2013ApJ...772L..10T

The determination of pulsation mode and distance for field Cepheids is a complicated problem best resolved by a luminosity estimate. For illustration a technique based on spectroscopic luminosity discrimination is applied to the 4.47 day s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable yield values of < M_V > = -3.40±0.02 s.e. (±0.04 s.d.), average effective temperature T_eff= 6195±24 K, and intrinsic color ( < B > - < V > )₀= +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 are consistent with fundamental mode pulsation for a small-amplitude classical Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A distance of 413±14 pc is estimated from the Cepheid's angular diameter in conjunction with a mean radius of < R > = 39.0±0.7 R_☉ inferred from its luminosity and effective temperature. The dust extinction toward FF Aql is described by a ratio of total-to-selective extinction of R_V= A_V/E(B - V) = 3.16±0.34 according to the star's apparent distance modulus.