Behavior of Li abundances in solar-analog stars: Evidence for line-width dependence

Context. It is known that the surface lithium abundances of field solar-analog G dwarfs show a large dispersion of \ga2 dex (among which our Sun is located at the lower end) despite the similarity of stellar parameters, and planet-host stars tend to show comparatively lower Li abundances in the narrow T_{\rm eff} range. Aims. To investigate the reason for these phenomena, an extensive study of Li abundances and their dependence on stellar parameters was carried out for a homogeneous sample of 118 selected solar analogs based on high-dispersion spectra obtained at Okayama Astrophysical Observatory. Methods. The atmospheric parameters were spectroscopically determined by using the equivalent widths of Fe I and Fe II lines, the ages/masses were estimated from stellar evolutionary tracks, and the width of the macrobroadening (rotation plus macroturbulence) function as well as Li abundances ( A_{\rm Li}) were established by spectrum-fitting analyses. Results. The resulting A_{\rm Li} vs. T_{\rm eff} relation revealed a characteristic inverse-triangle-like distribution enclosed by two clear-cut boundaries (the slanted one running from similar to 5900 K to similar to 5800 K and the vertical one at similar to 5700 K), while the Sun is located around its lowest apex. More significantly, A_{\rm Li} in this region of large dispersion was found to closely correlate with the macrobroadening width (v_{\rm r+m}), which is considered to be the most important parameter. Conclusions. With a reasonable assumption that the difference of rotational velocity is mainly responsible for the variety of v_{\rm r+m}, we may conclude that the stellar angular momentum plays the decisive role in determining the surface Li abundances of solar-analog stars in the T_{\rm eff} range of similar to 5900-5700 K. The low-Li tendency of planet-host stars may thus be interpreted in terms of rotational characteristics.