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

Abstract

Barium stars are optimal sites for studying the correlations between the neutron-capture elements and other species that may be depleted or enhanced, because they act as neutron seeds or poisons during the operation of the s-process. These data are necessary to help constrain the modeling of the neutron-capture paths and explain the s-process abundance curve of the solar system. Chemical abundances for a large number of barium stars with different degrees of s-process excesses, masses, metallicities, and evolutionary states are a crucial step towards this goal. We present abundances of Mn, Cu, Zn, and various light and heavy elements for a sample of barium and normal giant stars, and present correlations between abundances contributed to different degrees by the weak-s, mains, and r-processes of neutron capture, between Fe-peak elements and heavy elements. Data from the literature are also considered in order to better study the abundance pattern of peculiar stars. The stellar spectra were observed with FEROS/ESO. The stellar atmospheric parameters of the eight barium giant stars and six normal giants that we analyzed lie in the range 4300 < T eff /K < 5300, −0.7 < [Fe/H] ≤ 0.12 and 1.5 ≤ log g < 2.9. Carbon and nitrogen abundances were derived by spectral synthesis of the molecular bands of C 2 , CH, and CN. For all other elements we used the atomic lines to perform the spectral synthesis. A very large scatter was found mainly for the Mn abundances when data from the literature were considered. We found that [Zn/Fe] correlates well with the heavy element excesses, its abundance clearly increasing as the heavy element excesses increase, a trend not shown by the [Cu/Fe] and [Mn/Fe] ratios. Also, the ratios involving Mn, Cu, and Zn and heavy elements usually show an increasing trend toward higher metallicities. Our results suggest that a larger fraction of the Zn synthesis than of Cu is owed to massive stars, and that the contribution of the main-s process to the synthesis of both elements is small. We also conclude that Mn is mostly synthesized by SN Ia, and that a non-negligible fraction of the synthesis of Mn, Cu, and Zn is owed to the weak s-process.

Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: a chemo-chronological analysis

“…This may indicate that Mn and Cu do not share the same nucleosynthetic origin. Indeed, Allen & Porto de Mello (2011) found that the synthesis of Cu receives a larger contribution from not so massive stars than Zn, a result roughly in line with those of Castro et al (1999) and ours. Such results point towards the necessity of both more extensive observations of the abundances of Cu and Zn, and more protracted theoretical efforts, in order that a better understanding of the complex chemical history of these two elements may be achieved.…”

“…A decreasing trend in [Zn/Fe] vs. [Fe/H] is seen for stars poorer than the Sun, in agreement with Fig. 1 of Allen & Porto de Mello (2011).…”

“…Even though the statistical significance of the linear regressions is slight, the abundance ratios to Fe of both these elements seem first to increase towards the present epoch, and then decrease (a behaviour that is reinforced when these two elements are plotted together through the mean abundance ratio [Mn, Cu/Fe]). Recalling that Allen & Porto de Mello (2011) have found that Mn is mostly due to SN Ia, our result could imply that the relative yield of Mn to Fe in SN Ia decreases with time (and consequently the overall metallicity). The situation for Cu is less straightforward, as usual.…”

“…The hypothesis of production in SN Ia still stands, but this is probably not the unique source. Allen & Porto de Mello (2011), in their study of s-process enriched stars, suggested that SN Ia is the main source of production of manganese, in opposition to the conclusions of Feltzing et al (2007), who suggested that this element is mainly produced by SN II. Our results in Fig.…”

Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program

“…However, we do not find such a tight correlation with any of the other heavy-s or light-s elements. Later, the work by Allen & Porto de Mello (2011) did not find that Cu-Ba correlation in a sample of barium and normal stars while Zn showed increasing trends with Ba, Sr, Y, Nd, and more tight increasing trends with Eu, and other r-elements (Gd and Dy). Those authors conclude that the r-process is contributing to Zn production with a higher proportion than to Cu for those stars.…”