Long-term photometric behaviour of XZ Dra Binarity or magnetic cycle of a Blazhko type RRab star

Abstract

The extended photometry available for XZ Dra, a Blazhko type RR Lyrae star, makes it possible to study its long-term behavior. It is shown that its pulsation period exhibit cyclic, but not strictly regular variations with approx. 7200 d period. The Blazhko period (approx. 76 d) seems to follow the observed period changes of the fundamental mode pulsation with dP_B/dP_0=7.7 x 10^4 gradient. Binary model cannot explain this order of period change of the Blazhko modulation, nevertheless it can be brought into agreement with the O-C data of the pulsation. The possibility of occurrence of magnetic cycle is raised.Comment: 13 pages, 11 figures (submitted to A&A