2016/09/06 by Vinicius M. Placco, Timothy C. Beers, Henrique Reggiani +2 · 1 citation
Physics and Astronomy · #Absolute magnitude #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Carbon star #Galactic halo #Halo #Initial mass function #Spectral line #Stars #Stellar, planetary, and galactic studies #Supernova #astro-ph.SR
paper · pdf · doi:10.3847/2041-8205/829/2/l24
6 pages, 3 figures; accepted for publication in ApJ Letters. Corrected Ni abundances in Table 1
arxiv created 2016/09/06 · openalex created_date 2016/09/16 · openalex publication_date 2016/09/22 · arxiv updated 2016/10/05 · openalex updated_date 2026/08/06
ABSTRACT We present new high-resolution chemical-abundance analyses for the well-known high proper-motion subdwarfs G64-12 and G64-37, based on very high signal-to-noise ratio spectra ( ) with resolving power R ∼ 95,000. These high-quality data enable the first reliable determination of the carbon abundances for these two stars; we classify them as carbon-enhanced metal-poor (CEMP) stars based on their carboni cities, which both exceed [C/Fe] = +1.0. They are sub-classified as CEMP-no Group-II stars, based on their location in the Yoon–Beers diagram of absolute carbon abundance, A (C) versus [Fe/H], as well as on the conventional diagnostic [Ba/Fe]. The relatively low absolute carbon abundances of CEMP-no stars, in combination with the high effective temperatures of these two stars ( ), weakens their CH molecular features to the point that accurate carbon abundances can only be estimated from spectra with very high S/N. A comparison of the observed abundance patterns with the predicted yields from massive, metal-free supernova models reduces the inferred progenitor masses by factors of ∼2–3, and explosion energies by factors of ∼10–15, compared to those derived using previously claimed carbon-abundance estimates. There are certainly many more warm CEMP-no stars near the halo main-sequence turnoff that have been overlooked in past studies, directly impacting the derived frequencies of CEMP-no stars as a function of metallicity, a probe that provides important constraints on Galactic chemical evolution models, the initial mass function in the early universe, and first-star nucleosynthesis.