Issue |
A&A
Volume 403, Number 2, May IV 2003
|
|
---|---|---|
Page(s) | 659 - 673 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20030391 | |
Published online | 06 May 2003 |
Quantitative classification of WR nuclei of planetary nebulae *,**
1
Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
2
RSSD, ESTEC/ESA, Keplerlaan 1, 2201 AZ, Noordwijk ZH, The Netherlands
Corresponding author: A. Acker, acker@astro.u-strasbg.fr
Received:
30
October
2002
Accepted:
18
February
2003
We analyse 42 emission-line nuclei of Planetary Nebulae (PNe), in the
framework of a large spectrophotometric survey of [WC] nuclei of PNe conducted
since 1994, using low/medium resolution spectra obtained at ESO and at OHP.
We construct a grid of selected line-intensities (normalized to
-5806 Å = 100) ordered by decreasing ionisation potential
going from 871 to 24 eV. In this grid, the stars appear to belong clearly to prominent O (hot
[WO1-4] types) or C (cooler [WC4-11] types) line-sequences, in agreement with
the classification of massive WR stars applied to Central Stars of Planetary
Nebulae (CSPNe) by Crowther et al. [CITE] (CMB98).
We propose 20 selected line ratios and the FWHM of
and
lines as
classification diagnostics, which agree well with the 7 line ratios and the FWHM proposed
by CMB98. This classification based on
ionisation is related to the evolution of the temperature and of the stellar
wind, reflecting the mass-loss history.
In particular, inside the hot [WO4]-class, we discover four stars showing very
broad lines over the whole spectral range. These stars possibly mark the
transition from the initial momentum-driven phase to the later energy-driven
phase of the CSPNe along their evolution
from the post-Asymptotic Giant Branch (post-AGB) phase through [WC] late, [WC4] and [WO]-types.
The HR diagram and the diagram linking the terminal velocity and the
temperature indicate highly dispersed values of the stellar mass for our
sample, around a mean mass higher than for normal CSPNe.
The distribution of the 42 stars along the ionisation sequence shows 24% of
[WO1-3], 21% of [WO4], 17% of [WC4] hot stars, and 26% of [WC9-11] cool
stars. The [WC5-8] classes remain poorly represented (12%).
This distribution is confirmed on the basis of a large compilation of the
127 known emission-lines CSPNe, which represent about 5% of the known PNe.
Key words: planetary nebulae: general / stars: evolution / stars: AGB and post-AGB / stars: Wolf-Rayet / line: profiles
© ESO, 2003
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