4. Application of the correction function
To test the procedure and verify the resulting mean magnitudes, several BVRI data sets of Cepheids were taken from Wisniewski & Johnson (1968 ) and Freedman et al. (1992 ) as well as BVI light curves for LMC Cepheids from Walker (1987 ). The mean magnitudes obtained with our procedure compare very well with those derived from digitizing the smooth curves, converting into intensities, integrating and then converting back to an intensity-averaged magnitude. For three to four isolated measurements per star and a sample of ten different Cepheids the magnitude residuals are = 0.02 0.06 (sd), = 0.00 0.06 (sd) and = 0.00 0.05 (sd). The quality of the final mean magnitude depends strongly on the number of isolated measurements and the actual phase coverage. At optical passbands a minimum of four observations is needed to provide a meaningful check of the consistency of the solution, in the infrared three phase points are sufficient because of the smaller amplitude.
Our relations were derived from observations in the Johnson R and I passbands, whereas modern photometric observations are made in the Cousins system. However, this difference is negligible for the present purpose.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998