Common envelope evolution in born-again planetary nebulae -- Shaping the
  H-deficient ejecta of A30
  Born-again planetary nebulae (PNe) are extremely rare cases in the evolution
of solar-like stars. It is commonly accepted that their central stars (CSPN)
experienced a very late thermal pulse (VLTP), ejecting H-deficient material
inside the evolved H-rich PN. Given the short duration of this event and the
fast subsequent evolution of the CSPN, details of the mass ejection are
unknown. We present the first morpho-kinematic model of the H-deficient
material surrounding a born-again PN, namely A30. New San Pedro M\'{a}rtir
observations with the Manchester Echelle Spectrograph were recently obtained to
map its inner regions of A30 which are interpreted by means of the software
SHAPE in conjunction with HST WFC3 images. The SHAPE morpho-kinematic model
that best reproduces the observations is composed by a disrupted disk tilted
37$^\circ$ with respect to the line of sight and a pair of orthogonal opposite
bipolar ejections. We confirm previous suggestions that the structures closer
to the CSPN present the highest expansion velocities, that is, the disrupted
disk expands faster than the farther bipolar features. We propose that the
current physical structure and abundance discrepancy of the H-deficient clumps
around the CSPN of A30 can be explained by a common envelope (CE) phase
following the VLTP event. Our proposed scenario is also compared with other
known born-again PNe (A58, A78, HuBi1 and the Sakurai's Object).
