Observations and three-dimensional photoionization modelling of the Wolf-Rayet planetary nebula Abell 481

A. Danehkar,
Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia

H. Todt,
Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str.24/25, D-14476 Potsdam, Germany

B. Ercolano,
Universitäts-Sternwarte München, Ludwig-Maxmilians Universität München, Scheinerstr.1, D-81679 München, Germany
Exzellenzcluster Universe, Technische Universität München, Boltzmannstr.2, D-85748 Garching, Germany

A.Y. Kniazev
Universitäts-Sternwarte München, Ludwig-Maxmilians Universität München, Scheinerstr.1,South African Astronomical Observatory, PO Box 9, 7935 Observatory, Cape Town, South Africa
Southern African Large Telescope Foundation, PO Box 9, 7935 Observatory, Cape Town, South Africa

Date: Accepted 2014 January 28. Received 2014 January 28; in original form 2013 September 10


Recent observations reveal that the central star of the planetary nebula Abell 48 exhibits spectral features similar to massive nitrogen-sequence Wolf-Rayet stars. This raises a pertinent question, whether it is still a planetary nebula or rather a ring nebula of a massive star. In this study, we have constructed a three-dimensional photoionization model of Abell 48, constrained by our new optical integral field spectroscopy. An analysis of the spatially resolved velocity distributions allowed us to constrain the geometry of Abell 48. We used the collisionally excited lines to obtain the nebular physical conditions and ionic abundances of nitrogen, oxygen, neon, sulphur and argon, relative to hydrogen. We also determined helium temperatures and ionic abundances of helium and carbon from the optical recombination lines. We obtained a good fit to the observations for most of the emission-line fluxes in our photoionization model. The ionic abundances deduced from our model are in decent agreement with those derived by the empirical analysis. However, we notice obvious discrepancies between helium temperatures derived from the model and the empirical analysis, as overestimated by our model. This could be due to the presence of a small fraction of cold metal-rich structures, which were not included in our model. It is found that the observed nebular line fluxes were best reproduced by using a hydrogen-deficient expanding model atmosphere as the ionizing source with an effective temperature of $ T_{\rm eff}$ = 70kK and a stellar luminosity of $ L_{\rm\star}$ = 5500L $ _{\bigodot}$, which corresponds to a relatively low-mass progenitor star ($ \sim3$ M $ _{\bigodot}$) rather than a massive Pop I star.
Keywords: stars: Wolf-Rayet - ISM: abundances - planetary nebulae: individual: Abell48
Journal Reference: A. Danehkar, H. Todt, B. Ercolano, and A. Y. Kniazev. Monthly Notices of the Royal Astronomical Society, 439:3605-3615, 2014. doi:10.1093/mnras/stu203

Ashkbiz Danehkar