Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
2 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
3 Astronomy Department, University of Washington, Seattle, WA 98195, USA
4 Isaac Newton Group of Telescopes, Apart. de Correos 321, 38700 Santa Cruz de la Palma, Spain
Received: 20 December 2010
Accepted: 4 February 2011
Context. Understanding the formation of collimated outflows is one of the most debated and controversial topics in the study of the late stages of stellar evolution.
Aims. M 2–9 is an outstanding representative of extreme aspherical flows. It presents unique features such as a pair of high-velocity dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes. Their study provides important information on the nature of the poorly understood central source of M 2–9 and its nebula.
Methods. Imaging monitoring at sub-arcsec resolution of the evolution of the nebula in the past decade is presented. Spectroscopic data provide complementary information.
Results. We determine the proper motions of the dusty blobs, which infer a new distance estimate of 1.3 ± 0.2 kpc, a total nebular size of 0.8 pc, a speed of 147 km s-1, and a kinematical age of 2500 yr. The corkscrew geometry of the inner rotating pattern is confirmed and quantified. Different recombination timescales for different ions explain the observed surface brightness distribution. According to the images taken after 1999, the pattern rotates with a period of 92 ± 4 years. On the other hand, the analysis of images taken between 1952 and 1977 measures a faster angular velocity. If the phenomenon were related to orbital motion, this would correspond to a modest orbital eccentricity (e = 0.10 ± 0.05), and a slightly shorter period (86 ± 5 years). New features have appeared after 2005 on the west side of the lobes and at the base of the pattern.
Conclusions. The geometry and travelling times of the rotating pattern support our previous proposal that the phenomenon is produced by a collimated spray of high velocity particles (jet) from the central source, which excites the walls of the inner cavity of M 2–9, rather than by a ionizing photon beam. The speed of such a jet would be remarkable: between 11 000 and 16 000 km s-1. The rotating-jet scenario may explain the formation and excitation of most of the features observed in the inner nebula, with no need for additional mechanisms, winds, or ionization sources. All properties point to a symbiotic-like interacting binary as the central source of M 2–9. The new distance determination implies system parameters that are consistent with this hypothesis.
Key words: planetary nebulae: individual: M 2–9 / ISM: jets and outflows / stars: winds, outflows / binaries: symbiotic
Based on observations obtained at; the 2.6 Nordic Optical Telescope operated by NOTSA; the 2.5 m INT and 4.2 m WHT telescopes of the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias. Also based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 8773 and 9050.
Movie is only available in electronic form at http://www.aanda.org
© ESO, 2011