Abundances of metal-poor stars from SkyMapper

The targets were selected from the SkyMapper survey and include 90 objects with [Fe/H]<=-3 of which some 15 have [Fe/H]<=-3.5. When combining the sample with our previous studies, we find that the metallicity distribution function has a power-law slope of {Delta}(log N)/{Delta}[Fe/H] = 1.51 +/- 0.01 dex per dex over the range -4<=[Fe/H]<=-3.

With only seven carbon-enhanced metal-poor stars in the sample, we again find that the selection of metal-poor stars based on SkyMapper filters is biased against highly carbon-rich stars for [Fe/H]>-3.5. Of the 20 objects for which we could measure nitrogen, 11 are nitrogen-enhanced metal-poor (NEMP) stars. Within our sample, the high NEMP fraction (55 per cent +/- 21 per cent) is compatible with the upper range of predicted values (between 12 per cent and 35 per cent).