@inproceedings{ReimerAharonianHintonetal.2007,
  author    = {Reimer, O. and Aharonian, Felix A. and Hinton, J. and Hofmann, W. and Hoppe, S. and Raue, M. and Reimer, A.},
  title     = {VHE gamma-rays from Westerlund 2 and implications for the inferred energetics},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18172},
  year      = {2007},
  abstract  = {The H.E.S.S. collaboration recently reported the discovery of VHE γ-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR 20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gammaray luminosity of the order of 1035erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.},
  language  = {en}
}
@inproceedings{Hirschi2007,
  author    = {Hirschi, Raphael},
  title     = {The impact of reduced mass loss rates on the evolution of massive stars},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17616},
  year      = {2007},
  abstract  = {Mass loss is a very important aspect of the life of massive stars. After briefly reviewing its importance, we discuss the impact of the recently proposed downward revision of mass loss rates due to clumping (difficulty to form Wolf-Rayet stars and production of critically rotating stars). Although a small reduction might be allowed, large reduction factors around ten are disfavoured. We then discuss the possibility of significant mass loss at very low metallicity due to stars reaching break-up velocities and especially due to the metal enrichment of the surface of the star via rotational and convective mixing. This significant mass loss may help the first very massive stars avoid the fate of pair-creation supernova, the chemical signature of which is not observed in extremely metal poor stars. The chemical composition of the very low metallicity winds is very similar to that of the most metal poor star known to date, HE1327-2326 and offer an interesting explanation for the origin of the metals in this star. We also discuss the importance of mass loss in the context of long and soft gamma-ray bursts and pair-creation supernovae. Finally, we would like to stress that mass loss in cooler parts of the HR-diagram (luminous blue variable and yellow and red supergiant stages) are much more uncertain than in the hot part. More work needs to be done in these areas to better constrain the evolution of the most massive stars.},
  language  = {en}
}
@inproceedings{FullertonMassaPrinja2007,
  author    = {Fullerton, A. W. and Massa, D. L. and Prinja, R. K.},
  title     = {Revised mass-loss rates for O stars from the Pv resonance line},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17647},
  year      = {2007},
  abstract  = {The P v λλ1118, 1128 resonance doublet is an extraordinarily useful diagnostic of O-star winds, because it bypasses the traditional problems associated with determining mass-loss rates from UV resonance lines. We discuss critically the assumptions and uncertainties involved with using P v to diagnose mass-loss rates, and conclude that the large discrepancies between massloss rates determined from P v and the rates determined from "density squared" emission processes pose a significant challenge to the "standard model" of hot-star winds. The disparate measurements can be reconciled if the winds of O-type stars are strongly clumped on small spatial scales, which in turn implies that mass-loss rates based on Hα or radio emission are too large by up to an order of magnitude.},
  language  = {en}
}
@inproceedings{BouretLanzHillieretal.2007,
  author    = {Bouret, J.-C. and Lanz, T. and Hillier, D. J. and Foellmi, C.},
  title     = {Clumping in O-type Supergiants},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17662},
  year      = {2007},
  abstract  = {We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with Hα data. We have achieved an excellent match of the P V λλ1118, 1128 resonance doublet and N IV λ1718, as well as He II λ4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.},
  language  = {en}
}
@inproceedings{Gull2007,
  author    = {Gull, T. R.},
  title     = {Eta Carinae viewed from different vantages},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18200},
  year      = {2007},
  abstract  = {The spatially-resolved winds of the massive binary, Eta Carinae, extend an arcsecond on the sky, well beyond the 10 to 20 milliarcsecond binary orbital dimension. Stellar wind line profiles, observed at very different angular resolutions of VLTI/AMBER, HST/STIS and VLT/UVES, provide spatial information on the extended wind interaction structure as it changes with orbital phase. These same wind lines, observable in the starlight scattered off the foreground lobe of the dusty Homunculus, provide time-variant line profiles viewed from significantly different angles. Comparisons of direct and scattered wind profiles observed in the same epoch and at different orbital phases provide insight on the extended wind structure and promise the potential for three-dimensional imaging of the outer wind structures. Massive, long-lasting clumps, including the nebularWeigelt blobs, originated during the two historical ejection events. Wind interactions with these clumps are quite noticeable in spatially-resolved spectroscopy. As the 2009.0 minimum approaches, analysis of existing spectra and 3-D modeling are providing bases for key observations to gain further understanding of this complex massive binary.},
