Monthly Notices of the Royal Astronomical Society 434: 1513-1530 (2013)
doi: 10.1093/mnras/stt1116

Observations and three-dimensional ionization structure of the planetary nebula SuWt 2¹

A. Danehkar,$^{ 1}$ ² Q.A. Parker$^{ 1,2}$ and B. Ercolano$^{ 3,4}$
$^{1}$ Research Centre in Astronomy, Astrophysics & Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia
$^{2}$ Australian Astronomical Observatory, PO Box 296, Epping, NSW 1710, Australia
$^{3}$ Universitäts-Sternwarte München, Ludwig-Maxmilians Universität München, Scheinerstr. 1, D-81679 München, Germany
$^{4}$ Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany

Date: Accepted 2013 June 17. Received 2013 June 16; in original form 2013 March 20

Abstract:

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 $\sim 0.64 {\rm M}_{\bigodot}$ , which originated from a $\sim 3 {\rm M}_{\bigodot}$ 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.

Key words: ISM: abundances - planetary nebulae: individual: PN SuWt 2

Footnotes

... SuWt 2¹

Based on observations made with the ANU 2.3-m Telescope at the Siding Spring Observatory under programs 2090064 and 3120158.

...²

E-mail: ashkbiz . danehkar @ mq . edu . au