Computer Science
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000ign..confe..24g&link_type=abstract
Ionized Gaseous Nebulae. Mexico City November 21- 24, 2000, meeting abstract
Computer Science
Scientific paper
In the framework of our study of wind fluctuations in [WC 8--9]-type central stars of planetary nebulae, we describe spectroscopic observations taken at the Observatoire de Haute-Provence (France), Observatoire du mont Mégantic(Canada), and the European Southern Observatory (Chile). Moving features seen on the top of the CIII5696 and CIV5801/12 emission lines of HD 826 (=NGC 40) and BD +30 3639 are interpreted as outflowing clumps which are radially accelerated outwards in the Wolf-Rayet winds. The amplitudes of the variations range from ~ 5%, up to ~ 25-30% of the adjacent continuum flux, over timescales of hours. The blue-shifted absorption component of the lines exhibiting P-Cygni profiles is significantly more variable than the emission component, which suggests linear sizes for the clumps of ~1 R*. The subpeaks show large measurable velocity shifts during their lifetime: subpeaks (or gaps) on the top of the CIII line generally move towards the nearest line edge in a symmetric fashion in the blue and the red. Kinematic parameters of the blobs have been derived and compared to those observed for massive Wolf-Rayet stars: the wind fragmentation process appears as a purely atmospheric phenomenon, independent of the strong differences between both types of hot star. In addition, the β velocity field is found to possibly underestimate the true gradient within the stellar wind flow. On the whole, the winds are highly stochastically variable on a very short time-scale, which supports a turbulent origin. Unlike the ISM, we see clumps forming and dissipating in real time. The consequences of clumping in hot-star winds are manifold, including substantial constraints on the effective mass-loss rates, and their impact on the surrounding nebula itself.
Acker Agnés
Grosdidier Yves
Moffat Anthony F. J.
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