Organic molecules, ions, and rare isotopologues in the remnant of the stellar-merger candidate, CK Vulpeculae (Nova 1670)

Abstract

CK Vul is a star whose outburst was observed in 1670-72. A stellar-merger event was proposed to explain its ancient eruption. Aims: We aim to investigate the composition of the molecular gas recently discovered in the remnant of CK Vul. Methods: We observed millimeter and submillimeter-wave spectra of CK Vul using the IRAM 30m and APEX telescopes. Radiative-transfer modeling of the observed molecular features was performed to yield isotopic ratios for various elements. Results: The spectra of CK Vul reveal a very rich molecular environment of low excitation ($T_{\mathrm{ex}}\lesssim$12 K). Atomic carbon and twenty seven different molecules, including two ions, were identified. They range from simple diatomic to complex polyatomic species of up to 7 atoms large. The chemical composition of the molecular gas is indicative of carbon and nitrogen-driven chemistry but oxides are also present. Additionally, the abundance of F may be enhanced. The spectra are rich in isotopologues that are very rare in most known sources. All stable isotopes of C, N, O, Si, and S are observed and their isotopic ratios are derived. Conclusions: The composition of the remnant's molecular gas is most peculiar and gives rise to a very unique millimeter and submillimeter spectrum. The observation of ions and complex molecules suggests the presence of a photoionizing source but its nature (a central star or shocks) remains unknown. The elemental and isotopic composition of the gas cannot be easily reconciled with standard nucleosynthesis but processing in hot CNO cycles and partial He burning can explain most of the chemical peculiarities. The isotopic ratios of CK Vul are remarkably close to those of presolar nova grains but the link of Nova 1670 to objects responsible for these grains is unclear.

arXiv commentaccepted to A&A; 16 pages plus extra figures and tables (68 total)

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• Radio Stars: from kHz to THz
• Molecular remnant of Nova 1670 (CK Vulpeculae): I. Properties and enigmatic origin of the gas
• Observational Constraints on the Common Envelope Phase
• Circumstellar ammonia in oxygen-rich evolved stars
• A "blue ring nebula" surrounding a thousands of years old stellar merger
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• Lithium in coalesced non-compact stars
• Molecules in the peculiar age-defying source IRAS 19312+1950
• Elemental abundances in the remnant of the ancient eruption of CK Vulpeculae
• A search for cool molecular gas in GK Persei and other classical novae
• Rotation-tunneling spectrum and astrochemical modeling of dimethylamine, CH${}_3$NHCH${}_3$, and searches for it in space
• The salty emission of the intermediate-mass AGB star OH 30.1 -0.7
• Identification of molecular line emission using Convolutional Neural Networks
• On the Nature of the Protoplanetary Nebula OH\,231.8+4.2
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