Journal Article

IC 4663: the first unambiguous [WN] Wolf–Rayet central star of a planetary nebula*

B. Miszalski, P. A. Crowther, O. De Marco, J. Köppen, A. F. J. Moffat, A. Acker and T. C. Hillwig

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 1, pages 934-947
Published in print June 2012 | ISSN: 0035-8711
Published online May 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20929.x
IC 4663: the first unambiguous [WN] Wolf–Rayet central star of a planetary nebula*

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We report on the serendipitous discovery of the first central star of a planetary nebula (PN) that mimics the helium- and nitrogen-rich WN sequence of massive Wolf–Rayet (WR) stars. The central star of IC 4663 (PN G346.2−08.2) is dominated by broad He ii and N v emission lines which correspond to a [WN3] spectral type. Unlike previous [WN] candidates, the surrounding nebula is unambiguously a PN. At an assumed distance of 3.5 kpc, corresponding to a stellar luminosity of 4000 L, the V= 16.9 mag central star remains 4–6 mag fainter than the average luminosity of massive WN3 stars even out to an improbable d= 8 kpc. The nebula is typical of PNe with an elliptical morphology, a newly discovered asymptotic giant branch (AGB) halo, a relatively low expansion velocity (vexp= 30 km s−1) and a highly ionized spectrum with an approximately solar chemical abundance pattern. The [WN3] star is hot enough to show Ne vii emission (T*= 140 ± 20 kK) and exhibits a fast wind (v= 1900 km s−1), which at d= 3.5 kpc would yield a clumped mass-loss rate of = 1.8 × 10−8 M yr−1 with a small stellar radius (R*= 0.11 R). Its atmosphere consists of helium (95 per cent), hydrogen (<2 per cent), nitrogen (0.8 per cent), neon (0.2 per cent) and oxygen (0.05 per cent) by mass. Such an unusual helium-dominated composition cannot be produced by any extant scenario used to explain the H-deficiency of post-AGB stars. The O(He) central stars share a similar composition and the discovery of IC 4663 provides the first evidence for a second He-rich/H-deficient post-AGB evolutionary sequence [WN] →O(He). This suggests that there is an alternative mechanism responsible for producing the majority of H-deficient post-AGB stars that may possibly be expanded to include other He-rich/H-deficient stars such as R Coronae Borealis stars and AM Canum Venaticorum stars. The origin of the unusual composition of [WN] and O(He) central stars remains unexplained.

Keywords: stars: abundances; stars: AGB and post-AGB; stars: mass-loss; stars: Wolf–Rayet; planetary nebulae: general; planetary nebulae: individual: PN G346.2−08.2

Journal Article.  9624 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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