Abundance analysis of barium and mild barium stars

Abstract

Aims. We compare and discuss abundances and trends in normal giants, mild barium, and barium stars, searching for differences and similarities between barium and mild barium stars that could help shed some light on the origin of these similar objects. Also, we search for nucleosynthetic effects possibly related to the s-process that were observed in the literature for elements like Cu in other types of s-process enriched stars. Methods. High signal to noise, high resolution spectra were obtained for a sample of normal, mild barium, and barium giants.Atmospheric parameters were determined from the Fe i and Fe ii lines. Abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, and Gd, were determined from equivalent widths and model atmospheres in a differential analysis, with the red giant Vir as the standard star. Results. The different levels of s-process overabundances of barium and mild barium stars were earlier suggested to be related to the stellar metallicity. Contrary to this suggestion, we found in this work no evidence of barium and mild barium having a different range in metallicity. However, comparing the ratio of abundances of heavy to light s-process elements, we found some evidence that they do not share the same neutron exposure parameter. The exact mechanism controlling this difference is still not clear. As a by-product of this analysis we identify two normal red giants misclassified as mild barium stars. The relevance of this finding is discussed. Concerning the suggested nucleosynthetic effects possibly related to the s-process, for elements like Cu, Mn, V and Sc, we found no evidence for an anomalous behavior in any of the s-process enriched stars analyzed here. However, further work is still needed since a clear [Cu/Fe] vs. [Ba/Fe] anticorrelation exists for other s-process enriched objects.

To Ba or not to Ba: Enrichment ins-process elements in binary systems with WD companions of various masses

“…ζ Cap and ζ Cyg. These stars were analysed by Smiljanic et al (2007). The agreement between the two studies on the s-process abundances is reasonable (in particular, both studies find large overabundances in ζ Cap and much milder ones in ζ Cyg), except for Sr in ζ Cap: Smiljanic et al (2007) Berdyugina (1994), Zacs et al (1997), and Barisevičius et al (2010) concluded, like we do, that DR Dra does not exhibit any s-process overabundance.…”

Mn, Cu, and Zn abundances in barium stars and their correlations with neutron capture elements

“…The stellar sample targeted in our study includes eight mild and classical barium stars and six normal giants of Smiljanic et al (2007), with a spectral S /N ratio ranging from 200 to 450 in the visible range. Smiljanic et al (2007) determined T eff , log g, and the metallicities from the simultaneous excitation and ionization equilibria of the equivalent widths of an average number of 120 Fe i and 12 Fe ii lines. Surface gravities were also computed from the stellar luminosities and theoretical HR diagrams, and a very good agreement was found for the two sets of gravities.…”

“…A summary of the stellar parameters is given in Table 1. The reader is referred to Smiljanic et al (2007) for a journal of the observations, details of derivation of atmospheric parameters, and the respective uncertainties.…”

“…In the present work we derived the abundances based on a spectrum synthesis for 14 stars that were previously analyzed by Smiljanic et al (2007). Although the focus of this paper is on performing relations between abundances of some iron peak and heavy elements, other elements than those discussed here are also shown in tables, in order to assemble all abundances determined so far for these stars in a single source, as explained in Sects.…”

“…Smiljanic et al (2007) and Allen & Barbuy (2006a) employ different methods to obtain the stellar atmospheric parameters T eff , log g, [Fe/H] and microturbulence, so we needed to establish a satisfactory consistence between the two sets of parameters, essentially the T eff scales. Smiljanic et al (2007) rely on the excitation and ionization equilibria of Fe i/Fe ii to derive the parameters self-consistently from the spectroscopic data alone, while Allen & Barbuy (2006a) derive T eff from photometry and the surface gravity from the stellar positions in the HR diagram. Allen & Barbuy (2006a), however, also obtain excitation and ionization T eff values, which agree well with the photometric ones.…”