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Register a new userPhysical properties of the fluorine and neutron-capture element-rich PN Jonckheere 900
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We performed detailed spectroscopic analyses of a young C-rich planetary nebula (PN) Jonckheere900 (J900) in order to characterise the properties of the central star and nebula. Of the derived 17 elemental abundances, we present the first determination of eight elemental abundances. We present the first detection of the [F IV] 4059.9 A, [F V] 13.4 um, and [Rb IV] 5759.6 A lines in J900. J900 exhibits a large enhancement of F and neutron-capture elements Se, Kr, Rb, and Xe. We investigated the physical conditions of the H2 zone using the newly detected mid-IR H2 lines while also using the the previously measured near-IR H2 lines, which indicate warm (~670 K) and hot (~3200 K) temperature regions. We built the spectral energy distribution (SED) model to be consistent with all the observed quantities. We found that about 67 % of all dust and gas components (4.5x10^-4 Msun and 0.83 Msun, respectively) exists beyond the ionisation front, indicating critical importance of photodissociation regions in understanding stellar mass loss. The best-fitting SED model indicates that the progenitor evolved from an initially ~2.0 Msun star which had been in the course of the He-burning shell phase. Indeed, the derived elemental abundance pattern is consistent with that predicted by a asymptotic giant branch star nucleosynthesis model for a 2.0 Msun star with Z = 0.003 and partial mixing zone mass of 6.0x10^-3 Msun. Our study demonstrates how accurately determined abundances of C/F/Ne/neutron-capture elements and gas/dust masses help us understand the origin and the internal evolution of the PN progenitors.
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Nebular spectroscopy is a valuable tool for assessing the production of heavy elements by slow neutron(n)-capture nucleosynthesis (the s-process). Several transitions of n-capture elements have been identified in planetary nebulae (PNe) in the last few years, with the aid of sensitive high-resolution near-infrared spectrometers. Combined with optical spectroscopy, the newly discovered near-infrared lines enable more accurate abundance determinations than previously possible, and provide access to elements that had not previously been studied in PNe or their progenitors. Neutron-capture elements have also been detected in PNe in the Sagittarius Dwarf galaxy and in the Magellanic Clouds. In this brief review, I discuss developments in observational studies of s-process enrichments in PNe, with an emphasis on the last five years, and note some open questions and preliminary trends.
We present near-infrared spectra of ten planetary nebulae (PNe) in the Large and Small Magellanic Clouds (LMC and SMC), acquired with the FIRE and GNIRS spectrometers on the 6.5-m Baade and 8.1-m Gemini South Telescopes, respectively. We detect Se and/or Kr emission lines in eight of these objects, the first detections of n-capture elements in Magellanic Cloud PNe. Our abundance analysis shows large s-process enrichments of Kr (0.6-1.3 dex) in the six PNe in which it was detected, and Se is enriched by 0.5-0.9 dex in five objects. We also estimate upper limits to Rb and Cd abundances in these objects. Our abundance results for the LMC are consistent with the hypothesis that PNe with 2--3 M$_{odot}$ progenitors dominate the bright end of the PN luminosity function in young gas-rich galaxies. We find no significant correlations between s-process enrichments and other elemental abundances, central star temperature, or progenitor mass, though this is likely due to our small sample size. We determine S abundances from our spectra and find that [S/H] agrees with [Ar/H] to within 0.2 dex for most objects, but is lower than [O/H] by 0.2-0.4 dex in some PNe, possibly due to O enrichment via third dredge-up. Our results demonstrate that n-capture elements can be detected in PNe belonging to nearby galaxies with ground-based telescopes, allowing s-process enrichments to be studied in PN populations with well-determined distances.
