Deep high spectral resolution spectroscopy and chemical composition of
  ionized nebulae
  High spectral resolution spectroscopy has proved to be very useful for the
advancement of chemical abundances studies in photoionized nebulae, such as H
II regions and planetary nebulae (PNe). Classical analyses make use of the
intensity of bright collisionally excited lines (CELs), which have a strong
dependence on the electron temperature and density. By using high resolution
spectrophotometric data, our group has led the determination of chemical
abundances of some heavy element ions, mainly O++, O+ and C++ from faint
recombination lines (RLs), allowing us to deblend them from other nearby
emission lines or sky features. The importance of these lines is that their
emissivity depends weakly on the temperature and density structure of the gas.
The unresolved issue in this field is that recombination lines of heavy element
ions give abundances that are about 2-3 times higher than those derived from
CELs -in H II regions- for the same ion, and can even be a factor of 70 times
higher in some PNe. This uncertainty puts into doubt the validity of face
values of metallicity that we use as representative not only for ionized
nebulae in the Local Universe, but also for star-forming dwarf and spiral
galaxies at different redshifts. Additionally, high-resolution data can allow
us to detect and deblend faint lines of neutron capture element ions in PNe.
This information would introduce further restrictions to evolution models of
AGBs and would help to quantify the chemical enrichment in s-elements produced
by low and intermediate mass stars. The availability of an echelle spectrograph
at the E-ELT will be of paramount interest to: (a) extend the studies of heavy
element recombination lines to low metallicity objects, (b) to extend abundance
determinations of s-elements to planetary nebulae in the extragalactic domain
and to bright Galactic and extragalactic H II regions.
