Physical properties of the fullerene C60-containing planetary nebula
  SaSt 2-3
  We perform a detailed analysis of the fullerene C60-containing planetary
nebula (PN) SaSt2-3 to investigate the physical properties of the central star
(B0-1II) and nebula based on our own Subaru/HDS spectra and multiwavelength
archival data. By assessing the stellar absorption, we derive the effective
temperature, surface gravity, and photospheric abundances. For the first time,
we report time variability of the central star's radial velocity, strongly
indicating a binary central star. Comparison between the derived elemental
abundances and those predicted values by asymptotic giant branch (AGB) star
nucleosynthesis models indicates that the progenitor is a star with initial
mass of ~1.25 Msun and metallicity Z = 0.001/alpha-element/Cl-rich
([alpha,Cl/Fe] ~ +0.3-0.4). We determine the distance (11.33 kpc) to be
consistent with the post-AGB evolution of 1.25 Msun initial mass stars with Z =
0.001. Using the photoionisation model, we fully reproduce the derived
quantities by adopting a cylindrically shaped nebula. We derive the mass
fraction of the C-atoms present in atomic gas, graphite grain, and C60. The
highest mass fraction of C60 (~0.19%) indicates that SaSt2-3 is the C60-richest
PN amongst Galactic PNe. From comparison of stellar/nebular properties with
other C60 PNe, we conclude that the C60 formation depends on the central star's
properties and its surrounding environment (e.g., binary disc), rather than the
amount of C-atoms produced during the AGB phase.
