OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. II. SPECTROSCOPY OF AN ULTRA METAL-POOR CEMP-no STAR*

Abstract

We report on the first high-resolution spectroscopic analysis of HE 0020–1741 , a bright ( V  = 12.9), ultra metal-poor ( = −4.1), carbon-enhanced ( = +1.7) star selected from the Hamburg/ESO Survey. This star exhibits low abundances of neutron-capture elements ( = −1.1) and an absolute carbon abundance A (C) = 6.1; based on either criterion, HE 0020–1741 is subclassified as a carbon-enhanced metal-poor star without enhancements in neutron-capture elements (CEMP-no). We show that the light-element abundance pattern of HE 0020–1741 is consistent with predicted yields from a massive ( M = ), primordial-composition, supernova (SN) progenitor. We also compare the abundance patterns of other ultra metal-poor stars from the literature with available measures of C, N, Na, Mg, and Fe abundances with an extensive grid of SN models (covering the mass range ), in order to probe the nature of their likely stellar progenitors. Our results suggest that at least two classes of progenitors are required at , as the abundance patterns for more than half of the sample studied in this work (7 out of 12 stars) cannot be easily reproduced by the predicted yields.