The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective

Abstract

We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai's Object) over a $\sim 20$-year period, drawing on ground-, airborne- and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from $\sim 1200$K in 1998 August to $\sim 180$K in 2016 July. The dust mass, assuming amorphous carbon, was $\sim 5\times 10^{-10}$M${}_{\odot }$ in 1998 August, and we estimate that the total dust mass was $\sim 2\times 10^{-5}$M${}_{\odot }$ by $\sim 2016$. The appearance of a near infrared excess in 2008 suggests a new episode of (or renewed) mass loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to $\sim 16000$L${}_{\odot }$ before declining to $\sim 3000$L${}_{\odot }$. There is evidence for weak 6-7$\mu$m absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai's Object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C${}_2$H${}_2$). We use the former to determine the ${}^{12}$C/${}^{13}$C ratio to be $6.4\pm 0.7$, 14 times smaller than the Solar System value.

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• The most variable VVV sources: eruptive protostars, dipping giants in the Nuclear Disc and others
• The Initial-Final Mass Relation for Hydrogen-Deficient White Dwarfs
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• Non-thermal radio emission in Sakurai's Object
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• Spectral variability of the born-again ejecta in A 58