The orbit and variations of δ Sagittae

Radial-velocity observations spanning more than a century are used to produce a reliable orbit of the δ Sagittae system. We find an orbital period of 3703.7 ± 1.5 d and a semi-amplitude of 7.73 ± 0.05 km s^-1. In addition, we find quasi-periodic variations with time-scales in the range of 550-750 d and a typical amplitude of 1 km s^-1. The phase and amplitude are both irregular, sometimes changing very abruptly. We consider pulsation, rotational modulation and convection as possible causes of the variations, finally favouring convection.