# CM Draconis

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Star in the constellation Draco

CM Draconis A red band light curve for CM Draconis, adapted from Kozhevnikova et al. (2009)[1] Observation data Epoch J2000.0 Equinox J2000.0 (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: –1113.797 mas/yr[2] Dec.: 1180.977 mas/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 an [eclipsing binary](/source/Eclipsing_binary) star system 48.5 [light-years](/source/Light-year) (14.9 [parsecs](/source/Parsec)) away in the [constellation](/source/Constellation) of [Draco](/source/Draco_(constellation)) (the [Dragon](/source/Dragon)). The system consists of two nearly identical [red dwarf](/source/Red_dwarf) stars that orbit each other with a period of 1.268 [days](/source/Day) and a separation of 2.6 million kilometres (0.017 AU).[8] Along with two stars in the triple system [KOI-126](/source/Kepler_Object_of_Interest#Non-planet_discoveries), 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 the [Combined General Catalogue of Variable Stars](/source/General_Catalogue_of_Variable_Stars), at least one of the components is a [flare star](/source/Flare_star) and at least one is a [BY Draconis variable](/source/BY_Draconis_variable).[9] The [white dwarf](/source/White_dwarf) star **GJ 630.1B**, also known as **WD 1633+572**, located 25.7 [arcseconds](/source/Arcsecond) away shares the same [proper motion](/source/Proper_motion) as the CM Draconis stars and is thus a true companion star of the system.[10] Given the system's distance of 47 [light years](/source/Light_year),[11] this corresponds to a separation of at least 370 [astronomical units](/source/Astronomical_unit) between CM Draconis and GJ 630.1B.

## History of observations

CM Draconis was discovered to be an eclipsing binary by [Olin J. Eggen](/source/Olin_J._Eggen) and [Allan Sandage](/source/Allan_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](/source/Castor_(star)) C),[13] and they remained the only two known until CU Cancri ([GJ 2069](/source/GJ_2069) A) was found to be an eclipsing binary in 1999.[14]

## Search for planets

The system was the subject of a dedicated search for transiting [extrasolar planets](/source/Extrasolar_planet) 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 or [brown dwarf](/source/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.[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]

## References

1. **[^](#cite_ref-Kozhevnikova_1-0)** Kozhevnikova, A. V.; Svechnikov, M. A.; Kozhevnikov, V. P. (October 2009). "V.P. Starspot and flare activity of the dwarf system CM Dra". *Astrophysics*. **52** (4): 512–522. [Bibcode](/source/Bibcode_(identifier)):[2009Ap.....52..512K](https://ui.adsabs.harvard.edu/abs/2009Ap.....52..512K). [doi](/source/Doi_(identifier)):[10.1007/s10511-009-9090-4](https://doi.org/10.1007%2Fs10511-009-9090-4). [S2CID](/source/S2CID_(identifier)) [121618264](https://api.semanticscholar.org/CorpusID:121618264).

1. ^ [***a***](#cite_ref-GaiaDR3_2-0) [***b***](#cite_ref-GaiaDR3_2-1) [***c***](#cite_ref-GaiaDR3_2-2) [***d***](#cite_ref-GaiaDR3_2-3) Vallenari, A.; et al. (Gaia collaboration) (2023). ["*Gaia* Data Release 3. Summary of the content and survey properties"](https://doi.org/10.1051%2F0004-6361%2F202243940). *Astronomy and Astrophysics*. **674**: A1. [arXiv](/source/ArXiv_(identifier)):[2208.00211](https://arxiv.org/abs/2208.00211). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...674A...1G](https://ui.adsabs.harvard.edu/abs/2023A&A...674A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202243940](https://doi.org/10.1051%2F0004-6361%2F202243940). [S2CID](/source/S2CID_(identifier)) [244398875](https://api.semanticscholar.org/CorpusID:244398875). [Gaia DR3 record for this source](https://vizier.cds.unistra.fr/viz-bin/VizieR-4?-source=+I%2F355&-from=nav&-nav=cat%3AI%2F355%26tab%3A%7BI%2F355%2Fgaiadr3%7D%26key%3Asource%3D1355%2Fgaiadr3%26HTTPPRM%3A%26-out.add%3D.%26Source%3D%3D%3D1431176943768690816%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-SIMBAD_3-0) [***b***](#cite_ref-SIMBAD_3-1) [***c***](#cite_ref-SIMBAD_3-2) ["V* CM Dra"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+CM+Dra). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 7 May 2024.

