* Astronomy

Blobrana · L

RE: Abell 48

Blobrana · L

Title: Abell 48 - a rare WN-type central star of a planetary nebula
Authors: 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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Blobrana · L

Title: The planetary nebula Abell 48 and its [WN4] central star
Authors: I. S. Bojicic, D. J. Frew, Q. A. Parker, M. Stupar, S. Wachter, K. DePew

We have conducted a multi-wavelength study of the planetary nebula Abell 48 and give a revised classification of its nucleus as a hydrogen-deficient star of type [WN4]. The surrounding nebula has a morphology typical of PNe and importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. Indeed, no WN4 star is known to be surrounded by such a compact nebula. The ionised mass of the nebula is also a powerful discriminant between the low-mass PN and high-mass WR ejecta interpretations. The ionised mass would be impossibly high if a distance corresponding to a Pop I star was adopted, but at a distance of 2 kpc, the mass is quite typical of moderately evolved PNe. At this distance, the ionising star then has a luminosity of ~5000 Lsolar, again rather typical for a PN central star. We give a brief discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars.

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