The planetary nebula abell 48 and its [WN] nucleus

David J. Frew*, I. S. Bojičić, Q. A. Parker, M. Stupar, S. Wachter, K. DePew, A. Danehkar, M. T. Fitzgerald, D. Douchin

*Corresponding author for this work

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    27 Citations (Scopus)

    Abstract

    We have conducted a detailed multi-wavelength study of the peculiar nebula Abell 48 and its central star. We classify the nucleus as a helium-rich, hydrogen-deficient star of type [WN4-5]. The evidence for either a massive WN or a low-mass [WN] interpretation is critically examined, and we firmly conclude that Abell 48 is a planetary nebula (PN) around an evolved low-mass star, rather than a Population I ejecta nebula. Importantly, the surrounding nebula has a morphology typical of PNe, and is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. We estimate a distance of 1.6 kpc and a reddening, E(B-V) = 1.90 mag, the latter value clearly showing the nebula lies on the near side of the Galactic bar, and cannot be a massive WN star. The ionized mass (~0.3 M) and electron density (700 cm-3) are typical of middle-aged PNe. The observed stellar spectrum was compared to a grid of models from the Potsdam Wolf-Rayet (PoWR) grid. The best-fitting temperature is 71 kK, and the atmospheric composition is dominated by helium with an upper limit on the hydrogen abundance of 10 per cent. Our results are in very good agreement with the recent study of Todt et al., who determined a hydrogen fraction of 10 per cent and an unusually large nitrogen fraction of ~5 per cent. This fraction is higher than any other low-mass H-deficient star, and is not readily explained by current post-AGB models. We give a discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars. There is now tentative evidence for two distinct helium-dominated post-AGB lineages, separate to the helium-and carbon-dominated surface compositions produced by a late thermal pulse. Further theoretical work is needed to explain these recent discoveries.

    Original languageEnglish
    Article numberstu198
    Pages (from-to)1345-1364
    Number of pages20
    JournalMonthly Notices of the Royal Astronomical Society
    Volume440
    Issue number2
    DOIs
    Publication statusPublished - May 2014

    Keywords

    • abell 48
    • Planetary nebulae:general
    • Planetary nebulae:individual
    • Stars:evolution
    • Stars:wolf-rayet

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