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The authors investigated the metallicity distribution function (MDF) of the halo for field dwarf stars and for globular clusters. A significant improvement over earlier field-star samples has been achieved using the Carney-Latham survey of proper-motion stars, from which a halo sample has been isolated. The simple model of chemical evolution predicts slightly too many very metal-poor stars compared to the observed field stars. The metal-rich end of the MDF is investigated, and it is found that the field stars show a strong tail toward high metallicity not predicted by the simple model. This could result if the yield increased with metallicity, and several possible causes of such an increase are discussed.
Laird et al. (Thu,) studied this question.