Chemical Analysis of the Ninth Magnitude Carbon-Enhanced Metal-Poor Star BD+44 493

TL;DR

This study provides detailed chemical abundances for the extremely metal-poor star BD+44 493, suggesting its carbon enhancement likely originated from a faint supernova rather than binary transfer or massive star pollution.

Contribution

It offers new chemical abundance measurements for BD+44 493 and proposes a formation scenario involving a faint supernova, advancing understanding of CEMP-no star origins.

Findings

BD+44 493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant with carbon and oxygen excesses.

No significant nitrogen or neutron-capture element excesses were observed.

Li abundance is lower than the Spite plateau, and Be is very low, indicating limited Be production in progenitors.

Abstract

We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44 493, previously reported on by Ito et al. Our measurements confirm that BD+44 493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant star with excesses of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity have been found for this star. These results strongly suggest that the carbon enhancement in BD+44 493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H] < -6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a "faint" supernova, which underwent mixing and fallback, and only ejected small amounts of elements of metals beyond the lighter elements. The Li abundance of BD+44 493 (A(Li)=log(Li/H)+12=1.0) is lower than the Spite plateau value, as found in other metal-poor subgiants. The upper limit on Be abundance (A(Be)=log(Be/H)+12<-1.8) is as low as those found for stars with similarly extremely-low metallicity, indicating that the progenitors of carbon- (and oxygen-) enhanced stars are not significant sources of Be, or that Be is depleted in metal-poor subgiants with effective temperatures of ~5400K.