CM Draconis
Star in the constellation Draco
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Through Light-year, Parsec and Constellation
According to the system's entry in the Combined General Catalogue of Variable Stars, at least one of the components is a flare star and at least one is a BY Draconis variable. The white dwarf star GJ 630.1B, also known as WD 1633+572, located 25.7 arcseconds away shares the same proper motion as the CM Draconis stars and is thus a true companion star of the system. Given the system's distance of 47 light years, this corresponds to a separation of at least 370 astronomical units between CM Draconis and GJ 630.1B.
History of observations
CM Draconis was discovered to be an eclipsing binary by Olin J. Eggen and Allan Sandage in 1967; at that time it was known by the designation LP 101-15. It was the second M-dwarf eclipsing binary discovered after YY Geminorum (Castor C), and they remained the only two known until CU Cancri (GJ 2069 A) was found to be an eclipsing binary in 1999.
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Search for planets
The system was the subject of a dedicated search for transiting extrasolar planets in orbit around the binary from 1994–1999. In the end, the existence of all of the transiting planet candidates suggested by the project was ruled out.
Based on variations in the timing of the system's eclipses, it has been suggested that there may be an object in a circumbinary orbit around the two red dwarf stars. In 2000, it was proposed that a Jovian planet is orbiting the system with a period of 750–1050 days. A later analysis of timing variations did not confirm this proposed planet and instead suggested that there was a Jovian planet in an 18.5-year orbit, or a more massive object further out. This analysis was itself not supported by a 2009 study that found the eclipse timings were indistinguishable from linear, though the binary stars do have a small eccentricity that may indicate that they are being perturbed by an orbiting body that prevents the orbit from being fully circularised by tidal effects. A massive planet or brown dwarf on an orbit of 50–200 days would fulfil the observational criteria: the requirement for dynamical stability, the constraints from the lack of observed timing variations and the requirement that the object can maintain the eccentricity of the binary stars.
Eclipse timing variations were again discussed by a 2025 study, which found the variations may be caused by either a planet or by intrinsic stellar activity.