MCHF calculations of isotope shifts and oscillator strengths for transitions between low-lying states in Be-like systems and neutral magnesium

Results from systematic multiconfiguration Hartree-Fock calculations of iso tope shifts and oscillator strengths are reported for the 2s(2) - 2s2p and 2s2p - 2p(2) transitions in the Be isoelectronic sequence (Z = 4-10). In ad dition values for the same properties as well as for the hyperfine interact ion constants are presented for the 3s(2)-3s3p transitions in Mg I. Differe nt models for electron correlation are used, and it is shown that valence a nd core-valence effects alone are not sufficient to obtain accurate values for the isotope shifts, but that also core-core effects need to be accounte d for.