The Strasbourg-ESO Catalogue
- R. Tylenda
Using spectroscopic observations taken at the Observatoire de Haute-Provence (France) and the Observatoire du mont Mégantic (Canada), we describe wind fluctuations in the [WC 8]-type central star of the planetary nebula NGC 40, HD 826, which was observed intensively during 22 nights. Moving features seen on the top of the C iiiλ5696 and C ivλλ5801/12 (+C iiiλ5826) 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 timescales 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 C iii 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 low-mass Wolf-Rayet stars. Especially impressive are the significantly larger observed maximum radial acceleration values of the blobs, compared to those already reported for massive WC 5–9, or low-mass [WC 9] stars. This is attributed to the very small stellar radius of HD 826. In addition the β velocity field is found to possibly underestimate the true gradient within the stellar wind flow. On the whole, the wind of HD 826 is highly stochastically variable on a very short time-scale. This supports a turbulent origin.