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Astron. Astrophys. 329, L9-L12 (1998)

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Letter to the Editor

Weak emission line [WELS] central stars
of planetary nebulae are [WC]-PG1159 stars *

M.Parthasarathy 1, 2, A.Acker 1 and B.Stenholm 3

1 Observatoire de Strasbourg 11, rue de l'universite, F-67000 Strasbourg, France
2 Indian Institute of Astrophysics Koramangala, Bangalore - 560034, India
3 Lund Observatory, Box 43, S-22100 Lund, Sweden

Received 26 May 1997 / Accepted 25 September 1997


The characteristics of the spectra of weak emission line stars (WELS) are found to be very similar to that of [WC]-PG1159 and PG1159 objects. On the basis of the spectra we find 31 WELS central stars of planetary nebulae to be in fact [WC]-PG1159 stars. These stars mark the transition from the [WC] central stars of planetary nebulae to the PG1159 (pre-)white dwarfs. The evolutionary sequence appears to be [WC late ] - [WC early ] - WELS = [WC]-PG1159 - PG1159. The presence of nebulae and dust shells around these stars and also the significant percentage of [WC]-PG1159 stars among the [WC] central stars of PN indicates that late He-flash scenario may not be the principal mechanism for their post-AGB evolution towards the non-DA white dwarf stage.

We found 4 hybrid central stars. They display a HeII/CIV 4650 - 4686Å trough very similar to that of PG1159 stars. However, their spectra show stellar Balmer lines indicating that they are relatively hydrogen-rich in contrast to the PG1159 stars.

Key words: stars: post-AGB – stars: carbon – stars: evolution – ISM: planetary nebulae – stars: emission-line

* Based on observations obtained at the European Southern Observatory (ESO), La Silla, Chile

Send offprint requests to: M. Parthasarathy

© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997