Metal-poor stars identification method

We found a relation between the relative iron abundance and the flux-ratio of the Ca H&K region to that of the H{beta} line. This relation is temperature and surface gravity dependent, and it holds for stars with effective temperature 4800<=Teff<=6300K.

We applied it to noisy simulated synthetic spectra and inferred [Fe/H] with an uncertainty {sigma}<=0.65dex for -3.0<=[Fe/H]<=0.5 and G=15-17mag, which is sufficient for reliably identifying stars at [Fe/H]<-2.0. We predict that by selecting stars with inferred [Fe/H]<=-2.5dex, we can retrieve 80% of the stars with [Fe/H]<=-3.0, and we have a success rate of about 50%, i.e. 1 in 2 stars we select has [Fe/H]<=-3.0. We do not take into account the effect of reddening, so our method should only be applied to stars which are located in regions of low extinction.