Thursday, January 10, 2013

1301.1944 (H. Todt et al.)

Abell 48 - a rare WN-type central star of a planetary nebula    [PDF]

H. Todt, A. Y. Kniazev, V. V. Gvaramadze, W. -R. Hamann, D. Buckley, L. Crause, S. M. Crawford, A. A. S. Gulbis, C. Hettlage, E. Hooper, T. -O. Husser, P. Kotze, N. Loaring, K. H. Nordsieck, D. O'Donoghue, T. Pickering, S. Potter, E. Romero-Colmenero, P. Vaisanen, T. Williams, M. Wolf
A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. Almost all of these H-deficient central stars (CSs) display spectra with strong carbon and helium lines. Most of them exhibit emission line spectra resembling those of massive WC stars. Therefore these stars are classed as CSPNe of spectral type [WC]. Recently, quantitative spectral analysis of two emission-line CSs, PB 8 and IC 4663, revealed that these stars do not belong to the [WC] class. Instead PB 8 has been classified as [WN/WC] type and IC 4663 as [WN] type. In this work we report the spectroscopic identification of another rare [WN] star, the CS of Abell 48. We performed a spectral analysis of Abell 48 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. We find that the expanding atmosphere of Abell 48 is mainly composed of helium (85 per cent by mass), hydrogen (10 per cent), and nitrogen (5 per cent). The residual hydrogen and the enhanced nitrogen abundance make this object different from the other [WN] star IC 4663. We discuss the possible origin of this atmospheric composition.
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