CHECKING THE VALIDITY OF BUSQUETS IONIZATION TEMPERATURE WITH DETAILED COLLISIONAL RADIATIVE MODELS

Busquet's RADIOM model for effective ionization temperature T-Z is an appealing and simple way to introduce non LTE effects in hydrocodes. W e report here checking the validity of RADIOM in the optically thin ca se by comparison with two collisional radiative models, MICCRON (level -by-level) for C and Al and SCROLL (superconfiguration-by-superconfigu ration) for Lu and Au. MICCRON is described in detail. The agreement b etween the average ion charge < Z > and the corresponding T-Z obtained from RADIOM on the one hand, and from MICCRON on the other hand for C and Al is excellent. The absorption spectra at T-Z agree very well wi th the one generated by SCROLL near LTE conditions (small beta). Farth er from LTE (large beta) the agreement is still good, but another effe ctive temperature gives an excellent agreement. It is concluded that t he model of Busquet is very good in most cases. There is however room for improvement when the departure from LTE is more pronounced for hea vy atoms and for emissivity. Improvement appears possible because the concept of ionization temperature seems to hold in a broader range of parameters. (C) 1997 Published by Elsevier Science Ltd. All rights res erved.