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arXiv · 1710.10750

Three new barium dwarfs with WD companions: BD+68 1027, RE J0702+129 and BD+80 670

X. M. Kong·Y. Bharat Kumar·G. Zhao·J. K. Zhao·X. S. Fang·J. R. Shi·L. Wang·J. B. Zhang·H. L. Yan
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Abstract

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, $-$0.06, 0.13) of BD+68$^\circ$1027, RE~J0702+129 and BD+80$^\circ$670 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 (1.47 $M_{\odot}$) and BD+80$^\circ$670 (3.59 $M_{\odot}$), which confirms the predicted range of progenitor AGB masses (1.5 $\sim$ 4 $M_{\odot}$) for unseen WDs around Ba dwarfs. Surface abundances of s-process elements in RE~J0702+129 and BD+80$^\circ$670 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.

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X. M. Kong, Y. Bharat Kumar, G. Zhao, J. K. Zhao, X. S. Fang, J. R. Shi, L. Wang, J. B. Zhang, H. L. Yan. 2017-10-30. Three new barium dwarfs with WD companions: BD+68 1027, RE J0702+129 and BD+80 670. https://doi.org/10.1093/mnras%2Fstx2809

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