Nonradial and radial period changes in the δ Scuti star 4 CVn - I. 700+ nights of photometry

Context. The nature of period and amplitude changes in nonradial pulsators is presently unknown.Aims. It is therefore important to examine the correlations between these changes in stars with a large number of simultaneously excited pulsation modes. However, the small amplitudes require extensive high-precision photometry covering many years.Methods. We present 702 nights of high-precision photometry of the evolved δ Sct variable 4 CVn obtained from 2005–2012 with a dedicated telescope.Results. We detected 64 frequencies, of which 38 can be identified as combinations and harmonics. The relative amplitudes of the combination frequencies are similar to those found in 44 Tau and show no evidence for resonant mode coupling. Significant period and amplitude changes are detected for the dominant modes. The known prograde and retrograde modes show period changes with opposite signs, while the radial mode exhibits only small, cyclical period changes. For each mode, the period changes are constant over the eight years and range from (1 /P )dP / dt = −16 × 10-6 to 13 × 10-6 . On the other hand, the amplitude variations show no systematic behavior between different pulsation modes.Conclusions. The behavior of the prograde, axisymmetric, and retrograde modes indicate a constant decrease in the rotational splitting over the eight years.