BD+44 493: a ninth magnitude messenger from the early universe: carbon enhanced and beryllium poor.
ITO H., AOKI W., HONDA S. and BEERS T.C.
Abstract (from CDS):
We present a one-dimensional 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 asymptotic giant branch 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.
Galaxy: abundances - stars: abundances - stars: individual: BD+44 493 - stars: Population II