UX Arietis has been observed with the Effelsberg 100-m telescope over a frequency range spanning from 1.4 GHz (21 cm) to 43 GHz (7 mm) collecting a total number of 269 samples over a period of 965 days. The set of data obtained is presented in Fig. 1 as a function of the Julian Day. The data are plotted together with their error bar. For detail on the observations we refer to Neidhöfer et al. (1993).
Inspection of Fig. 1 clearly shows that large flares (S mJy) are only observed at high frequencies. In order to check whether the activity shown in Fig. 1 presents any periodicity, we have analyzed the whole data set using two independent methods of period determination together with a simulation procedure. This data processing, described in detail in the Appendix, has given as a result a dominant period at 25.5 days and two other periods at 14.4 and 158.7 days. A further check of the spectral analysis is supplied by the plots of the data as a function of phase for each determined period. The data folded with a given period will cluster around a specific phase when the periodicity is real, while, if there is no periodicity, they will appear uniformly scattered at all phases.
The data, plotted in Fig. 2, indicate a clear periodicity, shown by the considerable cluster around phase 0.8, when folded with the 14.4 days period and around phase 0.1 when folded with the 25.5 days period.
The data folded with the long term period of 158.7 days appear to cluster in a different way: they recall a square wave rather than a sinusoidal trend as in the two preceeding plots. In this step function the upper level lasts longer (0.5-1.1) than the lower one.
© European Southern Observatory (ESO) 1998
Online publication: March 10, 1998