Letter to the Editor

An occultation event in the nucleus of the planetary nebula M 2-29

¹ Centrum Astronomii UMK, ul.Gagarina 11, 87-100 Torun, Poland e-mail: [Marcin.Hajduk;Krzysztof.Gesicki]@astri.uni.torun.pl
² University of Manchester, School of Physics & Astronomy, Oxford Street, Manchester M13 9PL, UK e-mail: a.zijlstra@manchester.ac.uk

Received: 1 July 2008
Accepted: 9 September 2008

Abstract

Aims. 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.

Methods. We study the post-AGB central star of the (bipolar) Galactic bulge planetary nebula M 2-29. We have obtained additional HST imaging and SAAO spectroscopy of the object.

Results. 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 M 2-29 resembles the dust-occultation events seen in NGC 2346, and is modeled as an occultation by a circumbinary disk, where the binary period is 18 yr. Modulation during the decline shows evidence of another companion with a period of 23 days.

Conclusions. M 2-29 is the first eclipsing disk system among post-AGB stars. Close binaries with periods of around 1 month, as found in M 2-29, have been proposed to supply the energy needed to create the tori of bipolar planetary nebulae.