1999A&A...349..225B

The evolved δ Scuti variable 4 CVn was observed photometrically for 53 nights on three continents. We found a total of 34 significant and 1 probable simultaneously excited frequencies. Of these, 16 can be identified as linear combinations of other frequencies. All significant frequencies outside the 4.5 to 10c/d (52 to 116µHz) range can be identified with frequency combinations, f_i±f_j, of other modes with generally high amplitudes. There exists a number of closely spaced frequencies with separations of ∼0.06c/d. This cannot be explained in terms of amplitude variability. The results show that even for stars on and above the main sequence other than the Sun, a very large number of simultaneously excited nonradial oscillations can be detected by conventional means. Since all pulsation modes with photometric amplitudes of 1mmag or larger have now been detected for this star, a presently unknown mode selection mechanism must exist to select between the 1000+ of low-degree modes predicted to be excited for this (and many other) stars. Phase differences and amplitude ratios between the y and v colors are determined for the ten main modes. The phase differences indicate p₁ to p₄ modes of l = 1 for four of these modes. The formulae to determine the uncertainties in the amplitudes and phases of sinusoidal fits to observational data are derived in the Appendix.