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 ] \sim -2.3 ) 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 which extend to 3250 \AA .
These spectra show show that the most metal-poor and among the best-studied Galactic globular clusters show strong NH3360 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 , and well as related two of the three 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 .