20 CVn: Simultaneous uvby photometry

Simultaneous observations in the four uvby filters of the Stromgren photometric system have been collected for the low amplitude delta Sct star 20 CVn and new times of light maxima have been obtained. Some new additional H-beta-Crawford data were also collected. Fourier Transform and classical O-C methods are used to analyse the pulsation of this star. Frequency analysis of our data together with the reanalysis of old photometric data sets suggest this star as a monoperiodic pulsator. From the O-C analysis it seems that the period is decreasing with time. Revision of the different data sets available in the literature does not reveal significant changes in the pulsational amplitude of this star. Intrinsic b-y, m(1) and c(1) values are also derived and the physical parameters are determined. In addition, the analysis of the phase shifts and amplitude ratios between observed light and colour variations suggests that 20 CVn is a radial pulsator in the fundamental mode or first overtone.