Observations and three-dimensional ionization structure of the planetary nebula SuWt 2

Jul 10, 2013
18 pages
Published in:
  • Mon.Not.Roy.Astron.Soc. 434 (2013) 1513-1530
  • Published: Jul 10, 2013
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Abstract: (arXiv)
The planetary nebula SuWt 2 (PN G311.0+02.4), is an unusual object with a prominent, inclined central emission ellipse and faint bipolar extensions. It has two A-type stars in a proven binary system at the centre. However, the radiation from these two central stars is too soft to ionize the surrounding material leading to a so far fruitless search for the responsible ionizing source. Such a source is clearly required and has already been inferred to exist via an observed temporal variation of the centre-of-mass velocity of the A-type stars. Moreover, the ejected nebula is nitrogen-rich which raises question about the mass-loss process from a likely intermediate-mass progenitor. We use optical integral-field spectroscopy to study the emission lines of the inner nebula ring. This has enabled us to perform an empirical analysis of the optical collisionally excited lines, together with a fully three-dimensional photoionization modelling. Our empirical results are used to constrain the photoionization models, which determine the evolutionary stage of the responsible ionizing source and its likely progenitor. The time-scale for the evolutionary track of a hydrogen-rich model atmosphere is inconsistent with the dynamical age obtained for the ring. This suggests that the central star has undergone a very late thermal pulse. We conclude that the ionizing star could be hydrogen-deficient and compatible with what is known as a PG 1159-type star. The evolutionary tracks for the very late thermal pulse models imply a central star mass of ~ 0.64Mo, which originated from a ~ 3Mo progenitor. The evolutionary time-scales suggest that the central star left the asymptotic giant branch about 25,000 years ago, which is consistent with the nebula's age.
Note:
  • 18 pages, 11 figures, 10 tables, accepted for publication in MNRAS