2021RNAAS...5..287M

Cobalt abundances are rarely available for normal and Chemically Peculiar A stars because the strongest transitions of Co II and Co I lie in the mid-UV. The abundance of cobalt is derived for 21 Com using a mean mid-ultraviolet spectrum constructed by coadding 28 spectra collected with the Long Wave Prime camera over the 18 yr of the IUE mission. The strong transitions of Co II at 2286.16, 2307.86, 2324.32 and 2580.33 Å are present and usually blended. The least blended, λ 2286.16 Å, yields a mean overabundance of cobalt close to 10 times the solar abundance. Over the 24 hr 1991 monitoring of 21 Com, this line may have varied suggesting that cobalt may not be uniformly distributed over the surface of 21 Com.