Yellow supergiant reddenings from BVRI data

The use of (B-V) and (R-I) are explored to determine a Cepheid's reddening as well as the reddenings of Cepheid-like stars. The method is essentially the analog in the (B-V), (R-I)-plane of the Q-method introduced by Johnson and Morgan (1953) for the UBV system. An expression is shown to reproduce the color excesses given by Parsons and Bell (1975) for stable F and G supergiants with an rms deviation of less than 0.03 mag. The same expression is applicable to classical Cepheids at mean light, but if it is applied to Cepheid observations at some particular phase, a correction taking into account the amplitude of the Cepheid's visual lightcurve must be added. For Cepheids at mean light the rms deviation of the present results from those of Parsons and Bell is again 0.03 mag, rising to 0.04 mag when observations at individual phases are used. Color excesses so determined are listed for 41 Cepheids and 17 stable supergiants.