Behavior of Li abundances in solar-analog stars

Abstract

Context. It is known that the surface lithium abundances of field solar-analog G dwarfs show a large dispersion of >2 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 Teff 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 (ALi) were established by spectrum-fitting analyses. Results. The resulting ALi vs. Teff relation revealed a characteristic inverse-triangle-like distribution enclosed by two clear-cut boundaries (the slanted one running from ∼5900 K to ∼5800 K and the vertical one at ∼5700 K), while the Sun is located around its lowest apex. More significantly, ALi in this region of large dispersion was found to closely correlate with the macrobroadening width (vr+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 vr+m ,w e may conclude that the stellar angular momentum plays the decisive role in determining the surface Li abundances of solar-analog stars in the Teff range of ∼5900–5700 K. The low-Li tendency of planet-host stars may thus be interpreted in terms of rotational characteristics.