Chemistry and physical properties of the born-again planetary nebula
  HuBi 1
  The central star of the planetary nebula (PN) HuBi\,1 has been recently
proposed to have experienced a very late thermal pulse (VLTP), but the dilution
of the emission of the recent ejecta by that of the surrounding H-rich old
outer shell has so far hindered confirming its suspected H-poor nature. We
present here an analysis of the optical properties of the ejecta in the
innermost regions of HuBi\,1 using MEGARA high-dispersion integral field and
OSIRIS intermediate-dispersion long-slit spectroscopic observations obtained
with the 10.4m Gran Telescopio de Canarias. The unprecedented tomographic
capability of MEGARA to resolve structures in velocity space allowed us to
disentangle for the first time the H$\alpha$ and H$\beta$ emission of the
recent ejecta from that of the outer shell. The recent ejecta is found to have
much higher extinction than the outer shell, implying the presence of large
amounts of dust. The spatial distribution of the emission from the ejecta and
the locus of key line ratios in diagnostic diagrams probe the shock excitation
of the inner ejecta in HuBi\,1, in stark contrast with the photoionization
nature of the H-rich outer shell. The abundances of the recent ejecta have been
computed using the {\sc mappings v} code under a shock scenario. They are found
to be consistent with a born-again ejection scenario experienced by the
progenitor star, which is thus firmly confirmed as a new "born-again" star.
