Characterizing the companion AGBs using surface chemical composition of barium stars

Abstract

Barium stars are one of the important probes to understand the origin and evolution of slow neutron-capture process elements in the Galaxy. These are extrinsic stars, where the observed s-process element abundances are believed to have an origin in the now invisible companions that produced these elements at their asymptotic giant branch (AGB) phase of evolution. We have attempted to understand the s-process nucleosynthesis, as well as the physical properties of the companion stars through a detailed comparison of observed elemental abundances of 10 barium stars with the predictions from AGB nucleosynthesis models, FRUITY. For these stars, we have presented estimates of abundances of several elements, C, N, O, Na, Al, α-elements, Fe-peak elements, and neutron-capture elements Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu. The abundance estimates are based on high resolution spectral analysis. Observations of Rb in four of these stars have allowed us to put a limit to the mass of the companion AGB stars. Our analysis clearly shows that the former companions responsible for the surface abundance peculiarities of these stars are low-mass AGB stars. Kinematic analysis has shown the stars to be members of Galactic disc population.

Barium stars as tracers of s-process nucleosynthesis in AGB stars I. 28 stars with independently derived AGB mass

“…We concluded that the metallicity is the best predictor of the sprocess pattern, with lower metallicities favouring the production of the elements of the second peak relative to the first peak, as observed in the Ba stars. This results appear to be confirmed by recent observations of 10 Ba stars (Shejeelammal et al 2020).…”

“…The models have high δ values, but as for CPD −64 • 4333, the short orbital period of the system could explain this phenomenon. Shejeelammal et al (2020) also analysed this star and found an initial AGB mass of 2.5 M ⊙ based on χ 2 minimalisation using FRUITY models. They have found [Fe/H] = −0.5 and generally higher s-process abundances than the data in this study.…”

“…These authors found that AGB models in the mass range from 1.5 M ⊙ to 3.0 M ⊙ and dilution factors from 1 (for dwarf stars) to 30 were required to cover the observed abundances in the sample stars considered. A recent study of Shejeelammal et al (2020) for Ba and CH stars provides abundances for many first and second s-process peak elements, and also including C, Rb and Eu. Comparing the derived abundances to FRUITY nucleosynthesis models these authors confirm that AGB stars with mass 3 M ⊙ are the typical former companions of Ba stars.…”

Rubidium abundances of galactic disk stars

“…These previous studies revealed that the [Rb/Fe] ratio tends to be moderately supersolar (0≲ [Rb/Fe] ≲ 0.5) at the metal‐poor regime ([Fe/H] ≲ −1). Successively, Rb abundances of globular cluster giants (D'Orazi et al 2013; Yong et al 2006, 2008) or AGB giants (García‐Hernández et al 2006; Shejeelammal et al 2020) were also investigated.…”

“…TAKEDA Successively, Rb abundances of globular cluster giants (D'Orazi et al 2013;Yong et al 2006Yong et al , 2008 or AGB giants (García-Hernández et al 2006;Shejeelammal et al 2020) were also investigated.…”