@inproceedings{MoffatHillierHamannetal.2007,
  author    = {Moffat, Anthony F. J. and Hillier, D. J. and Hamann, Wolf-Rainer and Owocki, S. P.},
  title     = {General Discussion},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17953},
  year      = {2007},
  abstract  = {Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007},
  language  = {en}
}
@inproceedings{LiermannHamann2007,
  author    = {Liermann, A. and Hamann, Wolf-Rainer},
  title     = {Clumping in Galactic WN stars : a comparison of mass loss rates from UV/optical \& radio diagnostics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17816},
  year      = {2007},
  abstract  = {The mass loss rates and other parameters for a large sample of Galactic WN stars have been revised by Hamann et al. (2006), using the most up-to date Potsdam Wolf-Rayet (PoWR) model atmospheres. For a sub-sample of these stars exist measurements of their radio free-free emission. After harmonizing the adopted distance and terminal wind velocities, we compare the mass loss rates obtained from the two diagnostics. The differences are discussed as a possible consequence of different clumping contrast in the line-forming and radio-emitting regions.},
  language  = {en}
}
@inproceedings{TodtHamannGraefener2007,
  author    = {Todt, Helge Tobias and Hamann, Wolf-Rainer and Gr{\"a}fener, G.},
  title     = {Clumping in [WC]-type Central Stars from electron-scattering line wings},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17711},
  year      = {2007},
  abstract  = {While there is strong evidence for clumping in the winds of massive hot stars, very little is known about clumping in the winds from Central Stars. We have checked [WC]-type CSPN winds for clumping by inspecting the electron-scattering line wings. At least for three stars we found indications for wind inhomogeneities.},
  language  = {en}
}
@inproceedings{FeldmeierHamannRaetzeletal.2007,
  author    = {Feldmeier, Achim and Hamann, Wolf-Rainer and R{\"a}tzel, D. and Oskinova, Lida},
  title     = {Hydrodynamic simulations of clumps},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17975},
  year      = {2007},
  abstract  = {Clumps in hot star winds can originate from shock compression due to the line driven instability. One-dimensional hydrodynamic simulations reveal a radial wind structure consisting of highly compressed shells separated by voids, and colliding with fast clouds. Two-dimensional simulations are still largely missing, despite first attempts. Clumpiness dramatically affects the radiative transfer and thus all wind diagnostics in the UV, optical, and in X-rays. The microturbulence approximation applied hitherto is currently superseded by a more sophisticated radiative transfer in stochastic media. Besides clumps, i.e. jumps in the density stratification, so-called kinks in the velocity law, i.e. jumps in dv/dr, play an eminent role in hot star winds. Kinks are a new type of radiative-acoustic shock, and propagate at super-Abbottic speed.},
  language  = {en}
}
@inproceedings{HamannOskinovaFeldmeier2007,
  author    = {Hamann, Wolf-Rainer and Oskinova, Lida and Feldmeier, Achim},
  title     = {Spectrum formation in clumpy stellar winds},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17838},
  year      = {2007},
  abstract  = {Modeling expanding atmospheres is a difficult task because of the extreme non-LTE situation, the need to account for complex model atoms, especially for the iron-group elements with their millions of lines, and because of the supersonic expansion. Adequate codes have been developed e.g. by Hillier (CMFGEN), the Munich group (Puls, Pauldrach), and in Potsdam (PoWR code, Hamann et al.). While early work was based on the assumption of a smooth and homogeneous spherical stellar wind, the need to account for clumping became obvious about ten years ago. A relatively simple first-order clumping correction was readily implemented into the model codes. However, its simplifying assumptions are severe. Most importantly, the clumps are taken to be optically thin at all frequencies ("microclumping"). We discuss the consequences of this approximation and describe an approach to account for optically thick clumps ("macroclumping"). First results demonstrate that macroclumping can generally reduce the strength of spectral features, depending on their optical thickness. The recently reported discrepancy between the Hα diagnostic and the Pv resonance lines in O star spectra can be resolved without decreasing the mass-loss rates, when macroclumping is taken into account.},
  language  = {en}
}
@inproceedings{OskinovaHamannFeldmeier2007,
  author    = {Oskinova, Lida and Hamann, Wolf-Rainer and Feldmeier, Achim},
  title     = {X-raying clumped stellar winds},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18133},
  year      = {2007},
  abstract  = {X-ray spectroscopy is a sensitive probe of stellar winds. X-rays originate from optically thin shock-heated plasma deep inside the wind and propagate outwards throughout absorbing cool material. Recent analyses of the line ratios from He-like ions in the X-ray spectra of O-stars highlighted problems with this general paradigm: the measured line ratios of highest ions are consistent with the location of the hottest X-ray emitting plasma very close to the base of the wind, perhaps indicating the presence of a corona, while measurements from lower ions conform with the wind-embedded shock model. Generally, to correctly model the emerging Xray spectra, a detailed knowledge of the cool wind opacities based on stellar atmosphere models is prerequisite. A nearly grey stellar wind opacity for the X-rays is deduced from the analyses of high-resolution X-ray spectra. This indicates that the stellar winds are strongly clumped. Furthermore, the nearly symmetric shape of X-ray emission line profiles can be explained if the wind clumps are radially compressed. In massive binaries the orbital variations of X-ray emission allow to probe the opacity of the stellar wind; results support the picture of strong wind clumping. In high-mass X-ray binaries, the stochastic X-ray variability and the extend of the stellar-wind part photoionized by X-rays provide further strong evidence that stellar winds consist of dense clumps.},
  language  = {en}
}