Three new barium dwarfs with WD companions: BD+681027, RE J0702+129 and BD+80670

We report three new barium (Ba) dwarfs lying in Sirius-like systems, which provides direct evidence that Ba dwarfs are companions to white dwarfs (WDs). Atmospheric parameters, stellar masses, and chemical abundances of 25 elements, including light, α, Fe-peak and s-process elements, are derived from high resolution and high S/N spectra. Enhancement of s-process elements with [s/Fe] ratios between 0.4 and 0.6 confirm them as mild barium stars. The estimated metallicities (−0.31, −0.06, 0.13) of BD+681027, RE J0702+129 and BD+80670 are in the range of known Ba dwarfs and giants. As expected, observed indices of [hs/ls], [s/Fe] and [C/Fe] show anticorrelation with metallicity. AGB progenitor masses are estimated for the WD companions of RE J0702+129 (1.47M⊙) and BD+80 670 (3.59M⊙), which confirms the predicted range of progenitor AGB masses (1.5 ∼ 4 M⊙) for unseen WDs around Ba dwarfs. Surface abundances of s-process elements in RE J0702+129 and BD+80670 are compared with AGB models and they are in close agreement, within predicted accretion efficiencies and pollution factors for Ba stars. These results support that the origin of s-process overabundances in Ba dwarfs is similar to Ba giants via McClure hypothesis in which Ba stars accumulate s-process elements through mass transfer from their host companions during AGB phase.