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

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 an similar to 20-yr 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 similar to 1200 K in 1998 August to similar to 180 K in 2016 July, The dust mass, assuming amorphous carbon, was similar to 5 x 10(-10) M-circle dot in 1998 August, and we estimate that the total dust mass was similar to 2 x 10(-5) M-circle dot by similar to 2016, The appearance of a near-infrared excess in 2008 suggests that 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 similar to 16 000 L-circle dot before declining to similar to 3000 L-circle dot. 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 (C2H2). We use the former to determine the C-12/C-13 ratio to be 6.4 +/- 0.7, 14 times smaller than the Solar system value.