1. ^ [***a***](#cite_ref-Morales_4-0) [***b***](#cite_ref-Morales_4-1) [***c***](#cite_ref-Morales_4-2) [***d***](#cite_ref-Morales_4-3) [***e***](#cite_ref-Morales_4-4) [***f***](#cite_ref-Morales_4-5) [***g***](#cite_ref-Morales_4-6) [***h***](#cite_ref-Morales_4-7) [***i***](#cite_ref-Morales_4-8) [***j***](#cite_ref-Morales_4-9) [***k***](#cite_ref-Morales_4-10) Morales, Juan Carlos; Ribas, Ignasi; [Jordi, Carme](/source/Carme_Jordi); Torres, Guillermo; Gallardo, José; Guinan, Edward F.; Charbonneau, David; Wolf, Marek; Latham, David W.; Anglada-Escudé, Guillem; Bradstreet, David H.; Everett, Mark E.; O'Donovan, Francis T.; Mandushev, Georgi; Mathieu, Robert D. (2009). "Absolute Properties of the Low-Mass Eclipsing Binary CM Draconis". *The Astrophysical Journal*. **691** (2): 1400–1411. [arXiv](/source/ArXiv_(identifier)):[0810.1541](https://arxiv.org/abs/0810.1541). [Bibcode](/source/Bibcode_(identifier)):[2009ApJ...691.1400M](https://ui.adsabs.harvard.edu/abs/2009ApJ...691.1400M). [doi](/source/Doi_(identifier)):[10.1088/0004-637X/691/2/1400](https://doi.org/10.1088%2F0004-637X%2F691%2F2%2F1400). [S2CID](/source/S2CID_(identifier)) [3752277](https://api.semanticscholar.org/CorpusID:3752277).

1. ^ [***a***](#cite_ref-SIMBAD2_5-0) [***b***](#cite_ref-SIMBAD2_5-1) [***c***](#cite_ref-SIMBAD2_5-2) [***d***](#cite_ref-SIMBAD2_5-3) ["EGGR 258"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=EGGR+258). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 7 May 2024.

1. ^ [***a***](#cite_ref-Kalomeni2025_6-0) [***b***](#cite_ref-Kalomeni2025_6-1) [***c***](#cite_ref-Kalomeni2025_6-2) Kalomeni, B.; Yakut, K. (2025). "Comprehensive analysis of CM Draconis: Eclipse timing variations driven by either a third body or stellar magnetic activity". [arXiv](/source/ArXiv_(identifier)):[2507.17035](https://arxiv.org/abs/2507.17035) [[astro-ph.SR](https://arxiv.org/archive/astro-ph.SR)].

1. ^ [***a***](#cite_ref-Terrien2012_7-0) [***b***](#cite_ref-Terrien2012_7-1) Terrien, Ryan C.; Fleming, Scott W.; et al. (November 2012). "The Metallicity of the CM Draconis System". *[The Astrophysical Journal Letters](/source/The_Astrophysical_Journal_Letters)*. **760** (1): L9. [arXiv](/source/ArXiv_(identifier)):[1210.4736](https://arxiv.org/abs/1210.4736). [Bibcode](/source/Bibcode_(identifier)):[2012ApJ...760L...9T](https://ui.adsabs.harvard.edu/abs/2012ApJ...760L...9T). [doi](/source/Doi_(identifier)):[10.1088/2041-8205/760/1/L9](https://doi.org/10.1088%2F2041-8205%2F760%2F1%2FL9).

