Calibration of the Barnes-Evans Relation Using Interferometric Observations of Cepheids

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Abstract
Direct diameter observations of Cepheid variables are used to calibrate the Barnes-Evans Cepheid surface brightness relation. Fifty-nine separate Cepheid diameter measurements from four different optical interferometers are used to calculate surface brightnesses as a function of magnitude and color. The linear fit to Cepheid surface brightness versus color is in excellent agreement with functions in the literature found using interferometric observations of nonvariable giant and supergiant stars. Using these relations, the distance is calculated to δ Cephei, for which an independent distance is known from trigonometric parallax. The distance from the relation in this paper differs from that derived by the previously published relation by 4% but is still marginally within the combined errors. Both distances are well within the errors of the distance derived from trigonometric parallax.
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