AN ELEMENTAL ASSAY of VERY, EXTREMELY, and ULTRA-METAL-POOR STARS

We present a high-resolution elemental-abundance analysis for a sample of 23 very metal-poor ([Fe/H] < -2.0) stars, 12 of which are extremely metal-poor ([Fe/H] < -3.0), and 4 of which are ultra-metal-poor ([Fe/H] < -4.0). These stars were targeted to explore differences in the abundance ratios for elements that constrain the possible astrophysical sites of element production, including Li, C, N, O, the α-elements, the iron-peak elements, and a number of neutron-capture elements. This sample substantially increases the number of known carbon-enhanced metal-poor (CEMP) and nitrogen-enhanced metal-poor (NEMP) stars - our program stars include eight that are considered "normal" metal-poor stars, six CEMP-no stars, five CEMP-s stars, two CEMP-r stars, and two CEMP-r/s stars. One of the CEMP-r stars and one of the CEMP-r/s stars are possible NEMP stars. We detect lithium for three of the six CEMP-no stars, all of which are Li.