| Observation data EpochJ2000.0 EquinoxJ2000.0 (ICRS) | |
|---|---|
| Constellation | Draco |
| Right ascension | 16h 34m 20.33027s[2] |
| Declination | +57° 09′ 44.3689″[2] |
| Apparent magnitude (V) | 12.87[3] |
| Characteristics | |
| Spectral type | M4.5V / M4.5V[4] / DQ8[5] |
| Variable type | BY Draconis variable Eclipsing binary Flare star |
| Astrometry | |
| Radial velocity (Rv) | –118.24[3] km/s |
| Proper motion (μ) | RA: –1113.797mas/yr[2] Dec.: 1180.977mas/yr[2] |
| Parallax (π) | 67.2876±0.0337 mas[2] |
| Distance | 48.47 ± 0.02 ly (14.862 ± 0.007 pc) |
| Absolute magnitude (MV) | 12.1[citation needed] |
| Orbit[6] | |
| Period (P) | 1.268390011(3) d |
| Semi-major axis (a) | 3.6712±0.0053 R☉ |
| Eccentricity (e) | 0.0038±0.0031 |
| Inclination (i) | 89.96±0.06° |
| Longitude of the node (Ω) | 15.79[4]° |
| Argument of periastron (ω) (secondary) | 119±3° |
| Semi-amplitude (K1) (primary) | 72.23[4] km/s |
| Semi-amplitude (K2) (secondary) | 77.95[4] km/s |
| Details[6] | |
| Aa | |
| Mass | 0.2307±0.0008 M☉ |
| Radius | 0.2638±0.0011 R☉ |
| Luminosity | 0.0060±0.0005 L☉ |
| Surface gravity (log g) | 4.959±0.006 cgs |
| Temperature | 3130 ± 70[4] K |
| Metallicity[Fe/H] | −0.30±0.12[7] dex |
| Age | 4.1 ± 0.8[4] Gyr |
| Ab | |
| Mass | 0.2136±0.0008 M☉ |
| Radius | 0.2458±0.0010 R☉ |
| Luminosity (bolometric) | 0.0050±0.0004 L☉ |
| Surface gravity (log g) | 4.959±0.006 cgs |
| Temperature | 3120 ± 70[4] K |
| Metallicity[Fe/H] | −0.30±0.12[7] dex |
| Age | 4.1 ± 0.8[4] Gyr |
| B | |
| Mass | 0.58[5] M☉ |
| Temperature | 6126[5] K |
| Other designations | |
| Eclipsing binary:CM Dra,GJ 630.1A,CCDM J16343+5710A,WDS J16345+5709A,LHS 421,LP 101-15,NLTT 43148,TIC 199574208[3] | |
| White dwarf:GJ 630.1B,CCDM J16343+5710B,WDS J16345+5709B,EGGR 258,LHS 422,LP 101-16,NLTT 43149,WD 1633+572,TIC 199574211[5] | |
| Database references | |
| SIMBAD | A |
| B | |
| ARICNS | A |
| B | |
CM Draconis (GJ 630.1A) is aneclipsing binary star system 48.5light-years (14.9parsecs) away in theconstellation ofDraco (theDragon). The system consists of two nearly identicalred dwarf stars that orbit each other with a period of 1.268days and a separation of 2.6 million kilometres (0.017 AU).[8] Along with two stars in the triple systemKOI-126, the stars in CM Draconis are among the lightest stars with precisely measured masses and radii. Consequently, the system plays an important role in testing stellar structure models for very low mass stars.[4] These comparisons find that models underpredict the stellar radii by approximately 5%. This is attributed to consequences of the stars' strong magnetic activity.[4]
According to the system's entry in theCombined General Catalogue of Variable Stars, at least one of the components is aflare star and at least one is aBY Draconis variable.[9] Thewhite dwarf starGJ 630.1B, also known asWD 1633+572, located 25.7arcseconds away shares the sameproper motion as the CM Draconis stars and is thus a true companion star of the system.[10] Given the system's distance of 47light years,[11] this corresponds to a separation of at least 370astronomical units between CM Draconis and GJ 630.1B.
CM Draconis was discovered to be an eclipsing binary byOlin J. Eggen andAllan Sandage in 1967; at that time it was known by the designation LP 101-15.[12] It was the second M-dwarf eclipsing binary discovered after YY Geminorum (Castor C),[13] and they remained the only two known until CU Cancri (GJ 2069 A) was found to be an eclipsing binary in 1999.[14]
The system was the subject of a dedicated search for transitingextrasolar 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.[15][16]
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.[17] 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.[10] 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 orbrown 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.[4]
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.[6]
