2. Basic data

The AAVSO has compiled observed times and visual magnitudes for maxima and minima of about 400 LPVs since 1900 (Mattei 1988). Our study is performed on these data which were also used in the preparation of the HIPPARCOS mission. Some stars were excluded from the sample either because of the peculiar shape of their light curves (e.g, double maxima: R Cen, R Nor, RZ Cyg, etc.), or due to insufficient data. The final sample contains 355 stars.

For each star the following parameters of the light curve were derived:

• Period, P: time (in days) from one maximum to the following one.
• Amplitude, A: magnitude difference between the maximum and the minimum.
• Asymmetry factor, f: the ratio of the increasing time (from minimum to the following maximum) to the period.
• Magnitude, Max, at maximum brightness.
• Magnitude, min, at minimum brightness.
• Their respective standard deviations: , , , , .