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A spectroscopic analysis was carried out to clarify the properties of KIC11145123 -- the first main-sequence star with a determination ofcore-to-surface rotation -- based on spectra observed with the High DispersionSpectrograph (HDS) of the Subaru telescope. The atmospheric parameters ($T_{\rmeff} = 7600$ K, $\log g = 4.2$, $\xi = 3.1$ km s$^{-1}$ and $ {\rm [Fe/H]} =-0.71$ dex), the radial and rotation velocities, and elemental abundances wereobtained by analysing line strengths and fitting line profiles, which werecalculated with a 1D LTE model atmosphere. The main properties of KIC 11145123are: (1) A low $ {\rm [Fe/H]} = -0.71\pm0.11$ dex and a high radial velocity of$-135.4 \pm 0.2$ km s$^{-1}$. These are remarkable among late-A stars. Our bestasteroseismic models with this low [Fe/H] have slightly high helium abundanceand low masses of 1.4 M$_\odot$. All of these results strongly suggest that KIC11145123 is a Population II blue straggler; (2) The projected rotation velocityconfirms the asteroseismically predicted slow rotation of the star; (3)Comparisons of abundance patterns between KIC 11145123 and Am, Ap, and bluestragglers show that KIC 11145123 is neither an Am star nor an Ap star, but hasabundances consistent with a blue straggler. We conclude that the remarkablylong 100-d rotation period of this star is a consequence of it being a bluestraggler, but both pathways for the formation of blue stragglers -- merger andmass loss in a binary system -- pose difficulties for our understanding of theexceedingly slow rotation. In particular, we show that there is no evidence ofany secondary companion star, and we put stringent limits on the possible massof any such purported companion through the phase modulation (PM) technique.

Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123