Evidence for the detection of a third body orbiting around the eclipsing binary CM Draconis has been obtained using binary stellar eclipse timing method for the first time. Although binary or multiple stars are very frequent in our Galaxy, to date no unambiguously circumbinary planets had been detected.

Artist impression of CM Dra sunset from extrasolar planet (extracted from IAC press release). Credit: Gabriel Pérez (SMM/IAC). [ JPEG ].

CM Dra is a detached spectroscopic eclipsing binary, one of the lowest known total mass. With its nearly edge-on inclination it was chosen as the target of the first photometric search for planetary transits. Performed by the "TEP" project from 1994 to 1999 and over 1000 hours of coverage (see the 1998 review of ING scientific highlights for a summary), no planetary transits were detected. The same data provided, however, a further possibility to detect the presence of third bodies, from their possible light-time effects on the binary's eclipse minimum times.

Using new eclipse minimum timings of CM Dra obtained between the years 2000 and 2007 with the Isaac Newton Telescope among others, and published data going back to 1977, the astronomers were able to detect a variation of a few seconds in the periodicity of the stellar eclipses, which can be attributed to the attraction of a third body.

Two possibilities for the source of CM Dra's timimg variations can be valid: a mass of a few Jupiters on a two decade-long orbit, or an object on a century-to-millenium long orbit, with masses between 1.5 Jupiters and that of a very low mass star.

More information:

• H. J. Deeg, B. Ocaña, V. P. Kozhevnikov, D. Charbonneau, F. T. O'Donovan, L. R. Doyle, 2008, "Extrasolar planet detection by binary stellar eclipse timing: evidence for a third body around CM Draconis", A&A, 480, 563.
• "Alrededor de dos soles", IAC press release, 23rd March, 2008.