The α CrB binary system: A new radial velocity curve, apsidal motion, and the alignment of rotation and orbit axes

¹ Hamburger Sternwarte, Universität Hamburg, 21029 Hambourg, Germany
e-mail: jschmitt@hs.uni-hamburg.de
² Universidad de Guanajuato, Departamento de Astronomía, 36000 Guanajuato, Mexico
³ Institut d’Astrophysique et de Géophysique Université de Liège, 4000 Liège, Belgium

Received: 3 June 2015
Accepted: 12 November 2015

Abstract

We present a new radial velocity curve for the two components of the eclipsing spectroscopic binary α CrB. This binary consists of two main-sequence stars of types A and G in a 17.3599-day orbit, according to the data from our robotic TIGRE facility that is located in Guanajuato, Mexico. We used a high-resolution solar spectrum to determine the radial velocities of the weak secondary component by cross-correlation and wavelength referencing with telluric lines for the strongly rotationally broadened primary lines (v sin(i) = 138 km s^-1) to obtain radial velocities with an accuracy of a few hundred m/s. We combined our new RV data with older measurements, dating back to 1908 in the case of the primary, to search for evidence of apsidal motion. We find an apsidal motion period between 6600 and 10 600 yr. This value is consistent with the available data for both the primary and secondary and is also consistent with the assumption that the system has aligned orbit and rotation axes.