2008A&A...490L...7H

Eclipses and occultations of post-AGB stars provide a powerful method of exploring the near-stellar environment, including close companions and circumstellar debris disks. Only six eclipsing systems and one dust-occultation system are currently known. New cases are important for our understanding of binary evolution during the AGB mass-loss phase. We study the post-AGB central star of the (bipolar) Galactic bulge planetary nebula M2-29. We have obtained additional HST imaging and SAAO spectroscopy of the object. The star showed a pronounced, long-lasting occultation with subsequent recovery. The event lasted almost 3 years, with a secondary minimum 9 years later. The photometric behavior of M2-29 resembles the dust-occultation events seen in NGC2346, and is modeled as an occultation by a circumbinary disk, where the binary period is 18yr. Modulation during the decline shows evidence of another companion with a period of 23 days. M2-29 is the first eclipsing disk system among post-AGB stars. Close binaries with periods of around 1 month, as found in M2-29, have been proposed to supply the energy needed to create the tori of bipolar planetary nebulae.