V388 Cygni - A binary system in the rapid phase of mass exchange

Using the Wilson & Devinney approach, we analyse the only existing, as far as we know, photoelectric lightcurve of V388 Cyg ( P = 0.859 day, Sp = A3). The absence of any spectroscopic indication of the mass ratio was overcome by the computation of a grid of solutions with many values of q = .LcUh which fixed a well-determined range of possible q 's. Por every possible value of q, the primary (more massive and hotter) component fills its lobe, while the secondary, although detached, is not far from contact. It is suggested that V388 Cyg is a semi-detached system in the rapid phase of case A mass exchange, like SZ Psc and BF Aur. This possibili ty is discussed, taking into account the observed period variations as well. Although only spectroscopic information may salve the problem of the evolutionary stage of V388 Cyg, we find that the inferred configuration is at least very probable and that no evidence exists against it.