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A new large sample of 895 s-process-rich candidates out of 454180 giant starssurveyed by LAMOST at low spectral resolution (R ~ 1800) has been reported byNorfolk et al. (2019; hereafter N19). We aim at confirming the s-processenrichment at the higher resolution (R ~ 86000) offered by the HERMES-Mercatorspectrograph, for the 15 brightest targets of the previous study sample whichconsists in 13 Sr-only stars and two Ba-only stars. Abundances were derived forelements Li, C, N, O, Na, Mg, Fe, Rb, Sr, Y, Zr, Nb, Ba, La, and Ce. Binarityhas been tested by comparing the Gaia DR2 radial velocity with the HERMESvelocity obtained 1600 - 1800 days later. Among the 15 programme stars, fourshow no s-process overabundances ([X/Fe] < 0.2 dex), eight show mild s-processoverabundances (at least three heavy elements with 0.2 < [X/Fe] < 0.8), andthree have strong overabundances (at least three heavy elements with [X/Fe] >0.8). Among the 13 stars classified as Sr-only by the previous investigation,four have no s-process overabundances, eight are mild barium stars, and one isa strong barium star. The two Ba-only stars turn out to be both strong bariumstars and are actually dwarf barium stars. They also show clear evidence forbeing binaries. Among the no-s stars, there are two binaries out of four,whereas only one out of the eight mild barium stars show a clear signature ofradial-velocity variations. Blending effects and saturated lines have to beconsidered very carefully when using machine-learning techniques, especially onlow-resolution spectra. Among the Sr-only stars from the previous study sample,one may expect about 60% (8/13) of them to be true mild barium stars and about8% to be strong barium stars, and this fraction is likely close to 100% for theprevious study Ba-only stars (2/2).

astronomy and astrophysics

Sr and Ba abundance determinations: comparing machine-learning with  star-by-star analyses -- High-resolution re-analysis of suspected LAMOST  barium stars