Article
IC 4663: the first unambiguous [WN] Wolf–Rayet central star of a planetary nebula
Monthly Notices of the Royal Astronomical Society
(2012)
Abstract
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, corre- sponding 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 asymp- totic giant branch (AGB) halo, a relatively low expansion velocity (vexp = 30kms−1) and a highly ionized spectrum with an approximately solar chemical abundance pattern. The [WN3] star is hot enough to show NeVII emission (T∗ = 140 ± 20kK) and exhibits a fast wind (v∞ = 1900 km s−1), which at d = 3.5 kpc would yield a clumped mass-loss rate of M ̇ = 1.8 × 10−8 M⊙ yr−1 with a small stellar radius (R∗ = 0.11 R⊙). Its atmosphere con- sists 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 pro- vides 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 pro- ducing 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 Venatico- rum 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
Disciplines
Publication Date
June, 2012
DOI
10.1111/j.1365-2966.2012.20929.x
Citation Information
B. Miszalski, P. A. Crowther, O. De Marco, J. Koppen, et al.. "IC 4663: the first unambiguous [WN] Wolf–Rayet central star of a planetary nebula" Monthly Notices of the Royal Astronomical Society Vol. 423 (2012) p. 934 - 947 Available at: http://works.bepress.com/todd_hillwig/12/