P.R. Roelfsema 1, P. Cox 2, & J.-P. Baluteau 3
1 Space Research Organisation of the Netherlands, P.O. Box 800, NL-9700 AV Groningen, The Netherlands
2 Institut d'Astrophysique Spatiale, Bât. 121, Université de Paris XI, F-91405 Orsay, France
3 Laboratoire d'Astronomie Spatiale, CNRS, BP 8, F-13376, Marseille Cedex 12, France
In order to study the detailed distribution of galactic element abundances
infrared spectra from 2.5 to 196 
m were taken towards a sample of
50 compact and ultra compact HII regions using the two spectrographs
(LWS and SWS) on board ISO. The sample spans a large range in galactocentric
distance (0 to 25 kpc). The progress in this work will be presented.
The SWS-LWS spectra display significant variations from source to source in both spectral shape and content. The fine structure lines of O, N, Ne, Ar, S, C and Si are detected in most sources with some species (O, N, Ne, Ar) present in different stages of ionisation. The properties of the ionized gas such as the degree of ionization or the temperature can thus be precisely constrained leading to accurate determinations of the element abundances.
Results on the variation of various abundance indicators with galactocentric radius confirm that abundances decrease with increasing radius as reported in previous studies. The data suggest a flattening of the abundance gradients towards the galactic center.