* Astronomy

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UZ Fornacis

Blobrana · L

Astronomers in South Africa find evidence for a strange new planetary system

Drs. Stephen Potter and Encarni Romero-Colmenero from the South African Astronomical Observatory (SAAO) and collaborators have found evidence for the existence of an extraordinary planetary system where two giant planets are orbiting a close pair of "suns".
If confirmed, this will be an example of a very strange planetary system, given the nature of the stellar pair. The two stars, referred to as a white dwarf and a red dwarf, are each smaller than our Sun and are so close that they take only a couple of hours to orbit each other. The pair of them would actually fit comfortably within our Sun! By chance, the system is oriented in such a way that the stars appear to eclipse each other once every orbit as viewed from Earth. Dr. Potter and his collaborators noticed that the eclipses were not occurring on time, but were sometimes too early or too late. This led them to hypothesise the presence of two giant planets whose gravitational effect would cause the stars' orbit to wobble and consequently slightly alter the measured time between eclipses. The astronomers were also able to infer that the masses of the two planets must be at least 6 and 8 times that of Jupiter and take 16 and 5 years respectively to orbit the two stars. The system is too far away from us to be imaged directly.
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Blobrana · L

Title: Possible detection of two giant extrasolar planets orbiting the eclipsing polar UZ Fornacis
Authors: 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, John Vallerga

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)M(Jupiter) and 7.7(1.2)M(Jupiter)) 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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