Oscillation spectra of line depth, intensity and velocity from radiative transfer calculations

Theoretical spectra for solar oscillations, as they are observed by the MDI instrument, have been calculated by modifying a model of the solar interior according to the oscillations of temperature, pressure, density, and velocity, and calculating the detailed radiative transfer for the Ni I absorption line at 6768 Å with the radiative transfer code COSI. Using the filter functions from the MDI instrument, MDI velocity, intensity, and line depth spectra are modelled. We investigate the intrinsic mode peak asymmetry of velocity, continuum intensity, and line depth spectra. We compare this to the recent results of Georgobiani et al. (2003) who found positive asymmetry for resonance peaks of high-l modes in intensity. Furthermore, we look at the mutual phases of the different quantities, and we show that the decay in power with increasing frequency is most pronounced in velocity and least pronounced in line depth spectra. This is a possible explanation for the high pseudo-mode visibility in line depth spectra.