Possible detection of two giant extrasolar planets orbiting the eclipsing polar UZ Fornacis

Stephen B. Potter, Encarni Romero–Colmenero, Gavin Ramsay, Steven Crawford, Amanda Gulbis, Sudhanshu Barway, Ewald Zietsman, Marissa Kotze, David A. H. Buckley, Darragh O’Donoghue, O. H. W. Siegmund, J. McPhate, B. Y. Welsh and John Vallerga


Fig. 1. A sample of our new eclipse observations phased on our new ephemeris (section 4.2) Vertical grey bars indicate ingress and egress of the main accretion spot. Solid vertical bars indicate times of white dwarf ingress and egress assuming a duration of 40s.

ABSTRACT

We present new high-speed, multi-observatory, multi-instrument photometry of the eclipsing polar UZ For in order to measure precise mid-eclipse times with the aim of detecting any orbital period variations. When combined with published eclipse times and archival data spanning ∼27 years, we detect departures from a linear and quadratic trend of ∼60 s. The departures are strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The two favoured mechanisms to drive the periodicities are either two giant extrasolar planets as companions to the binary (with minimum masses of 6.3(1.5)MJup and 7.7(1.2)MJup) or a magnetic cycle mechanism (e.g. Applegate’s mechanism) of the secondary star. Applegate’s mechanism would require the entire radiant energy output of the secondary and would therefore seem to be the least likely of the two, barring any further refinements in the effect of magnetic fields (e.g. those of Lanza et al.). The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable. It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.

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Last Revised: 2011 June 8th