CM Draconis

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**CM Draconis**
Observation data Epoch J2000.0 (ICRS)
Constellation (pronunciation)	Draco
Right ascension	16^h 34^m 20.321^s^[1]
Declination	+57° 09′ 44.70″^[1]
Apparent magnitude (V)	12.90^[1]
Characteristics
Spectral type	M4.5V, M4.5V
Variable type	Eclipsing binary, Flare star, BY Draconis variable
Astrometry
Radial velocity (R_v)	–118.71^[1] km/s
Proper motion (μ)	RA: –1109^[1] mas/yr Dec.: 1203^[1] mas/yr
Parallax (π)	68 ± 4^[1] mas
Distance	48 ± 3 ly (14.7 ± 0.9 pc)
Absolute magnitude (M_V)	12.1^[2]
Other designations
GJ 630.1, LHS 421, NLTT 43148, G 225-67, USNO-B1.0 1471-00307615, CABS 134, USNO 168, IDS 16326+5721 A

CM Draconis is an eclipsing binary star system consisting of two nearly identical red dwarf stars located in the constellation Draco. The two stars orbit each other with a period of 1.27 days with a separation of 2.7 million kilometres^[3]. 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.^[4] The white dwarf star GJ 630.1B, 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.^[5] Given the system's distance of 48 light years,^[6] this corresponds to a separation of at least 380 astronomical units between CM Draconis and GJ 630.1B.

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.^[7]^[8]

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.^[9] More recent eclipse measurements suggest there may be a planet with a mass similar to Jupiter in an 18.5-year orbit, or instead a more massive object located further out. The variations are inconsistent with being caused by the white dwarf companion star. No further evidence for the 750–1050 day planet was found and it is considered unlikely that it exists.^[5]

[edit] References

^ ^a ^b ^c ^d ^e ^f ^g CM Dra, database entry, SIMBAD. Accessed on line June 2, 2008.
^ From parallax and apparent magnitude.
^ TEP: CM Draconis.
^ Samus (2004). CM Dra. Combined General Catalogue of Variable Stars.
^ ^a ^b Deeg, H. J.; Ocaña, B.; Kozhevnikov, V. P.; Charbonneau, D.; O'Donovan, F. T.; Doyle, L. R. (2008). "Extrasolar planet detection by binary stellar eclipse timing: evidence for a third body around CM Draconis". Astronomy and Astrophysics 480 (2): 563–571.
^ CM Draconis – Variable of BY Dra type. SIMBAD.
^ The TEP network.
^ Doyle, Laurance R.; Deeg, Hans J.; Kozhevnikov, Valerij P.; Oetiker, Brian; Martín, Eduardo L.; Blue, J. Ellen; Rottler, Lee; Stone, Remington P. S.; Ninkov, Zoran; Jenkins, Jon M.; Schneider, Jean; Dunham, Edward W.; Doyle, Moira F.; Paleologou, Efthimious (2000). "Observational Limits on Terrestrial-sized Inner Planets around the CM Draconis System Using the Photometric Transit Method with a Matched-Filter Algorithm". The Astrophysical Journal 535 (1): 338–349.
^ Deeg, H. J.; Doyle, L. R.; Kozhevnikov, V. P.; Blue, J. E.; Martín, E. L.; Schneider, J. (2000). "A search for Jovian-mass planets around CM Draconis using eclipse minima timing.". Astronomy and Astrophysics 358: L5–L8.