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Astron. Astrophys. 332, 149-154 (1998)

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1. Introduction

UX Arietis is a binary system formed by a spotted K0 IV primary and a G5 V secondary having a 6.44 days orbital period. Vogt and Hatzes (1991) discovered that the spot distribution is rather stable and proved that the spotted star has a differential rotation. Such a rotation, together with the presence of a convection zone, much deeper than that of the Sun, are the necessary ingredients for a very efficient dynamo mechanism, responsible for the high activity of the system (for references see Elias et al. 1995).

An observing campaign dedicated to the UX Arietis binary system has been performed with the 100-m radiotelescope at Effelsberg (Neidhöfer et al. 1993) with the main purpose of obtaining information on possible systematic trends of the stellar activity that may be important for a better understanding of the dynamo process.

In this paper we present the analysis of the data collected during a period of 965 days. In the next section we present the data set observed in the whole period and we determine the possible periodicities of the stellar activity, using two different statistical methods discussed in the Appendix. Light curves are obtained by folding the data with different periods. In Sect. 3 we discuss the light curve obtained by folding the data with the orbital period. In Sect. 4 we present a very good fit to the whole dataset obtained with a suitable periodic function. A possible periodicity in the percentage polarization is considered in Sect. 5. Summary and conclusions are presented in Sect. 6.

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998