Discovery of binarity, spectroscopic frequency analysis, and mode identification of the δSct star 4 CVn?,??

Abstract

More than 40 years of ground-based photometric observations of the δSct star 4 CVn revealed 18 independent oscillation frequencies, including radial as well as non-radial p-modes of low spherical degree ` ≤ 2. From 2008 to 2011, more than 2000 spectra were obtained at the 2.1-m 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 4 CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discovered that 4 CVn is an eccentric binary system, with an orbital period Porb = 124.44 ± 0.03 d and an eccentricity e = 0.311 ± 0.003. We firmly detect 20 oscillation frequencies, 9 of which are previously unseen in photometric data, and attempt mode identification for the two dominant modes, f1 = 7.3764 d−1 and f2 = 5.8496 d−1, and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, veq sin i ' 106.7 km s−1, translates to a rotation rate of veq/vcrit ≥ 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 achiev