Two's company, three's a crowd: SALT reveals the likely triple nature of
  the nucleus of the extreme abundance discrepancy factor planetary nebula Sp 3
  The substantial number of binary central stars of planetary nebulae (CSPNe)
now known ($\sim$50) has revealed a strong connection between binarity and some
morphological features including jets and low-ionisation structures. However,
some features and asymmetries might be too complex or subtle to ascribe to
binary interactions alone. A tertiary component, i.e. a triple nucleus, could
be the missing ingredient required to produce these features. The only proven
triple, NGC 246, is insufficient to investigate the shaping role of triple
nuclei, but one straight-forward way to identify more triples is to search for
binaries in nuclei with known visual companions. Here we report on the SALT HRS
discovery of a 4.81 d orbital period in the CSPN of Sp 3 which has a visual
companion 0.31" away. The spectroscopic distance of the visual companion agrees
with distance estimates to the nebula, the GAIA DR2 parallax of the central
star, and the gravity distance of the central star. This supports a physical
association between the visual companion and the 4.81 d binary, making the
nucleus of Sp 3 a likely triple. We determine $T_\mathrm{eff}=68^{+12}_{-6}$
kK, $\log g=4.6\pm0.2$ cm s$^{-2}$ and $v_\mathrm{rot}=80\pm20$ km s$^{-1}$ for
the primary from NLTE model atmosphere analysis. The peculiar nebula presents
an apparent bipolar morphology, jets and an unexpected `extreme' oxygen
abundance discrepancy factor (adf) of 24.6$^{+4.1}_{-3.4}$. The adf is
inconsistent with the purported trend for longer orbital period post-CE PNe to
exhibit normal adfs, further highlighting selection effects in post-CE PNe. The
Type-I nebular abundances of Sp 3, whose origin is often tied to more massive
progenitors, are incongruous with the likely Galactic Thick Disk membership of
Sp 3, possibly suggesting that rotation and binarity may play an important role
in the AGB nucleosynthesis of PNe. (abridged)
