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The determination of pulsation mode and distance for field Cepheids is acomplicated problem best resolved by a luminosity estimate. For illustration atechnique based on spectroscopic luminosity discrimination is applied to the4.47d s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variableyield values of <Mv>=-3.40+-0.02 s.e.(+-0.04 s.d.), average effectivetemperature Teff=6195+-24 K, and intrinsic color (<B>-<V>)o = +0.506+-0.007,corresponding to a reddening of E(B-V)=0.25+-0.01, or E(B-V)(B0)=0.26+-0.01.The skewed light curve, intrinsic color, and luminosity of FF Aql areconsistent with fundamental mode pulsation for a small amplitude classicalCepheid on the blue side of the instability strip, not a sinusoidal pulsator. Adistance of 413+-14 pc is estimated from the Cepheid's angular diameter inconjunction with a mean radius of <R>=39.0+-0.7 Rsun inferred from itsluminosity and effective temperature. The dust extinction towards FF Aql isdescribed by a ratio of total-to-selective extinction ofRv=Av/E(B-V)=3.16+-0.34 according to the star's apparent distance modulus.

The Pulsation Mode and Distance of the Cepheid FF Aquilae