Behavior of Li abundances in solar-analog stars II. Evidence of the connection with rotation and stellar activity

摘要

We previously attempted to ascertain why the Li I 6708 line-strengths ofSun-like stars differ so significantly despite the superficial similarities ofstellar parameters. We carried out a comprehensive analysis of 118 solaranalogs and reported that a close connection exists between the Li abundanceA_Li and the line-broadening width (v_r+m; mainly contributed by rotationaleffect), which led us to conclude that stellar rotation may be the primarycontrol of the surface Li content. To examine our claim in more detail, westudy whether the degree of stellar activity exhibits a similar correlationwith the Li abundance, which is expected because of the widely believed closeconnection between rotation and activity. We measured the residual flux at theline center of the strong Ca II 8542 line, r_0(8542), known to be a usefulindex of stellar activity, for all sample stars using newly acquired spectra inthis near-IR region. The projected rotational velocity (v_e sin i) wasestimated by subtracting the macroturbulence contribution from v_r+m that wehad already established. A remarkable (positive) correlation was found in theA_Li versus (vs.) r_0(8542) diagram as well as in both the r_0(8542) vs. v_esin i and A_Li vs. v_e sin i diagrams, as had been expected. With theconfirmation of rotation-dependent stellar activity, this clearly shows thatthe surface Li abundances of these solar analogs progressively decrease as therotation rate decreases. Given this observational evidence, we conclude thatthe depletion of surface Li in solar-type stars, probably caused by effectiveenvelope mixing, operates more efficiently as stellar rotation decelerates. Itmay be promising to attribute the low-Li tendency of planet-host G dwarfs totheir different nature in the stellar angular momentum.