The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-yr 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 ~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 ~1200K in 1998 August to ~180K in 2016 July. The dust mass, assuming amorphous carbon, was ~5×10^(-10) M⊙ in 1998 August, and we estimate that the total dust mass was ∼2×10−5M⊙ by ∼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 ~16000L⊙ before declining to ~3000L⊙. There is evidence for weak 6-7μm 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 (C2H2). We use the former to determine the 12C/13C ratio to be 6.4+/-0.7, 14 times smaller than the Solar System value.