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1. Abundances of Iron-Group Elements in Planetary Nebulae and Consequences for Chemical Enrichment

   https://doi.org/10.1017/S1743921317000631  

   Dinerstein, Harriet L.; Geballe, T. R.; Sterling, N. C. (October 2016, Proceedings of the International Astronomical Union)

   Abstract We have developed a method for determining elemental Fe-group abundances in planetary nebulae using an infrared emission line of Zn, the least refractory Fe-group species. Many planetary nebulae, particularly those of the Milky Way’s thick disk and bulge, display subsolar [Fe/H] (as inferred from Zn) although their abundances of α elements such as O, S, and Ar are nearly solar. We discuss the implications for determining enhancements of species synthesized by the progenitor star during the AGB (e.g., s -process products), and for galactic chemical evolution in view of the metallicity dependence of AGB nucleosynthetic yields. 

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2. Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets

   https://doi.org/10.1017/s1743921322000278  

   Blackman, Eric G. (November 2020, Proceedings of the International Astronomical Union)

   Abstract Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally. 

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3. Neutron-Capture Element Abundances in Planetary Nebulae

   https://doi.org/10.3390/galaxies8020050  

   Sterling, N. C. (June 2020, Galaxies)

   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. 

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4. Carbon Isotope Ratios in Planetary Nebulae: The Unexpected Enhancement of 13C

   Ziurys, L.M.; Schmidt, D.R.; Woolf, N.J. (July 2020, The astrophysical journal)

   The 12C/13C ratio has been measured toward a sample of planetary nebulae (PNe) using millimeter observations of CO, HCN, HNC, CN, and other species, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The observed nebulae spanned the entire lifetime of PNe, from ∼900 to 12,000 yr, and include well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440, as well as relatively unexplored nebulae (M3–28, M2–48, and M3–55). In most cases, multiple molecules and transitions were used in the ratio determination, resulting in the most accurate values available to date, with 10%–40% uncertainties. The ratios found were unexpectedly low, lying in the range 12C/13C ∼1.0 ± 0.7–13.2 ± 4.9, with an average value of 3.7—drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Such low values are expected for the two O-rich nebulae studied (M2–9 and M2–48), because of insufficient third dredge-up events. However, most of the PNe observed were clearly carbon-rich, as deduced from the large number of C-bearing molecules present in them. Because nucleosynthesis ceases in the PN stage, both the C/O and the 12C/13C ratios must reflect abundances at the end of the AGB. These consistently low 12C/13C ratios, combined with the bipolar/multipolar morphologies of all planetary nebulae observed, suggest an explosive process involving proton-capture occurred at the AGB–PN transition. 

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5. MUSE crowded field 3D spectroscopy in NGC 300: IV. Planetary nebula luminosity function

   https://doi.org/10.1051/0004-6361/202244597  

   Soemitro, Azlizan A; Roth, Martin M; Weilbacher, Peter M; Ciardullo, Robin; Jacoby, George H; Monreal-Ibero, Ana; Castro, Norberto; Micheva, Genoveva (March 2023, Astronomy & Astrophysics)

   Aims.We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe. Methods.We analysed 44 fields observed with MUSE at the VLT, covering a total area of ∼11 kpc². We find [O III]λ5007 sources using the differential emission line filter (DELF) technique. We identified PNe through spectral classification with the aid of the BPT diagram. The PNLF distance was derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measured their extinction using the Balmer decrement. We estimated the luminosity and effective temperature of the central stars of the luminous PNe based on estimates of the excitation class and the assumption of optically thick nebulae. Results.We identify 107 PNe and derive a most-likely distance modulus $$ (m-M)_0 = 26.48^{+0.11}_{-0.26} $$ ($$ d = 1.98^{+0.10}_{-0.23} $$ Mpc). We find that the PNe at the PNLF cutoff exhibit relatively low extinction, with some high-extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses > 2.5 M_⊙but do not populate the PNLF cutoff. Conclusions.The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300. 

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