@article{TodtKniazevGvaramadzeetal.2013,
  author    = {Todt, Helge Tobias and Kniazev, A. Y. and Gvaramadze, V. V. and Hamann, Wolf-Rainer and Buckley, D. and Crause, L. and Crawford, S. M. and Gulbis, A. A. S. and Hettlage, C. and Hooper, E. and Husser, T. -O. and Kotze, P. and Loaring, N. and Nordsieck, K. H. and O'Donoghue, D. and Pickering, T. and Potter, S. and Romero-Colmenero, E. and Vaisanen, P. and Williams, T. and Wolf, M.},
  title     = {Abell 48-a rare WN-type central star of a planetary nebula},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {430},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {3},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stt056},
  pages     = {2302 -- 2312},
  year      = {2013},
  abstract  = {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.},
  language  = {en}
}
@article{SurlanHamannAretetal.2013,
  author    = {Surlan, B. and Hamann, Wolf-Rainer and Aret, A. and Kubat, Jiř{\´i} and Oskinova, Lida and Torres, A. F.},
  title     = {Macroclumping as solution of the discrepancy between Ha and P v mass loss diagnostics for O-type stars},
  series = {ASTRONOMY \& ASTROPHYSICS},
  volume    = {559},
  journal   = {ASTRONOMY \& ASTROPHYSICS},
  publisher = {EDP SCIENCES S A},
  address   = {LES ULIS CEDEX A},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201322390},
  pages     = {17},
  year      = {2013},
  abstract  = {Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Ha emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from 04 to 07) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Ha emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Ha (and other Balmer and He II lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Ha and P v mass-loss diagnostics.},
  language  = {en}
}