THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ –3.5, ,

Abstract

We present a homogeneous chemical abundance analysis of 16 elements in 190\nmetal-poor Galactic halo stars (38 program and 152 literature objects). The\nsample includes 171 stars with [Fe/H] < -2.5, of which 86 are extremely metal\npoor, [Fe/H] < -3.0. Our program stars include ten new objects with [Fe/H] <\n-3.5. We identify a sample of "normal" metal-poor stars and measure the trends\nbetween [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for\nthis sample. Using this mean trend, we identify objects that are chemically\npeculiar relative to "normal" stars at the same metallicity. These chemically\nunusual stars include CEMP-no objects, one star with high [Si/Fe], another with\nhigh [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than\nNa. The Sr and Ba abundances indicate that there may be two nucleosynthetic\nprocesses at lowest metallicity that are distinct from the main r-process.\nFinally, for many elements, we find a significant trend between [X/Fe] versus\nTeff which likely reflects non-LTE and/or 3D effects. Such trends demonstrate\nthat care must be exercised when using abundance measurements in metal-poor\nstars to constrain chemical evolution and/or nucleosynthesis predictions.\n