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We present a brief review of the formation and evolution of hydrogen-deficient central stars of planetary nebulae. We include a detailed description of the main observable features of both the central stars and their surrounding nebulae and review their main classifications. We also provide a brief description of the possible progenitor systems of hydrogen-deficient central stars as well as of transients, which are closely connected to the formation of these stars. In particular, we offer a detailed theoretical explanation of the main evolutionary scenarios, both single and binary, which is devised to explain these stars and nebulae. Particular emphasis is made in the description of the so-called born again scenario, their quantitative predictions, and uncertainties. Finally, we discuss the pros and cons of both binary and single evolution channels, draw some conclusions, and discuss open questions in the field. [ABSTRACT FROM AUTHOR]

The nucleus of Hen 2-428 is a short orbital period (4.2 h) spectroscopic binary, whose status as potential supernovae type Ia progenitor has raised some controversy in the literature. We present preliminary results of a thorough analysis of this interesting system, which combines quantitative non-local thermodynamic (non-LTE) equilibrium spectral modelling, radial velocity analysis, multi-band light curve fitting, and state-of-the art stellar evolutionary calculations. Importantly, we find that the dynamical system mass that is derived by using all available He II lines does not exceed the Chandrasekhar mass limit. Furthermore, the individual masses of the two central stars are too small to lead to an SN Ia in case of a dynamical explosion during the merger process. [ABSTRACT FROM AUTHOR]