TEMPERATURE-FLUCTUATIONS IN PHOTOIONIZED NEBULAE

Recombination lines in gaseous nebulae frequently yield parent-ion abu ndances that are several times larger than abundances derived from for bidden lines. One possible explanation for this discrepancy is the pre sence of temperature fluctuations. We examine temperature fluctuations in model nebulae by utilizing Peimbert's t(2) parameter. We have run large grids of models, varying the stellar temperature and the total h ydrogen density. We consider two abundance sets: The first uses ''typi cal'' planetary nebulae abundances, while the second examines the effe ct of increasing the metals and grains by a factor of 3. We also consi der both a constant density distribution and one which varies sinusoid ally with radius. We examine the method of deriving t(2) observational ly, which uses measured [O III] and Balmer temperatures. We find that this derived t(2) shows no correlation with the t(2) based on the inte gral definition. We discuss the reasons for this discrepancy, which in clude nonvalidity of some of the basic assumptions and theoretical and observational difficulties with the Balmer temperature. We find that, in high-metallicity objects especially, noncollisional contributions to [O III] lambda 24363 can significantly affect the derived temperatu re. We argue that while temperature fluctuations may result in non-neg ligible abundance corrections in some objects, they are insufficient t o resolve the abundance discrepancy.