Bibcode
Esteban, C.; Mesa-Delgado, A.; Morisset, C.; García-Rojas, J.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 460, Issue 4, p.4038-4062
Advertised on:
8
2016
Número de citas
25
Número de citas referidas
20
Descripción
We present deep spectra of ring nebulae associated with Wolf-Rayet (WR)
and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW
52. The data have been taken with the 10m Gran Telescopio Canarias and
the 6.5m Clay Telescope. We extract spectra of several apertures in some
of the objects. We derive C2+ and O2+ abundances
from faint recombination lines in NGC 6888 and NGC 7635, permitting to
derive their C/H and C/O ratios and estimate the abundance discrepancy
factor (ADF) of O2+. The ADFs are larger than the typical
ones of normal H II regions but similar to those found in the ionized
gas of star-forming dwarf galaxies. We find that chemical abundances are
rather homogeneous in the nebulae where we have spectra of several
apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values
of electron temperature in a peripheral zone of NGC 6888, finding that
shock excitation can reproduce its spectral properties. We find that all
the objects associated with WR stars show N enrichment. Some of them
also show He enrichment and O deficiency as well as a lower Ne/O than
expected, this may indicate the strong action of the ON and NeNa cycles.
We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58
and S 308 with the nucleosynthesis predicted by stellar evolution models
of massive stars. We find that non-rotational models of stars of initial
masses between 25 and 40 M⊙ seem to reproduce the
observed abundance ratios of most of the nebulae.