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

Citation
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
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMY AND ASTROPHYSICS
ISSN journal
0004-6361 → ACNP
Volume
370
Issue
2
Year of publication
2001
Pages
513 - 523
Database
ISI
SICI code
0004-6361(200105)370:2<513:TOF[NO>2.0.ZU;2-1
Abstract
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.