SIMBAD references

The nature of the relationship between visual brightness estimates for red stars and the corresponding V magnitudes has been investigated by comparing visual estimates in the American Association of Variable Star Observers database to photoelectric photometry of 39 semiregular variable stars obtained at Grinnell College over a 30 yr period. A general mathematical description of this relationship has been developed, but it applies only approximately for many individual stars because the actual relationship can be quite different for different stars. The overall trends should apply to visual magnitude estimates for red stars generally. These results are based on far more data over a wider range of color than was the case in earlier work and should provide a more robust description of the relationship between photometric measurements and visual estimates. A number of other issues related to visual magnitude estimates are also addressed.