  language  = {en}
}
@inproceedings{Reimer2007,
  author    = {Reimer, A.},
  title     = {Clumping effects on non-thermal particle spectra in massive star systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-18246},
  year      = {2007},
  abstract  = {Observational evidence exists that winds of massive stars are clumped. Many massive star systems are known as non-thermal particle production sites, as indicated by their synchrotron emission in the radio band. As a consequence they are also considered as candidate sites for non-thermal high-energy photon production up to gamma-ray energies. The present work considers the effects of wind clumpiness expected on the emitting relativistic particle spectrum in colliding wind systems, built up from the pool of thermal wind particles through diffusive particle acceleration, and taking into account inverse Compton and synchrotron losses. In comparison to a homogeneous wind, a clumpy wind causes flux variations of the emitting particle spectrum when the clump enters the wind collision region. It is found that the spectral features associated with this variability moves temporally from low to high energy bands with the time shift between any two spectral bands being dependent on clump size, filling factor, and the energy-dependence of particle energy gains and losses.},
  language  = {en}
}
@inproceedings{SchnurrCrowther2007,
  author    = {Schnurr, O. and Crowther, P. A.},
  title     = {Mid-IR observations of WC stars, and the connection to wind clumping},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17884},
  year      = {2007},
  abstract  = {We present preliminary results of a tailored atmosphere analysis of six Galactic WC stars using UV, optical, and mid-infrared Spitzer IRS data. With these data, we are able to sample regions from 10 to 10³ stellar radii, thus to determine wind clumping in different parts of the wind. Ultimately, derived wind parameters will be used to accuratelymeasure neon abundances, and to so test predicted nuclear-reaction rates.},
  language  = {en}
}
@inproceedings{VinkBenagliaDaviesetal.2007,
  author    = {Vink, J. S. and Benaglia, P. and Davies, B. and de Koter, A. and Oudmaijer, R. D.},
  title     = {Advances in mass-loss predictions},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17948},
  year      = {2007},
  abstract  = {We present the results of Monte Carlo mass-loss predictions for massive stars covering a wide range of stellar parameters. We critically test our predictions against a range of observed massloss rates - in light of the recent discussions on wind clumping. We also present a model to compute the clumping-induced polarimetric variability of hot stars and we compare this with observations of Luminous Blue Variables, for which polarimetric variability is larger than for O and Wolf-Rayet stars. Luminous Blue Variables comprise an ideal testbed for studies of wind clumping and wind geometry, as well as for wind strength calculations, and we propose they may be direct supernova progenitors.},
  language  = {en}
}
@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{Sonneborn2007,
  author    = {Sonneborn, G.},
  title     = {Imaging and spectroscopy with the James Webb Space Telescope},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17983},
  year      = {2007},
  abstract  = {The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2013. JWST will find the first stars and galaxies that formed in the early universe, connecting the Big Bang to our own Milky Way galaxy. JWST will peer through dusty clouds to see stars forming planetary systems, connecting the MilkyWay to our own Solar System. JWST's instruments are designed to work primarily in the infrared range of 1 - 28 μm, with some capability in the visible range. JWST will have a large mirror, 6.5 m in diameter, and will be diffraction-limited at 2 μm (0.1 arcsec resolution). JWST will be placed in an L2 orbit about 1.5 million km from the Earth. The instruments will provide imaging, coronography, and multi-object and integral-field spectroscopy across the 1 - 28 μm wavelength range. The breakthrough capabilities of JWST will enable new studies of massive star winds from the Milky Way to the early universe.},
  language  = {en}
}