Bibcode
DOI
Esteban, Cesar; Vilchez, Jose M.
Bibliographical reference
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 390, no. 2, May 10, 1992, p. 536-540.
Advertised on:
5
1992
Journal
Citations
63
Refereed citations
50
Description
Results of a chemodynamical study of the W-R ring nebula NGC 6888 around
the WN6 star WR 136 are presented; the observations combine high spatial
and spectral resolution covering most of the optical range in different
zones of the nebula. The spectra show an emission system with three
different velocity components: -64 km/s, +78 km/s, and +18 km/s. The
first two correspond to the blue and redshifted parts of the shell, and
the third is associated with the ambient ionized gas. Diagnostic
diagrams indicate that the observed spectra are typical of purely
photoionized nebulae, without any significant contribution of shock
excitation. Chemical abundances of O/H, N/H, and He/H are derived for
each velocity component; it is shown that while the ambient gas has
nearly solar abundances, the expanding shell presents a remarkable O/H
deficiency and strong overabundances of N/H and He/H. It is concluded
that this nebula is composed mostly of stellar ejecta, possibly produced
by an event of very high mass loss or shell ejection at, or very near,
the RSG stage of the progenitor of WR 136 with an initial mass in the
range 25-40 solar masses.