1. **[^](#cite_ref-Martin2024_8-0)** Martin, David V.; Sethi, Ritika; et al. (February 2024). ["The benchmark M dwarf eclipsing binary CM Draconis with TESS: spots, flares, and ultra-precise parameters"](https://doi.org/10.1093%2Fmnras%2Fstae015). *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*. **528** (1): 963–975. [arXiv](/source/ArXiv_(identifier)):[2301.10858](https://arxiv.org/abs/2301.10858). [Bibcode](/source/Bibcode_(identifier)):[2024MNRAS.528..963M](https://ui.adsabs.harvard.edu/abs/2024MNRAS.528..963M). [doi](/source/Doi_(identifier)):[10.1093/mnras/stae015](https://doi.org/10.1093%2Fmnras%2Fstae015).

1. **[^](#cite_ref-9)** Samus (2004). ["CM Dra"](http://webviz.u-strasbg.fr/viz-bin/VizieR-S?V*%20CM%20Dra). *Combined General Catalogue of Variable Stars*.

1. ^ [***a***](#cite_ref-deeg08_10-0) [***b***](#cite_ref-deeg08_10-1) 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. [arXiv](/source/ArXiv_(identifier)):[0801.2186](https://arxiv.org/abs/0801.2186). [Bibcode](/source/Bibcode_(identifier)):[2008A&A...480..563D](https://ui.adsabs.harvard.edu/abs/2008A&A...480..563D). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20079000](https://doi.org/10.1051%2F0004-6361%3A20079000). [S2CID](/source/S2CID_(identifier)) [10252705](https://api.semanticscholar.org/CorpusID:10252705).

1. **[^](#cite_ref-gliese91_11-0)** Gliese, W.; Jahreiß, H. (1991). ["GJ 630.1A"](http://webviz.u-strasbg.fr/viz-bin/VizieR-S?GJ%20630.1%20A). *Preliminary Version of the Third Catalogue of Nearby Stars*. Retrieved 2008-10-12.

1. **[^](#cite_ref-EggenSandage1967_12-0)** Eggen, Olin J.; Sandage, Allan (June 1967). "Examination of the Evidence for the Existence of Pygmy Stars". *[Astrophysical Journal](/source/Astrophysical_Journal)*. **148**: 911. [Bibcode](/source/Bibcode_(identifier)):[1967ApJ...148..911E](https://ui.adsabs.harvard.edu/abs/1967ApJ...148..911E). [doi](/source/Doi_(identifier)):[10.1086/149215](https://doi.org/10.1086%2F149215).

1. **[^](#cite_ref-Lacy1977_13-0)** Lacy, C. H. (December 1977). "Absolute dimensions and masses of the remarkable spotted dM4e eclipsing binary flare star CM Draconis". *[Astrophysical Journal](/source/Astrophysical_Journal)*. **218**: 444–460. [Bibcode](/source/Bibcode_(identifier)):[1977ApJ...218..444L](https://ui.adsabs.harvard.edu/abs/1977ApJ...218..444L). [doi](/source/Doi_(identifier)):[10.1086/155698](https://doi.org/10.1086%2F155698).

1. **[^](#cite_ref-Delfosse1999a_14-0)** Delfosse, X.; Forveille, T.; et al. (January 1999). "GJ 2069A, a new M dwarf eclipsing binary". *[Astronomy and Astrophysics](/source/Astronomy_and_Astrophysics)*. **341**: L63–L66. [Bibcode](/source/Bibcode_(identifier)):[1999A&A...341L..63D](https://ui.adsabs.harvard.edu/abs/1999A&A...341L..63D).

1. **[^](#cite_ref-tep_15-0)** ["The TEP network"](http://www.iac.es/project/tep/tephome.html).

1. **[^](#cite_ref-16)** 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. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0001177](https://arxiv.org/abs/astro-ph/0001177). [Bibcode](/source/Bibcode_(identifier)):[2000ApJ...535..338D](https://ui.adsabs.harvard.edu/abs/2000ApJ...535..338D). [doi](/source/Doi_(identifier)):[10.1086/308830](https://doi.org/10.1086%2F308830). [S2CID](/source/S2CID_(identifier)) [18639250](https://api.semanticscholar.org/CorpusID:18639250).

