On the Radial-Velocity Variation of the Cepheid Variable FF Aquilae

Light-variation.-FF Aquilae is a Cepheid with a period of 4~5 and a visual light- range of o.~mag., the interval from maximum to minimum being I~99, or 0.445 P. Short-period velocity variation-Observations of 1932 and 1933 establish a velocity variation whose curve is a reflection of the, light-curve and whose amplitude is about 14 km/sec. Long~period velocity variation-The mean residuals for the other observing seasons are systematic and seem to be consistent with a change of ~ km/sec. in the systemic velocity in a period of 4109drn Owing to gaps in the observations, the evidence is not C0fl clusive and a definitive answer must be left to the next few years' observations. A maximum departure from the 1932-1933 curve apparently should occur within the next year or two. The corresponding velocity of the system as a whole would be approximate- ly -22 km/sec. Companion star-The Go companion, at least 6.5 mag. fainter than FF Aquilae, must be a dwarf if the two stars form a physical system and if the absolute magnitude of FF Aquilae is to agree with that called for by the period-luminosity law