English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present new high-resolution chemical-abundance analyses for the well-knownhigh proper-motion subdwarfs G64-12 and G64-37, based on very highsignal-to-noise spectra (S/N ~ 700/1) with resolving power R ~ 95,000. Thesehigh-quality data enable the first reliable determination of the carbonabundances for these two stars; we classify them as carbon-enhanced metal-poor(CEMP) stars based on their carbonicities, which both exceed [C/Fe] = +1.0.They are sub-classified as CEMP- no Group-II stars, based on their location inthe Yoon-Beers diagram of absolute carbon abundance, A(C) vs. [Fe/H], as wellas on the conventional diagnostic [Ba/Fe]. The relatively low absolute carbonabundances of CEMP-no stars, in combination with the high effectivetemperatures of these two stars (Teff ~ 6500 K) weakens their CH molecularfeatures to the point that accurate carbon abundances can only be estimatedfrom spectra with very high S/N. A comparison of the observed abundancepatterns with the predicted yields from massive, metal-free supernova modelsreduces the inferred progenitor masses by factors of ~ 2-3, and explosionenergies by factors of ~ 10-15, compared to those derived using previouslyclaimed carbon abundance estimates. There are certainly many more warm CEMP-nostars near the halo main-sequence turnoff that have been overlooked in paststudies, directly impacting the derived frequencies of CEMP-no stars as afunction of metallicity, a probe that provides important constraints onGalactic chemical evolution models, the initial mass function in the earlyUniverse, and first-star nucleosynthesis.

G64-12 and G64-37 are Carbon-Enhanced Metal-Poor Stars