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Behavior of Li abundances in solar-analog stars. Evidence for line-width dependence
Context: It is known that the surface lithium abundances of fieldsolar-analog G dwarfs show a large dispersion of ⪆2 dex (among whichour Sun is located at the lower end) despite the similarity of stellarparameters, and planet-host stars tend to show comparatively lower Liabundances in the narrow T_eff range. Aims: To investigate thereason for these phenomena, an extensive study of Li abundances andtheir dependence on stellar parameters was carried out for a homogeneoussample of 118 selected solar analogs based on high-dispersion spectraobtained at Okayama Astrophysical Observatory. Methods: Theatmospheric parameters were spectroscopically determined by using theequivalent widths of Fe i and Fe ii lines, the ages/masses wereestimated from stellar evolutionary tracks, and the width of themacrobroadening (rotation plus macroturbulence) function as well as Liabundances (A_Li) were established by spectrum-fitting analyses.Results: The resulting A_Li vs. T_eff relation revealed a characteristicinverse-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. Moresignificantly, A_Li in this region of large dispersion was found toclosely correlate with the macrobroadening width (v_r+m), which isconsidered to be the most important parameter. Conclusions: With areasonable assumption that the difference of rotational velocity ismainly responsible for the variety of v_r+m, we may conclude that thestellar angular momentum plays the decisive role in determining thesurface Li abundances of solar-analog stars in the T_eff range of~5900-5700 K. The low-Li tendency of planet-host stars may thus beinterpreted in terms of rotational characteristics.Based on observations carried out at Okayama Astrophysical Observatory(Okayama, Japan). Tables 2-6 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/468/663
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