Abstract Oscillations of the solar-like star HD 49933 have been thoroughly observed by CoRot. Two dozen frequency shifts, which are closely related to the change in magnetic activity, have been measured. To explore the effects of magnetic activity on frequency shifts, we calculate frequency shifts for the radial and l = 1 p-modes of HD 49933 with the general variational method, which evaluates the shifts using a spatial integral of the product of a kernel and some sources. The theoretical frequency shifts reproduce the observation well. The magnitudes and positions of the sources are determined according to a χ2 criterion. We predict the source that contributes to both the l = 0 and l = 1 modes is located 0.48 − 0.62 Mm below the surface of the star. In addition, based on the assumption that A0 is proportional to the change in the MgII activity index ∆iMgII, we obtain that the change in MgII index between the minimum and maximum of the cycle during the period of HD 49933 is about 0.665. The magnitude of the frequency shifts compared to the Sun already demonstrates that HD 49933 is much more active than the Sun, which is further confirmed in this paper. Furthermore, our calculation of the frequency shifts for l = 1 modes indicates the variation of turbulent velocity in the stellar convective zone may be an important source for the l = 1 shifts.

Keywords stars: individual (HD 49933) — stars: evolution — stars: oscillation — stars: modeling

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