The radial velocities of the RS CVn star UX Ari ^*,**

A triple system with a binary on the same line of sight

¹ Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
² Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway

Corresponding author: R. Duemmler, Rudolf.Duemmler@Oulu.Fi

Received: 12 October 2000
Accepted: 15 February 2001

Abstract

UX Ari belongs to the class of very active RS CVn stars and has recently been the target of surface (Doppler) imaging. Although this technique needs a quite accurate determination of the orbit (in order to have the correct period for phasing and the correct Doppler shift correction of the line profiles) we found only one, quite old orbit solution, which has subsequently been used by everyone. We used published radial velocities (RVs), supplemented by a large number (124) of our own recent, high-accuracy RVs of both the primary (K0 IV) and the secondary (G5 V) to improve the orbit of UX Ari. In addition to the improved set of parameters, we found that the γ velocity of the system is systematically changing over time. It seems that UX Ari is a triple system. Actually, a third star is weakly present in the spectrum. While its RV is also changing, it is not a member of the system, but happens to be on the same line of sight. Finally, conclusions about the physical parameters of the objects from the orbits are presented.