Physical properties of the fullerene C60-containing planetary nebula SaSt2-3★

Abstract

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.