Y. Grosdidier et al., Turbulent outflows from [WC]-type nuclei of planetary nebulae II. The [WC 8] central star of NGC 40, ASTRON ASTR, 370(2), 2001, pp. 513-523
Using spectroscopic observations taken at the Observatoire de Haute-Provenc
e (France) and the Observatoire du mont Megantic (Canada), we describe wind
fluctuations in the [WC 8]-type central star of the planetary nebula NGC 4
0, HD 826, which was observed intensively during 22 nights. Moving features
seen on the top of the CIII lambda 5696 and CIV lambda lambda 5801/12 (+CI
II lambda 5826) emission lines are interpreted as outflowing "blobs" which
are radially accelerated outwards in the Wolf-Rayet wind. The amplitudes of
the variations range up to 25-30% of the adjacent continuum flux, over tim
escales of hours. The variabilities of both lines are quite well correlated
, although they are somewhat weaker for the C Iv complex. 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 were derived and compared to those observed for massive and other lo
w-mass Wolf-Rayet stars. Especially impressive are the significantly larger
observed maximum radial acceleration values of the blobs, compared to thos
e already reported for massive WC 5-9, or low-mass [WC 9] stars. This is at
tributed to the very small stellar radius of HD 826. In addition the beta v
elocity field is found to possibly underestimate the true gradient within t
he stellar wind flow. On the whole, the wind of HD 826 is highly stochastic
ally variable on a very short time-scale. This supports a turbulent origin.