2014A&A...570A..33S

More than 40 years of ground-based photometric observations of the δSct star 4CVn has revealed 18 independent oscillation frequencies, including radial as well as non-radial p-modes of low spherical degree l≤2. From 2008 to 2011, more than 2000 spectra were obtained at the 2.1m Otto-Struve telescope at the McDonald Observatory. We present the analysis of the line-profile variations, based on the Fourier-parameter fit method, detected in the absorption lines of 4CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discover that 4CVn is an eccentric binary system with an orbital period P_orb=124.44±0.03d and an eccentricity e=0.311±0.003. We detect 20 oscillation frequencies, 9 of which previously unseen in photometric data; attempt mode identification for the two dominant modes, f₁=7.3764d^–1 and f₂=5.8496d^–1; and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, v_eqsini≃106.7km/s, translates to a rotation rate of v_eq/v_crit≥33%. This relatively high rotation rate hampers unique mode identification, since higher order effects of rotation are not included in the current methodology. We conclude that, in order to achieve unambiguous mode identification for 4CVn, a complete description of rotation and the use of blended lines have to be included in mode-identification techniques.