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Heavy Element Abundances in Magellanic Cloud Planetary Nebulae

Presentation #351.03 in the session Planetary Nebulae, Supernova Remnants — iPoster Session.

Published onJun 29, 2022
Heavy Element Abundances in Magellanic Cloud Planetary Nebulae

We present an analysis of the heavy element compositions of the Magellanic Cloud planetary nebulae (PNe) SMP 29, SMP 73, and SMP 99 in the LMC, and SMC SMP 13, based on high-resolution near-infrared spectra. The observations were conducted with IGRINS (Park et al. 2014, SPIE, 9147, 91471D), a high-resolution (R = 45,000) H and K band spectrometer, on Gemini South. These observations aimed to detect emission lines of neutron(n)-capture elements (atomic number Z > 30), which can be produced by s-process nucleosynthesis in asymptotic giant branch (AGB) stars, the progenitors of PNe. The Magellanic Clouds are particularly valuable for studying AGB nucleosynthesis in low-metallicity populations with a range of initial stellar masses. The progenitor of LMC 29 may have been as massive as ~6 M, based on its large N/O ratio and low C abundance (Ventura et al. 2015, MNRAS, 452, 3679), while the other three are C-rich PNe produced by less massive stars. In the C-rich PNe, we detected emission lines of 3-5 n-capture elements (Se, Kr, Te, Rb, and Cd); in the fainter LMC 29 only Se and Kr were detected. Because only one ion of each element was observed, ionization correction factors (ICFs) must be applied to determine elemental abundances. To improve the accuracy of these ICFs, we recomputed light element abundances from published optical spectra (Leisy & Dennefeld 2006, A&A, 456, 451; Shaw et al. 2010, ApJ, 717, 562) using the ICF schema of Delgado-Inglada et al. (2014, MNRAS, 440, 536). We find that LMC 73 and 99 exhibit n-capture element abundances enhanced by factors of 5-20 relative to solar, depending on the choice of metallicity reference, and in SMC 13 Te is enriched while Se and Kr are not. LMC 29 shows no evidence for s-process enrichment, as has been found in Galactic PNe with relatively massive progenitors. We compare our abundances to theoretical predictions of AGB nucleosynthesis models (Karakas & Lugaro 2016, ApJ, 825, 26; Karakas et al. 2018, MNRAS, 477, 421). These results are part of a larger study of heavy element abundances in Magellanic Cloud PNe, which will help to address theoretical uncertainties in modeling low-metallicity AGB stars. We acknowledge support from NSF award AST 1715332.

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