Effect of surface structures on integrated seismology measurements

The presence of a non uniform distribution of large scale structures on stellar surfaces (photospheric temperatures, chromospheric emission, abundances, magnetic fields, intrinsic velocity fields or intrinsic line profile and broadening) induces a rotational modulation of photometric and spectroscopic measurements. In globally integrated flux, profiles or Doppler measurements, this rotational modulation (in amplitude and time curve) has a specific Fourier signature at selected harmonics of the rotation frequency. We calculate the corresponding modulation transfer signature for typical spot and plage parameters in the solar case. We stress the need to estimate and correct such effects from the observed power spectrum in the seismological analysis, especially in the frequency up to the range of gravity modes. Also, due to the oscillation inhibition in magnetic regions, the rotational modulation of the seismological signal, has a specific Fourier signature at the 3 first harmonics of the rotation frequency, appearing as sidelobes around each genuine oscillatory peak that can affect the observed broadening, splitting and line shapes of low frequency p-modes.