Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. II. Elemental Abundances

Abstract We present homogeneous abundance analysis of over 20 elements for 385 very metal-poor (VMP) stars based on the LAMOST survey and follow-up observations with Subaru Telescope. It is largest high-resolution VMP sample (including 363 new objects) studied by a single program, first attempt to accurately determine evolutionary stages such large Gaia parallaxes. The covers wide metallicity range from [Fe/H] ? ?1.7 down ? ?4.3, including 110 objects ? ?3.0. expanded coverage in status makes it possible define trends respectively giants turnoff stars. newly obtained data confirm most found previous studies, but also provide useful updates samples outliers. Li plateau seen main-sequence ?2.5 < our sample, whereas average clearly lower at metallicity. Mg, Si, Ca are overabundant respect Fe, showing decreasing trend increasing Comparisons chemical evolution models indicate that overabundance Ti, Sc, Co not well reproduced current theoretical predictions. Correlations between Sc ? -elements, while Zn shows detectable correlation only Ti other -elements. fraction carbon-enhanced ([C/Fe] > 0.7) 20%–30% depending treatment which C determined, much higher than (?8%). Twelve Mg-poor ([Mg/Fe] 0.0) have been identified ?3.8 through ?1.7. Eu-rich ([Eu/Fe] 1.0) discovered ?3.4 ?2.0, enlarging r -process-enhanced relatively high