Core-valence and core-core correlation effects on hyperfine-structure parameters and oscillator strengths in Tl ii and Tl iii

We report on large-scale ab initio multiconfiguration Dirac-Fock calculations of hyperfine-structure parameters and oscillator strengths for the lowest few levels in Tl II and Tl III. The effect of both core-valence and core-core correlation on these properties is investigated, probing effects of all core subshells. The agreement with most experiments is excellent. These data are of vital interest for the interpretation of recent spectra of the chemically peculiar star {χ} Lupi. {} 1996 The American Physical Society.