Observational studies of 12 DD Lacertae. II

Analysis of the radial velocity curves of 12 DD Lacertae shows that the primary period is decreasing and the secondary is almost constant, confirming the photometric results previously reported. Wesselink's method applied to the simultaneous light and radial velocity observations can reveal physical properties that are comparable with the present situation if the temperature variation is assumed to be about 2000 K, as well as when applied to the combined normal curves of the primary period, except at the maximum contraction corresponding to the phase of line broadening which must be the splitting of the line into two components at a higher dispersion. It must be mentioned however, that the normal variation of the higher modes was nothing but tentative description. It is also shown that the behaviour of variation of absorption line profiles with radial velocity is similar to that of γ Eridani and BW Vulpeculae, on which the analyses were already reported, disclosing a sudden sharpening in the middle of the line broadening phase although it seems to be a much more complicated or unstable phenomena probably owing to the effect of multiperiodicity. (Auth.)