Properties and nature of Be stars. 13

A detailed analysis of 149 radial velocities of V923 Aql (HD 183656) from 1927 to 1987 led to the discovery that the object is a spectroscopic binary with an orbital period of 214.75 days and a semiamplitude of 6.2 km s-1. The overlapping long-term radial velocity variations persisted through the whole sixty-year period; the velocity varied from -60 to +20 km s-1 with a quasiperiod of 2120 days (5.8 years) but with large cycle-to-cycle variations in amplitude and cycle length. In particular, the behavior after 1969, when the amplitude was progressively growing, is reminiscent of the onset of a new episode of long-term variability in ζTau. V923 Aql thus becomes the second object (after ζTau), for which the long-term variations could possibly be explained by the revolution of an elongated envelope in the sense predicted by the binary model of the Be phenomenon. (author). 4 figs., 7 tabs., 40 refs