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The pulsation mode and distance of the Cepheid FF Aquilae
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Abstract:
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 <MV> = −3.40 ± 0.02 s.e. (±0.04 s.d.), average effective temperature Teff = 6195 ± 24 K, and intrinsic color (<B>−<V>)0 = +0.506±0.007, corresponding to a reddening of EB−V = 0.25 ± 0.01, or EB−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 RV = AV /E(B − V) = 3.16 ± 0.34 according to the star's apparent distance modulus.
Description:
Subject:
- Cepheids
- Variable stars
