Bibcode
Magrini, L.; Perinotto, M.; Mampaso, A.; Corradi, R. L. M.
Bibliographical reference
Astronomy and Astrophysics, v.426, p.779-786 (2004)
Advertised on:
11
2004
Journal
Citations
31
Refereed citations
24
Description
Using spectroscopic data presented in Magrini et al. (cite{m03}), we
have analyzed with the photoionization code CLOUDY 94.00 (Ferland et al.
cite{ferland}) 11 Planetary Nebulae belonging to the spiral galaxy M
33. Central star temperatures and nebular parameters have been
determined. In particular the chemical abundances of He/H, O/H, N/H,
Ar/H, and S/H have been measured and compared with values obtained via
the Ionization Correction Factors (ICF) method, when available. Chemical
abundance relationships have been investigated; in particular, a
correlation between N/H and N/O similar to the Galactic one (Henry
cite{henry}), and a feeble anti-correlation between O/H and N/O have
been found. A gradient in O/H across the disc of M 33 is consistent with
the one found from H Ii regions in this galaxy (Vílchez et al.
cite{vilchez88}). Further studies in the outer parts of M 33 are
however needed to ascertain this point. The present result shows that
oxygen and helium abundances (with lower accuracy also nitrogen, argon
and sulphur) can be actually estimated from the brightest PNe of a
galaxy, even if the electron temperature cannot be measured. We also
found that the oxygen abundance is quite independent of the absolute
magnitude of the PN and consequently the brightest PNe are
representative of the whole PN population. This represents an important
tool for measuring the metallicity of galaxies at the time of the
formation of PNe progenitors.
Based on observations obtained at the 4.2 m WHT telescope operated on
the island of La Palma by the Isaac Newton Group in the Spanish
Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica
de Canarias.