BD +44 493: A Ninth Magnitude Messenger from the Early Universe; Carbon Enhanced and Beryllium Poor

TL;DR

This study analyzes the chemical composition of the extremely metal-poor, carbon-enhanced star BD +44 493, revealing insights into early universe stellar populations and the origin of its elemental abundances.

Contribution

First detailed chemical abundance analysis of a very bright, extremely metal-poor CEMP star, providing new constraints on early supernovae and stellar evolution models.

Findings

BD +44 493 is a CEMP-no star with [Fe/H]=-3.7.

The star's low beryllium abundance supports the trend of decreasing Be with lower [Fe/H].

First Be measurement in a CEMP star, showing high C/O does not imply high Be.

Abstract

We present a 1D LTE chemical abundance analysis of the very bright (V=9.1) Carbon-Enhanced Metal-Poor (CEMP) star BD +44 493, based on high-resolution, high signal-to-noise spectra obtained with Subaru/HDS. The star is shown to be a subgiant with an extremely low iron abundance ([Fe/H]=-3.7), while it is rich in C ([C/Fe]=+1.3) and O ([O/Fe]=+1.6). Although astronomers have been searching for extremely metal-poor stars for decades, this is the first star found with [Fe/H]<-3.5 and an apparent magnitude V<12. Based on its low abundances of neutron-capture elements (e.g., [Ba/Fe]=-0.59), BD +44 493 is classified as a "CEMP-no" star. Its abundance pattern implies that a first-generation faint supernova is the most likely origin of its carbon excess, while scenarios related to mass loss from rapidly-rotating massive stars or mass transfer from an AGB companion star are not favored. From a high-quality spectrum in the near-UV region, we set an very low upper limit on this star's beryllium abundance (A(Be)=log(Be/H)+12<-2.0), which indicates that the decreasing trend of Be abundances with lower [Fe/H] still holds at [Fe/H]<-3.5. This is the first attempt to measure a Be abundance for a CEMP star, and demonstrates that high C and O abundances do not necessarily imply high Be abundances.