University of Minnesota
School of Physics & Astronomy

MN Institute for Astrophysics Colloquium

Friday, October 12th 2018
Speaker: Lucy Ziurys, University of Arizona
Subject: A Molecular View of the Late Stages of Stellar Evolution: Millimeter Observations of Supergiants and Planetary Nebulae

Molecular rotational lines, observed primarily at millimeter wavelengths, are unique probes of the environments around dying stars. They not only provide insight into the physics and chemistry of the stellar winds, but also can probe interior nucleosynthesis through isotopic composition. Using the millimeter/sub-mm telescopes of the Arizona Radio Observatory, we have been conducting extensive observations of molecular lines in the envelopes of supergiant/hypergiant stars, as well as in planetary nebulae. Our past work on supergiant VY Canis Majoris revealed a complex velocity structure with multiple, highly-collimated outflows, linked to known dust features. The molecular data confirm the occurrence of multiple, recent mass loss events. Our more recent study of NML Cygnus suggests a very similar mass loss scenario in the winds of this supergiant. In addition, the envelopes of both stars exhibit a unique chemistry with refractory oxides. Our very recent studies of planetary nebulae (PNe) show that these highly ionized objects are also rich in molecular material. Observations of over 20 different nebulae at various evolutionary stages reveal the presence of many polyatomic species such as HCN, HNC, CN, H2CO, CCH, and c-C3H2. Moreover, the abundances do not decrease with the age of the nebulae, and are in fact quite high in very old objects such as the Helix. These results suggest that PNe ejecta are at least partly molecular in content. Some of these nebulae also have enriched C, N, O isotopes. For example, K4-47 has 12C/13C = 2.0, 16O/17O = 21.4 and 14N/15N = 13.3, suggesting some explosive event at the end of the Asymptotic Giant Branch (AGB) phase. In addition, K4-47 appears to be contain many unidentified molecular lines – the target of laboratory spectroscopy studies that we also conduct to aid in our astrophysical interpretation.

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