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Astron. Astrophys. 342, 709-716 (1999)

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6. Conclusions

We confirm the variability of the radio flux density of the Algol-type binary system RZ Cas, that cannot be ascribed to any geometrical effects related to an eclipse of the radio source. Instead, the observed variability and the changes in the radio spectrum are consistent with a core-halo morphology of the radio emitting corona, where the physical conditions vary due to the magnetic activity.

The existence of such a structured corona is supported by almost simultaneous X-ray observations, reported in the literature, and carried out with ROSAT. The X-ray flux is, in fact, well reproduced by assuming two distinct regions of the corona, characterized by different temperature and emission measures. When physical parameters, as derived from radio spectra, are combined with those inferred from X-ray observations, a co-spatial model for the X-ray and radio source can be outlined, where the radio structures, i.e. core and halo, correspond to the two X-ray emitting regions. Finally, the quiescent radio emission of RZ Cas cannot be attributed to gyrosynchrotron from a thermal population of emitting particles, as already pointed out in a recent paper by Umana et al. (1998). Therefore, the observed quiescent flux density requires a presence of energetic nonthermal electrons in the corona, even in epochs of low level of magnetic activity. By variability timescale considerations we have shown that these energetic electrons must be supplied almost continuously, in order to maintain the observed quiescent radio component.

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999
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