2003ApJ...598L.103L

Halo globular clusters pose four succinct issues that must be solved in any scenario of their formation: single-age, single-metallicity stellar populations; a lower limit ([Fe/H]~-2.5) to their average metallicity; comprising only 1% of the stellar halo mass; and being among the oldest stars in our Galaxy. New spectra are presented of Galactic stars and integrated spectra of Galactic globular clusters that extend to 3250 Å. These spectra show that the most metal-poor and among the best-studied Galactic globular clusters show strong NH 3360 Å absorption, even though their spectral energy distributions in the near-UV are dominated by blue horizontal-branch AF-type stars. These strong NH features must be coming from the main-sequence stars in these clusters. These new data are combined with existing data on the wide range of carbon and nitrogen abundance in very metal-poor ([Fe/H] < -3.5) halo giant and dwarf stars, together with recent models of zero-metal star formation, to make a strawman scenario for globular cluster formation that can reproduce three of the above four issues, as well as two of the three related issues pertaining to nitrogen overabundance. This strawman proposal makes observational and theoretical predictions that are testable, needing specific help from the modelers to understand all of the elemental constraints on globular cluster and halo formation.