Analysis of 26 barium stars

I. Abundances

Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo, Brazil e-mail: [dinah;barbuy]@astro.iag.usp.br

Received: 25 January 2006
Accepted: 16 March 2006

Abstract

Context.We present a detailed analysis of 26 barium stars, including dwarf barium stars, providing their atmospheric parameters (T_eff, log g, [Fe/H], v_t), and elemental abundances.

Aims.We aim at deriving gravities and luminosity classes of the sample stars, in particular to confirm the existence of dwarf barium stars. Accurate abundances of chemical elements were derived. We present the abundance ratios between nucleosynthetic processes, by using Eu and Ba as representatives of the r- and s-processes.

Methods.High-resolution spectra were obtained with the FEROS spectrograph at the ESO-1.52 m Telescope, along with photometric data with Fotrap at the Zeiss telescope at the LNA. The atmospheric parameters were derived in an iterative way, with temperatures obtained from colour–temperature calibrations. The abundances were derived using spectrum synthesis for Li, Na, Al, α-, iron-peak, s-, and r-element atomic lines, and for C and N molecular lines.

Results.Atmospheric parameters in the range 4300 < T_eff < 6500, -1.2 < [Fe/H] < 0.0, and 1.4 ≤ log g < 4.6 were derived, confirming that our sample contains giants, subgiants, and dwarfs. The abundance results obtained for Li, Al, Na, α-, and iron-peak elements for the sample stars show that they are compatible with the values found in the literature for normal disk stars in the same range of metallicities. Enhancements of C, N, and heavy elements relative to Fe, that characterise barium stars, were derived and showed that [X/Ba] vs. [Ba/H] and [X/Ba] vs. [Fe/H] present different behaviour as compared to [X/Eu] vs. [Eu/H] and [X/Eu] vs. [Fe/H], reflecting the different nucleosynthetic sites for the s- and r-processes.