Turner, David Gerald, 1945-; Kovtyukh, V. V.; Luck, R. E.; Berdnikov, L. N. (IOP Publishing Limited, 2013-07-20)
<p>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<sub>V</sub>> = −3.40 ± 0.02 s.e.
(±0.04 s.d.), average effective temperature T<sub>eff</sub> = 6195 ± 24 K, and intrinsic color (<B>−<V>)<sub>0</sub> =
+0.506±0.007, corresponding to a reddening of
E<sub>B−V</sub> = 0.25 ± 0.01, or E<sub>B−V</sub>
(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<sub>☉</sub> 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<sub>V</sub> = A<sub>V</sub> /E(B − V) = 3.16 ± 0.34 according to the star's apparent distance modulus.</p>...