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4.2. Key observational Requirements

By way of introduction to the data, we list some of the key goals of ongoing measurements of the primordial abundances.

  1. 4He : High accuracy, robust measurement in a few places with the lowest metal abundances.

  2. 3He : Measurement in gas with much lower metal abundances, or an understanding of stellar production and destruction and the results of all stars integrated over the history of the Galaxy (Galactic chemical evolution).

  3. D: The discovery of more quasar absorption systems with minimal H contamination.

  4. 7Li : Observations which determine the amount of depletion in halo stars, or which avoid this problem. Measurement of 6Li , Be and B to help estimate production prior to halo star formation, and subsequent depletion.

Since we are now obtaining ``precision'' measurements, it now seems best to make a few measurements with the highest possible accuracy and controls, in places with the least stellar processing, rather than multiple measurements of lower accuracy. We will now discuss observations of each of the nuclei, and especially D, in more detail.