Monday, 23 January 2012

Giant planet in the RR Caeli System.

RR Caeli is an eclipsing binary star system in the constellation of Caelum, 36 light years from Earth. The name implies the tenth variable star in the constellation of Caelum, but the variability is in fact the two stars passing in front of one-another in our line of sight (eclipsing), rather than any variation in their output. The system is referred to as a pre-cataclysmic binary, as the two stars are thought to be in a decaying orbit, that will eventually cause them to collide, but this will not happen for 9-20 billion years, so we are unlikely to be around to see it (our own sun will probably swell into a Red Giant and swallow the Earth in about 5.4 billion years, so the 'pre-cataclysmic' RR Caeli system should be safe for longer than our own solar system).

The position of RR Caeli (RR Cae). The position of East (bottom right)is reversed as this is a map of the sky. The scale bar is 5 arc-minutes; the sky is divided into 360 degrees (assuming the Earth is invisible and you can see underneath you) and each degree into 60 arc-minutes. From Bruch and Diaz (1998).

The two stars of the RR Caeli system are a cool White Dwarf star 44% of the mass of the Sun and a smaller M4-type Red Dwarf with 18.2% of the Sun's mass. These two orbit about one-another every 7.3 hours.

On 2 January 2012 a team lead by S.B. Qian of the Yunnan Observatory and the Chinese Academy of Sciences published a paper on arXiv online database at Cornell University Library, detailing the discovery a planet in the RR Caeli system, using data collected by the Jorge Sahade Telescope at the Complejo Astronómico El Leoncito in San Juan, Argentina.

Qian et al. were able to detect minute variations in the period of RR Caili, from which they were able to infer the presence of a planet with a mass of 4.2 times that of Jupiter, orbiting RR Caeli at a distance of 5.3 AU (5.3 times the distance between the Earth and the Sun, or 2% more than the distance at which Jupiter orbits the Sun) every 11.9 years, with an apparent eccentricity of zero (i.e. in a completely circular path, rather than an elliptical one like most planets). The orbital period of 11.9 years is so close to the orbital period of Jupiter (11.86 years) that the team were concerned that the gravitation influence of Jupiter might be somehow influencing their findings, however they were eventually able to rule this out.

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