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

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2. Periodicities

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).

[FIGURE] Fig. 1. Observations with the Effelsberg 100-m telescope. Dots indicate frequencies higher than 5.4 GHz; open circles frequencies lower than that. The continuous line shows the model fit and crosses show the occurrence of the periodic shadowing (see Sect. 4)

Inspection of Fig. 1 clearly shows that large flares (S [FORMULA] 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.

[FIGURE] Fig. 2. Radio light curves produced by folding the data with the specified periods. The phase interval 0-1 is repeated twice

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.

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998