@article{StastinskaGraefenerPenaetal.2004,
  author    = {Stastinska, G. and Gr{\"a}fener, G{\"o}tz and Pena, M. and Hamann, Wolf-Rainer and Koesterke, Lars and Szczerba, Ryszard},
  title     = {Comprehensive modelling of the planetary nebula LMC-SMP 61 and its [WC]-type central star},
  issn      = {0004-6361},
  year      = {2004},
  abstract  = {We present a comprehensive study of the Magellanic Cloud planetary nebula SMP 61 and of its nucleus, a Wolf- Rayet type star classified [WC 5-6]. The observational material consists of HST STIS spectroscopy and imaging, together with optical and UV spectroscopic data collected from the literature and infrared fluxes measured by IRAS. We have performed a detailed spectral analysis of the central star, using the Potsdam code for expanding atmospheres in non-LTE. For the central star we determine the following parameters: L-star = 10(3.96) L-., R-star = 0.42 R-., T-star = 87.5 kK, (M) over dot = 10(-6.12) M-. yr(-1), v(infinity) = 1400 km s(-1), and a clumping factor of D = 4. The elemental abundances by mass are X-He = 0.45, X-C = 0.52, X-N < 5 x 10(-5), X-O = 0.03, and X-Fe < 1 x 10(-4). The fluxes from the model stellar atmosphere were used to compute photoionization models of the nebula. All the available observations, within their error bars, were used to constrain these models. We find that the ionizing fluxes predicted by the stellar model are consistent with the fluxes needed by the photoionization model to reproduce the nebular emission, within the error margins. However, there are indications that the stellar model overestimates the number and hardness of Lyman continuum photons. The photoionization models imply a clumped density structure of the nebular material. The observed C III] lambda1909/C II lambda4267 line ratio implies the existence of carbon-rich clumps in the nebula. Such clumps are likely produced by stellar wind ejecta, possibly mixed with the nebular material. We discuss our results with regard to the stellar and nebular post-AGB evolution. The observed Fe-deficiency for the central star indicates that the material which is now visible on the stellar surface has been exposed to s-process nucleosynthesis during previous thermal pulses. The absence of nitrogen allows us to set an upper limit to the remaining H-envelope mass after a possible AGB final thermal pulse. Finally, we infer from the total amount of carbon detected in the nebula that the strong [WC] mass- loss may have been active only for a limited period during the post-AGB evolution},
  language  = {en}
}
@article{PenaHamannRuiz2003,
  author    = {Pena, M. and Hamann, Wolf-Rainer and Ruiz, M. T.},
  title     = {The LMC planetary nebula N66 revisited. Nebular kinematics and stellar models},
  isbn      = {1-583-81148-6},
  year      = {2003},
  language  = {en}
}
@phdthesis{HamannPenaGraefeneretal.2003,
  author    = {Hamann, Wolf-Rainer and Pena, M. and Gr{\"a}fener, G{\"o}tz and Ruiz, M. T.},
  title     = {The central star of the planetary nebula N66 in the Large Magellanic Cloud : a detailed analysis of its dramatic evolution 1983 - 2000},
  issn      = {0004-6361},
  year      = {2003},
  language  = {en}
}
@article{PenaHamann2003,
  author    = {Pena, M. and Hamann, Wolf-Rainer},
  title     = {The central star of the planetary nebula LMC-N66 : a massive accreting white dwarf?},
  year      = {2003},
  abstract  = {The central star of the PN LMC-N66 showed an impressive outburst in 1993 - 1994, returning to its initial conditions about 8 years later. Its spectrum resembles that of a WN4.5 star, being the only confirmed central star of planetary nebulae showing such a spectral type. Recent analysis for the central star parameters, performed by Hamann et al. (2003) is presented. They have found that the bolometric luminosity increased by a factor larger than 6, during the outburst. We discuss the possible scenarios which have been proposed to explain the exceptional stellar parameters and the outburst mechanism. The stellar characteristics and the morphology and kinematics of the planetary nebula suggest the presence of binary system (massive star with a less massive companion or, a white dwarf accreting matter in a close- binary system). These cases pose the least severe contradictions with observational constraints.},
  language  = {en}
}
@article{PenaStastinskaEstebanetal.1998,
  author    = {Pena, M. and Stastinska, G. and Esteban, C. and Koesterke, Lars and Medina, S. and Kingsburgh, R.},
  title     = {Galactic planetary nebulae with Wolf-Rayet nuclei : I. Objects with [WC]-early type stars},
  year      = {1998},
  language  = {en}
}
@article{PenaHamannKoesterkeetal.1997,
  author    = {Pena, M. and Hamann, Wolf-Rainer and Koesterke, Lars and Maza, J. and Mendez, R. H. and Peimbert, M. and Ruiz, M. T. and Torres-Peimbert, S.},
  title     = {HST spectrophotometric data of the central star of the planetary nebula LMC-N66},
  year      = {1997},
  language  = {en}
}
@article{PenaHamannKoesterkeetal.1997,
  author    = {Pena, M. and Hamann, Wolf-Rainer and Koesterke, Lars and Maza, J. and Mendez, R. H. and Peimbert, M. and Ruiz, M. T. and Torres-Peimbert, S.},
  title     = {Spectrophotometric data of the central star of the large magellanic cloud planetary nebula N66. Quantitative analysis of its WN type spectrum},
  year      = {1997},
  language  = {en}
}
@article{ReyesPerezMorissetPenaetal.2015,
  author    = {Reyes-P{\´e}rez, J. and Morisset, C. and Pena, M. and Mesa-Delgado, A.},
  title     = {A consistent spectral model of WR 136 and its associated bubble NGC 6888},
  series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  journal   = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-88274},
  pages     = {321 -- 324},
  year      = {2015},
  abstract  = {We analyse whether a stellar atmosphere model computed with the code CMFGEN provides an optimal description of the stellar observations of WR 136 and simultaneously reproduces the nebular observations of NGC 6888, such as the ionization degree, which is modelled with the pyCloudy code. All the observational material available (far and near UV and optical spectra) were used to constrain such models. We found that the stellar temperature T∗, at τ = 20, can be in a range between 70 000 and 110 000 K, but when using the nebula as an additional restriction, we found that the stellar models with T∗ ∼ 70 000 K represent the best solution for both, the star and the nebula.},
  language  = {en}
}
@article{PenaStastinskaEstebanetal.1999,
  author    = {Pena, M. and Stastinska, G. and Esteban, C. and Koesterke, Lars and Medina, S. and Kingsburgh, R.},
  title     = {Spectroscopy of planetary nebulae with [WR] nuclei},
  year      = {1999},
  language  = {en}
}