We have carried out a detailed analysis of the interesting and important very young planetary nebula (PN) Hen3-1357 (Stingray Nebula) based on a unique dataset of optical to far-IR spectra and photometric images. We calculated the abundances of nine elements using collisionally excited lines (CELs) and recombination lines (RLs). The RL C/O ratio indicates that this PN is O-rich, which is also supported by the detection of the broad 9/18 um bands from amorphous silicate grain. The observed elemental abundances can be explained by asymptotic giant branch (AGB) nucleosynthesis models for initially 1-1.5 Msun stars with Z = 0.008. The Ne overabundance might be due to the enhancement of 22Ne isotope in the He-rich intershell. By using the spectrum of the central star synthesized by Tlusty as the ionization/heating source of the PN, we constructed the self-consistent photoionization model with Cloudy to the observed quantities, and we derived the gas and dust masses, dust-to-gas mass ratio, and core-mass of the central star. About 80 % of the total dust mass is from warm-cold dust component beyond ionization front. Comparison with other Galactic PNe indicates that Hen3-1357 is an ordinary amorphous silicate rich and O-rich gas PN. Among other studied PNe, IC4846 shows many similarities in properties of the PN to Hen3-1357, although their post-AGB evolution is quite different from each other. Further monitoring observations and comparisons with other PNe such as IC4846 are necessary to understand the evolution of Hen3-1357.
We present multi-configuration Breit-Pauli AUTOSTRUCTURE calculations of distorted-wave photoionization (PI) cross sections, and total and partial final-state resolved radiative recombination (RR) and dielectronic recombination (DR) rate coefficients for the first six ions of the trans-iron element Se. These calculations were motivated by the recent detection of Se emission lines in a large number of planetary nebulae. Se is a potentially useful tracer of neutron-capture nucleosynthesis, but accurate determinations of its abundance in photoionized nebulae have been hindered by the lack of atomic data governing its ionization balance. Our calculations were carried out in intermediate coupling with semi-relativistic radial wavefunctions. PI and recombination data were determined for levels within the ground configuration of each ion, and experimental PI cross-section measurements were used to benchmark our results. For DR, we allowed dn=0 core excitations, which are important at photoionized plasma temperatures. DR is the dominant recombination process for each of these Se ions at temperatures representative of photoionized nebulae (~10^4 K). To estimate the uncertainties of these data, we compared results from three different configuration-interaction expansions for each ion, and tested the sensitivity of the results to the radial scaling factors in the structure calculations. We find that the internal uncertainties are typically 30-50% for the direct PI cross sections and ~10% for the computed RR rate coefficients, while those for low-temperature DR can be considerably larger (from 15-30% up to two orders of magnitude) due to the unknown energies of near-threshold autoionization resonances. The results are suitable for incorporation into photoionization codes used to numerically simulate astrophysical nebulae, and will enable robust determinations of nebular Se abundances.
We present multi-configuration Breit-Pauli distorted-wave photoionization (PI) cross sections and radiative recombination (RR) and dielectronic recombination (DR) rate coefficients for the first six krypton ions. These were calculated with the AUTOSTRUCTURE code, using semi-relativistic radial wavefunctions in intermediate coupling. Kr has been detected in several planetary nebulae (PNe) and H II regions, and is a useful tracer of neutron-capture nucleosynthesis. PI, RR, and DR data are required to accurately correct for unobserved Kr ions in ionized nebulae, and hence to determine elemental Kr abundances. PI cross sections have been determined for ground configuration states of Kr^0--Kr^5+ up to 100 Rydbergs. Our Kr^+ PI calculations were significantly improved through comparison with experimental measurements. RR and DR rate coefficients were determined from the direct and resonant PI cross sections at temperatures (10^1--10^7)z^2 K, where z is the charge. We account for Delta n=0 DR core excitations, and find that DR is the dominant recombination mechanism for all but Kr^+ at photoionized plasma temperatures. Internal uncertainties are estimated by comparing results computed with three different configuration-interaction expansions for each ion, and by testing the sensitivity to variations in the orbital radial scaling parameters. The PI cross sections are generally uncertain by 30-50% near the ground state thresholds. Near 10^4 K, the RR rate coefficients are typically uncertain by <10%, while those of DR exhibit uncertainties of factors of 2 to 3, due to the unknown energies of near-threshold autoionizing resonances. With the charge transfer rate coefficients presented in the third paper of this series, these data enable robust Kr abundance determinations in photoionized nebulae for the first time.
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