9. Looking for explanations
Although the long term energy variations in the visible are rather small compared to the total stellar output (from about 3 to about 1% in decades), one can wonder where this energy variation can be redistributed:
An exclusion between pulsation and "elliptical" (i.e. geometric) variations can explain the decrease of , as non spherical perturbations of the star should damp its radial modes (a limit case being that of Vir, which rotation probably finally got synchronized with its binary orbit). Accordingly, if energy is still available in 16 Lac to feed pulsation, it should appear better in non radial modes ( for example).
A good test of such an explanation would be to monitor carefully the 6.05 d period detected by Jerzykiewicz (eventually a semi-orbital period) and see if there is any correlation between its amplitude and that of and . One should remember here that any such "elliptical" variation would be mixed with the primary's light reflexion onto the secondary (there is about an 8 magnitudes difference between components !).
As pointed out in Paper I, the amplitudes could still be phase-locked with the orbit, the maxima occuring about a fifth of the orbital period after the periastron. At that phase, if the primary is somewhat ellipsoidal, it should also present a maximum apparent surface.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998