In January of 2015, Amanda Mashburn, a physics student conducting research with Dr. Nick Sterling, presented a poster and her research results at the 225th American Astronomical Society meeting in Seattle, Washington. Mrs. Mashburn is the first UWG student to present at a meeting of the American Astronomical Society, the winter meetings of which are among the largest gatherings of professional astronomers in the world.
In 2014, Mrs. Mashburn studied near-infrared observations of the Magellanic Clouds (satellite galaxies of the Milky Way) obtained with the 6.5-meter Baade Telescope in Chile. She analyzed emission lines of atoms and molecules in the spectra of planetary nebulae, the ejected outer layers of dying low-mass stars (up to eight times the sun's mass), to determine the chemical compositions of these objects. Selenium and krypton were detected in seven of the ten observed planetary nebulae, the first detection of either of these elements in the Magellanic Clouds. Elements heavier than zinc can be produced in low-mass giant stars before the planetary nebula stage. Despite the rarity of these elements, their abundances reveal a stunning amount of detail regarding the structure of giant stars, the star formation history of galaxies, and the production of carbon (a key ingredient for life!) in the universe. Amanda calculated the chemical composition of the Magellanic Cloud planetary nebulae, and is currently writing a journal article on the results that will be submitted to the high-impact "Astrophysical Journal."
The Detection of Neutron-Capture Elements in Magellanic Cloud Planetary Nebulae
A. Mashburn, N. C. Sterling, & I. U. Roederer
We present deep, high-resolution 0.8–2.5 µm spectra of ten Magellanic Cloud planetary nebulae (PNe). These data were obtained with the FIRE spectrometer (Simcoe et al. 2013, PASP, 125, 270) on the 6.5-m Baade Telescope at Las Campanas Observatory. The primary goal of these observations is to detect fine-structure emission lines of the neutron(n)- capture elements Se and Kr. These elements can be produced by s-process nucleosynthesis in thermally-pulsing asymptotic giant branch (AGB) stars, the progenitors of PNe, and are enriched along with carbon in AGB envelopes by convective dredge-up. Extragalactic PNe are particularly valuable for studying s-process enrichments, since their distances are welldetermined (unlike most Galactic PNe). Before our study, n-capture element detections had been reported in only one extragalactic PN, Hen 2-436 in the Sagittarius Dwarf (Wood et al. 2006, BAAS, 38, 1113; Otsuka et al. 2011, ApJ, 729, 39). Remarkably, we detect [Kr III] 2.199 and/or [Se IV] 2.287 µm in seven of the ten PNe (six of seven in the LMC and one of three in the SMC). At our resolution of R = 4800, these lines are resolved from nearby H2 lines and therefore are unaffected by blending. A preliminary abundance analysis indicates that several of these PNe exhibit s-process enrichments, as expected given their high C/O ratios. The well-known distances to the LMC and SMC allow s-process enrichment factors to be studied as a function of PN luminosity and potentially initial progenitor mass. Moreover, this sample will provide new insights into n-capture nucleosynthesis at low metallicities. Beyond the Se and Kr lines, the spectra are incredibly rich, with typically 100-200 emission lines detected in LMC PNe and up to 100 in SMC objects, including lines of H2, [P II], [S II], [S III], [Cl II], [Fe II], and a number of as yet unidentified features. Our results demonstrate the utility of nebular spectroscopy for studying n-capture nucleosynthesis in extragalactic environments.