1. **[^](#cite_ref-17)** Deeg, Hans J.; Doyle, Laurance R.; Kozhevnikov, Valerij P.; Blue, J. Ellen; Martín, Eduardo L.; Schneider, Jean (2000). "A search for Jovian-mass planets around CM Draconis using eclipse minima timing". *Astronomy and Astrophysics*. **358**: L5–L8. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0003391](https://arxiv.org/abs/astro-ph/0003391). [Bibcode](/source/Bibcode_(identifier)):[2000A&A...358L...5D](https://ui.adsabs.harvard.edu/abs/2000A&A...358L...5D).

## External links

- ["CM Draconis 3"](https://web.archive.org/web/20020420065226/http://solstation.com/stars2/cm-dra3.htm#cmdra-aa). *SolStation*. Archived from [the original](http://www.solstation.com/stars2/cm-dra3.htm#cmdra-aa) on April 20, 2002. Retrieved 2008-06-11.

v t e Constellation of Draco List of stars in Draco Draco in Chinese astronomy Stars Bayer α (Thuban) β (Rastaban) γ (Eltanin) δ (Altais) ε (Tyl) ζ (Aldhibah) η (Athebyne) θ ι (Edasich) κ λ (Giausar) μ (Alrakis) ν (Kuma) ξ (Grumium) ο π ρ σ (Alsafi) τ υ φ χ ψ1 (Dziban) ψ2 ω Flamsteed 4 6 7 (Tianyi) 8 (Taiyi) 10 (i) 15 (A) 18 (g) 19 (h) 26 36 39 (b) 42 (Fafnir) 45 (d) 50 59 64 (e) 68 Variable TW YY AG BY CL CM CX DO EK HP V581 HR 3751 4126 4934 5811 6237 6518 6618 (Alruba) 6817 7137 7783 HD 109246 (Funi) 101364 128717 147379 156279 158259 176693 191939 Other 2MASS 1237+6526 2MASS J17554042+6551277 G 240-72 GD 356 Gliese 420 Gliese 625 Gliese 687 GRW +70 8247 Kepler-4 Kepler-10 Kepler-12 Kepler-90 Kepler-296 KOI-256 LP 71-82 Qatar-1 SDSS J1240+6710 Struve 2398 TOI-1136 WD 1856+534 WISE 1647+5632 WISE 1841+7000 Exoplanets HD 139357 b HD 167042 b ι Dra b (Hypatia) Kepler-4b Kepler-10b c Kepler-12b Kepler-90e f g h i Kepler-296b c d e f TOI-1452 b TrES-2b Star clusters LAMOST 1 Nebulae Cat's Eye Nebula NGC 6742 Galaxies NGC 3147 3197 3735 4121 4125 4221 4236 4319 4331 4332 4363 4441 4513 4545 4589 5678 5777 5866 5866B 5879 5905 5907 5949 5963 5965 5982 5985 6090 6248 6285 6286 6338 6340 6365 6373 6394 6412 6503 6505 6566 6621 6622 6670 6676 6786 6789 Other 1ES 1927+654 1ES 1959+650 3C 249.1 3C 305 3C 319 3C 343 3C 343.1 3C 351 3C 356 3C 371 3C 380 3C 390.3 3C 401 4C +72.26 4C 73.08 8C 1241+735 Abell 2218 BCG Bean galaxy Beaver galaxy BZQ J1727+5510 Draco Dwarf Draco II GB 1508+5714 Goldfish galaxy H1821+643 HFLS3 IERS B1946+708 IRAS F17179+5444 IRAS 18580+6527 J120011.1+680924.8 KKR 25 Markarian 817 Markarian 876 Original TRG PGC 39058 Porphyrion QSO B1823+568 RGZ J172749.5+534647 S5 1803+784 S5 2007+777 SDSS J1715+6008 Tadpole Galaxy UGC 9391 UGC 9405 UGC 11241 UGC 11411 WISEA J145223.62+611707.5 WN B1851+5707 Galaxy clusters Abell 2218 CL1358+62 Draco Supercluster NGC 5866 Group Astronomical events SN 2003jb SN 2005B SN 2016aps Swift J1644+57 Category

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Adapted from the Wikipedia article [CM Draconis](https://en.wikipedia.org/wiki/CM_Draconis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/CM_Draconis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.