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TOPIC: IC 4663

Blobrana

L

Posts: 131433

Date: Oct 3 07:05 2012

IC 4663 Wolf-Rayet star	Permalink

Title: IC4663: the first unambiguous [WN] Wolf-Rayet central star of a planetary nebula Authors: Brent Miszalski (SAAO/SALT), Paul A. Crowther (Sheffield), Orsola De Marco (Macquarie), Joachim Köppen (Strasbourg), Anthony F. J. Moffat (Montréal/CRAQ), Agnès Acker (Strasbourg), Todd C. Hillwig (Valparaiso) Several [WC]-type central stars of planetary nebulae (PNe) are known to mimic the spectroscopic appearance of massive carbon-rich or WC-type Wolf-Rayet stars. In stark contrast, no [WN]-type central stars have yet been identified as clear-cut analogues of the common nitrogen-rich or WN-type Wolf-Rayet stars. We have identified the [WN3] central star of IC4663 to be the first unambiguous example in PNe. The low luminosity nucleus and an asymptotic giant branch (AGB) halo surrounding the main nebula prove the bona-fide PN nature of IC4663. Model atmosphere analysis reveals the [WN3] star to have an exotic chemical composition of helium (95%), hydrogen (O(He), that exists in parallel to the carbon-rich [WC]->PG1159 sequence. This suggests a simpler mechanism, perhaps a binary merger, can better explain H-deficiency in PNe and potentially other H-deficient/He-rich stars. In this respect IC4663 is the best supported case for a possible merged binary central star of a PN. Read more (792kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Mar 16 21:30 2012

IC 4663	Permalink

Title: IC 4663: The first unambiguous [WN] Wolf-Rayet central star of a planetary nebula Authors: B. Miszalski (SAAO/SALT), P. A. Crowther (Sheffield), O. De Marco (Macquarie), J. Köppen (Strasbourg/ISU/Kiel), A. F. J. Moffat (Montréal/CRAQ), A. Acker (Strasbourg), T. C. Hillwig (Valparaiso) 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 solar luminosity, 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 (v_exp=30 km/s) and a highly ionised 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_infty=1900 km/s), which at d=3.5 kpc would yield a clumped mass loss rate of solar mass = 1.8 x 10^-8 solar masses/yr with a small stellar radius (R_=0.11 solar radii). Its atmosphere consists of helium (95%), hydrogen (O(He). This suggests 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. Read more (1663kb, PDF) __________________

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