Temperature Fluctuations and Abundances in HiiGalaxies

There is evidence for temperature fluctuations in Planetary Nebulae and inGalactic HII regions. If such fluctuations occur in the low-metallicity,extragalactic HII regions used to probe the primordial helium abundance, thederived 4He mass fraction, Y_P, could be systematically different from the trueprimordial value. For cooler, mainly high-metallicity HII regions the derivedhelium abundance may be nearly unchanged but the oxygen abundance could havebeen seriously underestimated. For hotter, mainly low-metallicity HII regionsthe oxygen abundance is likely accurate but the helium abundance could beunderestimated. The net effect is to tilt the Y vs. Z relation, making itflatter and resulting in a higher inferred Y_P. Although this effect could belarge, there are no data which allow us to estimate the size of the temperaturefluctuations for the extragalactic HII regions. Therefore, we have exploredthis effect via Monte Carlos in which the abundances derived from a fiducialdata set are modified by \Delta-T chosen from a distribution with 0 < \Delta-T< \Delta-T_max where \Delta-T_max is varied from 500K to 4000K. It isinteresting that although this effect shifts the locations of the HII regionsin Y vs. O/H plane, it does not introduce any significant additionaldispersion.Comment: 11 pages, 9 postscript figures; submitted to the Ap