Discovery of binarity, spectroscopic frequency analysis, and mode identification of the delta Sct star 4CVn

TL;DR

This study reveals 20 pulsation frequencies and confirms 4CVn as an eccentric binary, providing insights into its oscillation modes and rotational characteristics through extensive spectroscopic analysis.

Contribution

The paper presents the first spectroscopic detection of binary nature and detailed mode identification of 4CVn, including new frequencies not seen in photometry.

Findings

4CVn is an eccentric binary with a 124.44-day orbit.

20 oscillation frequencies detected, 9 new.

High rotation rate complicates mode identification.

Abstract

More than 40 years of ground-based photometric observations of the delta Sct star 4CVn 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 2.1-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 4CVn, which carry clear signatures of the pulsations. From a non-sinusoidal, periodic variation of the radial velocities, we discovered that 4CVn 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 c/d and f2 = 5.8496 c/d, and determine the prograde or retrograde nature of 7 of the modes. The projected rotational velocity of the star, vsini ~ 106.7 km/s, 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 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.