1. NASA Astrobiology Institute,
2. Department of Astronomy/Steward Observatory,
3. Arizona Radio Observatory, University of Arizona, 933 North Cherry Avenue
4. Department of Chemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, USA

Correspondence to: L. M. Ziurys^1,2,3,4 Correspondence and requests for materials should be addressed to L.M.Z. (Email: lziurys@as.arizona.edu).

Abstract

The interstellar medium is enriched primarily by matter ejected from old, evolved stars^{1, 2}. The outflows from these stars create spherical envelopes, which foster gas-phase chemistry^{3, 4, 5}. The chemical complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio⁶. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of molecules than their oxygen-rich analogues⁷. Here we report observations of molecules in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chemical compounds have been identified, including NaCl, PN, HNC and HCO⁺. From the spectral line profiles, the molecules can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulphur-bearing molecules (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO⁺ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chemically diverse as their carbon counterparts.

1. NASA Astrobiology Institute,
2. Department of Astronomy/Steward Observatory,
3. Arizona Radio Observatory, University of Arizona, 933 North Cherry Avenue
4. Department of Chemistry, University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721, USA

Correspondence to: L. M. Ziurys^1,2,3,4 Correspondence and requests for materials should be addressed to L.M.Z. (Email: lziurys@as.arizona.edu).

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