A&A Supplement Series, Vol. 126, December I 1997, 297-310
Received July 29, 1996; accepted November 18, 1997
M.A. Ratag
- S.R. Pottasch
- M. Dennefeld 
- J. Menzies 
Send offprint request: S.R. Pottasch
Kapteyn Astronomical Institute, Gronin
gen University,
Postbus 800, 9700 AV Groningen, The Netherlands
Indonesian National Institute of
Aeronautics and Space (LAPAN),
Jakarta, Indonesia
Institut d'Astrophysique, 98bis B
oulevard Arago, F-75014 Paris,
France
South African Astronomical Observ
atory, P.O. Box 9, Cape Town,
South Africa
Abundance determinations of about 110 planetary nebulae, which are
likely to be in the Galactic Bulge are presented. Plasma diagnostics have
been performed by making use of the available forbidden line ratios
combined with radio continuum measurements. Chemical abundances of He,
O, N, Ne, S, Ar, and Cl are then derived by employing theoretical
nebular models as interpolation devices in establishing the ionization
correction factors (ICFs) used to estimate the distribution of atoms
among unobserved ionization stages. The overall agreement between the
results derived by using the model-ICFs and those obtained from the
theoretical models is reasonably good. The uncertainties related to the
total abundances show a clear dependence on the level of excitation. In
most cases, the abundances of chlorine can be derived only in objects
with a relatively high Cl-abundance. Contrary to the conclusion
previously drawn by Webster (1988), we found the excitation
classes are not uniformly distributed. A clear peak at about classes 5 and 6
is noticed. The distribution is shifted toward a lower excitation range
with respect to that of the nearby nebulae, reflecting the difference in
the central star temperature distribution between the two samples.
keywords: planetary nebulae -- ISM: abundances -- Galaxy: center