Calculation of isotope shifts and King-plot nonlinearities in Ca⁺

Many-body perturbation theory is implemented to calculate the isotope shifts of 4s, 4p(1/)2, 4p(3/2), 3d(3/2), and 3d(5/2) energy levels of Ca+ for even isotopes A = 40, 42, 44, 46, 48. The results are presented for mass shift and field shift, as well as for higher-order field shifts, quadratic mass shift, nuclear polarization correction, and the cross term between field and mass shifts. Additionally, we examine King-plot nonlinearities introduced by higher-order isotope-shift corrections to the combinations of 3d(3/2) -> 4s, 3d(5/2) -> 4s, and 4p(1/2) -> 4s transitions. For these transitions, second-order mass shift and nuclear polarization correction are identified as the dominant sources of King-plot nonlinearity.