tokens: [Ba/Fe]=+0.13 that is significantly above the pristine [Ba/Fe] dex enrichment in Fig. 6 . This suggests that HD 26749 should have a degenerate companion and should have experienced a former epoch of wind accretion. The observable depletion of lithium qualitatively supports this scenario, but for a quantitative argument one would at least need to know the exact amount of the accreted mass. In this context, it is interesting to note that HD 26749 is currently in its subgiant stage of evolution and appears to be 1 or 2 Gyr younger than one might expect for an ancient Population II star. The excess of mass involved amounts to a few hundredths of a solar mass, a reasonable value for wind accretion, but this also depends on a parallax that would need to account for potential orbital motion. While this parallax may be possible with the Gaia DR3 release, it may be worthwhile to observe HD 26749 with high-contrast direct imaging that may disclose the degenerate candidate companion. 4.1.10 HD 34297 Two Hipparcos -based astrometric orbits by Goldin Makarov ( 2006 ) provide an orbital period of about 2 yr for this double-lined spectroscopic binary. The quantitative composite modelling of our Δ v r (Aa–Ab) =+28.9 km s −1 well-resolved 2017 November 28 spectrum of HD 34297 leads to a photometric contrast Δ m V ≃ 0.5 mag, a Population II chemistry [Fe/H]≃ −0.65 and [Fe/Mg]≃ −0.37, and effective temperatures T eff, Aa ≃ 5660 K and T eff, Ab ≃ 5440 K. The surface gravities, log g Aa ≃ 4.43 and log g Ab ≃ 4.53, follow from the Gaia DR2 parallax. Fig. 1 gives an example of the synthetic line formation for the Fe I line λ6200.321. With reference to the bolometric magnitudes M bol, Aa ≃ 4.96 and M bol, Ab ≃ 5.43 and VandenBerg et al. ( 2006 ) evolutionary tracks, the Aa primary, with a stellar radius R Aa ≃ 0.92 R ⊙ and mass M Aa ≃ 0.82 M ⊙ , is already approaching its turnoff position. The Ab secondary is still close to the main sequence at R Ab ≃ 0.80 R ⊙ and M Ab ≃ 0.79 M ⊙ . Our single-epoch radial velocities, and km s −1 , then provide a systemic velocity γ = +27.64 ± 0.27 km s −1 . 4.1.11 HD 51929 This is a known astrometric and spectroscopic binary (Wielen et al. 1999 ; Nordström et al. 2004 ; Makarov Kaplan 2005 ; Frankowski et al. 2007 ); our single-epoch radial velocity, km s −1 (2017 November 28), deviates by 3.73 km s −1 from the Nordström et al. ( 2004 ) velocity. The Ab companion was recently uncovered through direct imaging at ρ = 0.72 arcsec by Kane et al. ( 2019 ), who assess this to be a faint red dwarf, which we do confirm, since the Aa primary displays the pristine [Ba/Fe] dex enrichment (cf. Table 3 and Fig. 6 below). 4.1.12 HD 65721 For this astrometric and spectroscopic binary (Wielen et al. 1999 ; Nordström et al. 2004 ), Hipparcos -based orbital solutions were first presented in Goldin Makarov ( 2006 , 2007 ). In spite of their preliminary character with d and , the eccentricity appears indeed high, for HD 65721 presents an
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