The veiling spectrum of DI Cephei and its relationship to emission line profiles

High spectral resolution variability studies of classical T Tauri stars (CTTS) are an essential instrument for probing the physical conditions and dynamics of their atmospheres and immediate vicinity. The shapes of the excess continuum emission and of the line profiles, their variability and relationship are all crucial tools to achieve that goal. We use high spectral resolution optical data of the CTTS DI Cep to suggest a new diagnostic tool to investigate the relationship between the line emission/absorption and the excess continuum emission. By correlating the veiling continuum to the line flux in discrete velocity bins across the emission line we obtain a correlation profile, from which one can discriminate between parts of the line that relate differently to the veiling. An earlier report of an unexpected hump around 5300 Å in the continuum excess emission spectrum of a couple of CTTS is not explained by current models of those stars. We identified a similar feature in the veiling spectrum of DI Cep and discuss, in this context, the relevance of the broad photospheric absorption features present in the spectra of late-type stars. Regarding DI Cep, we find that its radial velocity seems to be variable but no significant periodicity could be derived, possibly due to inadequate time sampling. We argue that this CTTS is most probably observed nearly equator on. Accretion flows could not be identified directly in the emission lines, but their presence is inferred from the analysis of the veiling spectrum, which yields typical projected accretion rates around $2.5\times10^{-7}$ $M_\odot$ yr-1.