Turbulent outflows from [WC]-type nuclei of planetary nebulae. II. The [WC 8] central star of \object{NGC 40}.

Details Turbulent outflows from [WC]-type nuclei of planetary nebulae. II. The [WC 8] central star of \object{NGC 40}. Turbulent outflows from [WC]-type nuclei of planetary nebulae. II. The [WC 8] central star of \object{NGC 40}.

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...370..513g&link_type=abstract

Astronomy and Astrophysics, v.370, p.513-523 (2001)

Astronomy and Astrophysics

Astrophysics

12

Stars: Individual: Hd 826, Planetary Nebulae: Individual: Ngc 40, Stars: Mass-Loss, Stars: Atmospheres, Stars: Wolf-Rayet, Turbulence

Scientific paper

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 Iiilambda 5696 and C Ivlambda lambda 5801/12 (+C Iiilambda 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 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 beta 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. Based on observations taken at the Observatoire de Haute-Provence, France, and at the Observatoire du mont Mégantic, Canada.

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