Abstract
ABSTRACT. The primordial abundance of 4He provides a crucial test of the consistency of the standard, hot big bang model of cosmology. To fully exploit the very high quality recent data on helium in extragalactic HII regions, it is crucial to reduce the current uncertainty in the correction which must be made for stellar produced 4He. Since carbon is produced (mainly) by intermediate mass stars (M<8 M@) and oxygen (mainly) by massive -and, therefore, very short-lived-stars (M> 8 M.), carbon should be a more reliable indicator of the level of chemical pollution by the debris of stellar evolution. In comparing Y with [C] =l04(C/H), it is found that: AY=-0.02[C]. For those HIl regions with [C] ,,,< 0.2 (such as the SMC), the correction to the primordial abundance is as small as or, smaller than, the other observational uncertainties. Current high quality data then suggests that the primordial mass fraction of 4He is: Yp = O.235tO. ("3a"); the implications of this result for cosmology and particle physics will be discussed.
