The ZOO of uvby and Hp light curves of magnetic chemically peculiar stars

Abstract

We present preliminary results of the generalized Principal Component Analysis (PCA) of light curves of 82 magnetic chemically peculiar (further mCP) stars applied to 54 thousand individual photometric observations in the uvby and Hp colours taken from the "On-line database of photometric observations of mCP stars". We show that every of the observed light curves (LCs) can be, with a sufficient accuracy, represented using five parameters of a harmonic polynomial of the second order, and that the third order and higher harmonics reflect only a noise. We found that a prevailing majority of the uvbyHp LCs can be satisfactorily well represented by a linear combination of a constant term and one or two (extraordinarily three) basic, mutually orthonormal functions, which reduces the number of parameters necessarily needed to describe the set of the LCs of a particular star. While the shape of an individual LC depends on the individual distribution of photometric spots on the surface of a rotating star, its amplitude depends on the mechanism of variability. To describe the amplitude of LCs we introduce a robust quantity effective amplitude. Applying the PCA to the set of the effective amplitudes of the LCs in all five colours we revealed at least three different sources of the light variability showing different wavelength dependence. The amplitudes of all the LCs harbor a component monotonously decreasing with increasing wavelengths. The second component reaches a remarkable extremum in the $v$ colour, and is in antiphase relative to the remaining four colours. It occurs particularly at cooler mCP-s having a high degree of the chemical peculiarity. The third component reflects a remarkable diversity of the light curves in the $u$ colour found in a few mCP stars.