Abundances of Mn, Co and Eu in a sample of 20 F–G disk stars: the influence of hyperfine structure splitting

¹ Observatório Nacional/MCT, Rua General José Cristino 77, 20921-400 Rio de Janeiro, RJ, Brazil e-mail: [epeloso;katia;licio]@on.br
² Observatório do Valongo/UFRJ, Ladeira do Pedro Antônio 43, 20080-090 Rio de Janeiro, RJ, Brazil e-mail: gustavo@ov.ufrj.br

Received: 16 March 2005
Accepted: 22 June 2005

Abstract

We present Mn, Co and Eu abundances for a sample of 20 disk F and G dwarfs and subgiants with metallicities in the range . We investigate the influence of hyperfine structure (HFS) on the derived abundances of Mn and Co by using HFS data from different sources in the literature, as well as calculated HFS from interaction factors A and B. Eu abundances were obtained from spectral synthesis of one line that takes into account HFS from a series of recent laboratory measurements. For the lines analysed in this study, we find that for manganese, the differences between abundances obtained with different HFSs are no greater than 0.10 dex. Our cobalt abundances are even less sensitive to the choice of HFS than Mn, presenting a 0.07 dex maximum difference between determinations with different HFSs. However, the cobalt HFS data from different sources are significantly different. Our abundance results for Mn offer an independent confirmation of literature results, favouring type Ia supernovae as the main nucleosynthesis site of Mn production, in contrast to trends of Mn versus metallicity previously reported in the literature. For Co, we obtain in the range and [Co/Fe] rising to a level of +0.2 when [Fe/H] decreases from -0.3 to -0.8, in disagreement with recent results in the literature. The observed discrepancies may be attributed to the lack of HFS in the works we used for comparison. Our results for Eu are in accordance with low-mass type II supernovae being the main site of the r-process nucleosynthesis.