Probing Magnetic Cycles with Photometry of Eclipsing Binaries: XZ Canis Minoris

We present new CCD observations of XZ CMi. A UBVRI light curve analysis and an updated periodicity study are given. Our study shows that the orbital period is decreasing and there is a low amplitude 23-year oscillation in the O-C diagram. Both of these phenomena could be associated with the presence of stellar magnetic activity. XZ CMi is found to be a short-period Algol-type near-contact binary. Our CCD observations were taken 08-12 March 2005 with the Lowell 31-inch reflector and a liquid nitrogen cooled CCD camera with a metachrome coated TEK 512 X 512 chip. Standard UBVR--[c]I[c] filters were used. Some 127 times of minimum light have been determined^2-50. The data show a parabolic trend as well as a low amplitude (0.0051 days, or a light-time of 0.9 AU) oscillation in the quadratic residuals: HJD Tmin I = 24 53441.77225 ± 0.00125 + 0.57880796 ± 0. 00000010*E - 3.5 X 10^ -11 ± 0.3 × 10^-11 d*E^2 + (0.0051 ± 0.0007) Sin[(4.28 × 10^-4 ± 0.1 × 10^-4)*E + 6.2 ± 0.2] We note that 23-year sinusoidal oscillation would be expected from solar-type magnetic cycles. We suggest that high energy observations from spacecraft be undertaken to verify this. A simultaneous BVRI Wilson code solution was obtained revealing that the system is an Algol-type with the secondary, less massive component filling its Roche-lobe and the primary under filling. The third light values varied from 17-18%. The fill-out of the primary component was 92%. Other results are outlined on the poster.

We suggest that precision timings afforded by today's CCD detectors should be analyzed for the effect of magnetic cycles as was done here.