High-Dispersion Spectroscopic Study of Solar Twins: HIP 56948, HIP 79672, and HIP 100963

An intensive spectroscopic study was performed for three representative solar twins (HIP 56948, HIP 79672, and HIP 100963) as well as for the Sun (Moon; reference standard), with intentions of (1) quantitatively discussing the relative-to-Sun similarities based on the precisely established differential parameters and (2) investigating the reason that causes the Li abundance differences, despite their similarities. It was concluded that HIP 56948 most resembles the Sun in every respect, including the Li abundance (though not perfectly similar) among the three, and deserves the name of closest-ever solar twin, while HIP 79672 and HIP 100963 have a somewhat higher effective temperature and appreciably higher surface Li composition. While there is an indication of Li being rotation-dependent, because the projected rotation in HIP 56948 (and the Sun) is slightly lower than the other two, the rotational difference alone does not seem to be so large as to efficiently produce a marked change in Li. Rather, this may be more likely to be attributed (at least partly) to a slight difference in T-eff via some T-eff-sensitive Li-controlling mechanism. Since the abundance of Be was found to be essentially solar for all stars irrespective of Li, any physical process causing the Li diversity should work only on Li without affecting Be.