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 ∼ 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 ∼ 1, 200 K in 1998 August to ∼ 180 K 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 −5 M ⊙ 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 ∼ 16, 000 L ⊙ before declining to ∼ 3, 000 L ⊙ . There is evidence for weak 6-7 µm 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 ± 0.7, 14 times smaller than the Solar System value.