Behavior of Li abundances in solar-analog stars

Y. Takeda, S. Kawanomoto, S. Honda, H. Ando, T. Sakurai
2007 Astronomy and Astrophysics  
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 T 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
more » ... ected 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 Li ) were established by spectrum-fitting analyses. Results. The resulting A Li vs. T eff 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, A Li in this region of large dispersion was found to closely correlate with the macrobroadening width (v 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 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 eff range of ∼5900-5700 K. The low-Li tendency of planet-host stars may thus be interpreted in terms of rotational characteristics. 1 We use the term "efficiency of mixing" as a measure of how Li atoms are effectively conveyed and mixed to the hot inner layer where they are destroyed. Note that two factors may be involved here: the depth of the convection zone (generally deepened with a lowering of T eff ) and the rate of mixing (or shaking efficiency) in the envelope. 2 The possibility of Li deficiency in planet-host stars had been argued by King et al. (1997) and Gonzalez & Laws (2000), which was then criticized by Ryan (2000) as unlikely. However, the arguments in these previous studies are based on insufficient observational data as well as a naive parameterization of A Li (simply in terms of T eff , age/activity, and [Fe/H], referring to open cluster observations), which now appear to be outdated. In contrast, the work of Israelian et al. (2004) is based on a much larger number of planet-host stars, which we may consider more reliable. Article published by EDP Sciences and available at
doi:10.1051/0004-6361:20077220 fatcat:dhs5jstabzec7dq3wqk5gyjaze