), thereby quantifying the devolatilization in going from the solar nebula to the formation of the Earth. The quantification yields a linear trend $\log(f) = \alpha\log(T_C) + \beta$, where $f$ is the Earth-to-Sun abundance ratio and $T_C$ is the 50$\%$ condensation temperature of elements. The best fit coefficients are: $\alpha = 3.676\pm 0.142$ and $\beta = -11.556\pm 0.436$. The quantification of these parameters constrains models of devolatilization processes. For example, the coefficients $\alpha$ and $\beta$ determine a critical devolatilization temperature for the Earth $T_{\mathrm{D}}(\mathrm{E}) = 1391 \pm 15$ K. The terrestrial abundances of elements with $T_{C} < T_{\mathrm{D}}(\mathrm{E})$ are depleted compared with solar abundances, whereas the terrestrial abundances of elements with $T_{C} > T_{\mathrm{D}}(\mathrm{E})$ are indistinguishable from solar abundances. The terrestrial abundance of Hg ($T_C$ = 252 K) appears anomalously high under the assumption that solar and CI chondrite Hg abundances are identical. To resolve this anomaly, we propose that CI chondrites have been depleted in Hg relative to the Sun by a factor of $13\pm7$. We use the best-fit volatility trend to derive the fractional distribution of carbon and oxygen between volatile and refractory components ($f_\mathrm{vol}$, $f_\mathrm{ref}$). We find ($0.91\pm 0.08$, $0.09 \pm 0.08$) for carbon and ($0.80 \pm 0.04$, $0.20 \pm 0.04$) for oxygen.Comment: Accepted for publication in Icarus. 28 pages, 12 figures, 5 tables. Compared to v1, the results and conclusion are the same, while discussion of results and implications is expanded considerabl

Planetary nebulae in the inner Milky Way: new abundances

The study of planetary nebulae in the inner-disk and bulge gives important information on the chemical abundances of elements such as He, N, O, Ar, Ne, and on the evolution of these abundances, which is associated with the evolution of intermediate-mass stars and the chemical evolution of the Galaxy. We present accurate abundances of the elements He, N, S, O, Ar, and Ne for a sample of 54 planetary nebulae located towards the bulge of the Galaxy, for which 33 have the abundances derived for the first time. The abundances are derived based on observations in the optical domain made at the National Laboratory for Astrophysics (LNA, Brazil). The data show a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to those works.Comment: Accepted for publication in RevMexAA (29 pages, 15 figures, 7 tables, uses rmaa.cls