Line temperatures and elemental abundances in HII galaxies

We present long-slit spectrophotometric observations in the red and near infrared of 12 HII galaxies. The spectral range includes the sulphur lines [SII] at λλ 6716, 6731 Å and [SIII] at λ 6312 Å and λλ 9069, 9532 Å. For all of the observed galaxies, at least three ion-weighted temperatures from forbidden auroral to nebular line ratios have been obtained and the relations between the different line temperatures have been discussed. It is found that, for some objects, the [OII] temperatures derived from those of [OIII] through the use of photo-ionisation models, without taking into account the effect of density, can lead to a significant underestimate of the O/H ionic abundance and hence of the total oxygen abundance. For all the observed objects, we have calculated the ionic abundances of O, O, S , S and N and they have been used to constraint the ionisation structure of the emmitting regions with the help of photo-ionisation models. From them, the ionisation correction factors for N and S, and their corresponding total abundances, have been derived.