The infrared view of dust and molecules around V4334 Sgr (Sakurai's
  Object): a 20-year 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 a $\sim20$-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 $\sim1200$K in 1998
August to $\sim180$K in 2016 July. The dust mass, assuming amorphous carbon,
was $\sim5\times10^{-10}$M$_\odot$ in 1998 August, and we estimate that the
total dust mass was $\sim2\times10^{-5}$M$_\odot$ by $\sim2016$. 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 $\sim16000$L$_\odot$
before declining to $\sim3000$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
$6.4\pm0.7$, 14 times smaller than the Solar System value.
