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We report optical long-slit spectra and direct imaging (ground-based and withHST) of the pre-planetary nebula (pPN) M2-56 obtained at different epochs. Theoptical nebula is composed by shock-excited material distributed in two pairsof nested lobes with different sizes and surface brightness. The compact,bright inner lobes (ILs) have an angular size of ~1.5"x1" each and displayclosed, bow-shaped ends. The extended, faint outer lobes (OLs), which enclosethe inner ones, have an agular size of ~13"x10". Within the ILs and the OLs thevelocity increases with the distance to the center, however, the ILs showexpansion velocities larger than the OLs. Consistent with the large speedsreached by the ILs (of up to ~350 km/s at the tips), we have measured theexpansive proper motions of the knots (~0.03 arcsec/yr) by comparing two-epochHST images. Moreover, we have discovered remarkable changes with time in thecontinuum and line emission spectrum of M2-56. In 1998, we detected a burst ofHalpha emission from the nebula nucleus that is interpreted as an indication ofa dense, fast (~350-500 km/s) bipolar wind from the nebula's core (referred toas "F1-wind"). Such a wind has been recently ejected (after 1989) probably as ashort-duration mass-loss event. Our data also reveal an optically thick,compact structure (cocoon?) and a HII region around the central star thatresult from further post-AGB mass-loss after the F1-wind. Recent brightening ofthe scattered stellar continuum as well as an increase of scattered Halphaemission along the lobes is reported, both results pointing to a decrease ofthe optical depth of the circumstellar material enshrouding the star. The datapresented here unveil the complex post-AGB mass-loss history of this object,whose rapid evolution is driven by multiple episodes of mass outflow, notregularly spaced in time... (abridged).

Fast, gusty winds blowing from the core of the pre-planetary nebula M2-56