AAVSO: American Association of Variable Star Observers

Systematic Effects in the Visual Estimation of the Brightness of Red Variable Stars

Volume 48 number 2 (2020)

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Robert R. Cadmus, Jr.
Department of Physics, Grinnell College, Grinnell, IA 50112; cadmus@grinnell.edu


Visual brightness estimates for red variable stars are complicated by a number of effects. These phenomena have been investigated by comparing visual estimates with V-band photometric measurements. The differences between these quantities for individual stars often vary with the V magnitude at the time of the measurement in a way that is different from the collective trend for many stars and corresponds to an underestimate of the full amplitude of variation by visual observers. This may result from biases introduced in the estimation process, specifically in the choice of comparison stars and in the interpolation of the brightness of the variable between them. These results may shed some light on the factors affecting the transformation between visual estimates and photometric V values for red stars and provide some guidance in the use of that transformation. They also provide insight into the visual estimation process itself.