CM Draconis

{{Short description|Star in the constellation Draco}} {{Sky|16|34|20.321|+|57|09|44.70|47.1}} {{Starbox begin | name = CM Draconis }} {{Starbox image | image = [[Image:CMDraLightCurve.png|250px]] | caption = A [[Photometric_system#Photometric_letters|red band]] [[light curve]] for CM Draconis, adapted from Kozhevnikova ''et al.'' (2009)<ref name="Kozhevnikova"/> }} {{Starbox observe | epoch = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Draco (constellation)|Draco]] | ra = {{RA|16|34|20.33027}}<ref name=GaiaDR3/> | dec = {{DEC|+57|09|44.3689}}<ref name=GaiaDR3/> | appmag_v = 12.87<ref name=SIMBAD/> }} {{Starbox character | class = M4.5V / M4.5V<ref name=Morales/> / DQ8<ref name=SIMBAD2/> | variable =[[BY Draconis variable]]<br/>[[Eclipsing binary]]<br/>[[Flare star]] }} {{Starbox astrometry | radial_v = –118.24<ref name=SIMBAD/> | prop_mo_ra = –1113.797 | prop_mo_dec = 1180.977 | pm_footnote = <ref name=GaiaDR3/> | parallax = 67.2876 | p_error = 0.0337 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = 12.1{{cn|date=May 2024}} }} {{Starbox orbit |reference=<ref name=Kalomeni2025/> |period_unitless={{val|1.268390011|(3)|ul=d}} |axis_unitless={{val|3.6712|0.0053|ul=solar radius}} |eccentricity={{val|0.0038|0.0031}} |inclination={{val|89.96|0.06}} |node=15.79<ref name=Morales/> |periarg={{val|119|3}} |k1=72.23<ref name=Morales/> |k2=77.95<ref name=Morales/> }} {{Starbox detail |source=<ref name=Kalomeni2025/> |component1=Aa |mass={{val|0.2307|0.0008}} |radius={{val|0.2638|0.0011}} |luminosity={{val|0.0060|0.0005}} |gravity={{val|4.959|0.006}} |temperature=3130 ± 70<ref name=Morales/> |metal_fe={{val|−0.30|0.12}}<ref name="Terrien2012"/> |age_gyr=4.1 ± 0.8<ref name=Morales/> |component2=Ab |mass2={{val|0.2136|0.0008}} |radius2={{val|0.2458|0.0010}} |luminosity_bolometric2={{val|0.0050|0.0004}} |gravity2={{val|4.959|0.006}} |temperature2=3120 ± 70<ref name=Morales/> |metal_fe2={{val|−0.30|0.12}}<ref name="Terrien2012"/> |age_gyr2=4.1 ± 0.8<ref name=Morales/> }} {{Starbox detail|no_heading=y | component1=B | mass={{val|0.58}}<ref name=SIMBAD2/> | temperature=6126<ref name=SIMBAD2/> }} {{Starbox catalog |component1=Eclipsing binary |names1={{odlist | V=CM Dra | CCDM=J16343+5710A | GJ=630.1A | LHS=421 | LP=101-15 | NLTT=43148 | TIC=199574208 | WDS=J16345+5709A}}<ref name=SIMBAD/> |component2=White dwarf |names2={{odlist | CCDM=J16343+5710B | EGGR=258 | GJ=630.1B | LHS=422 | LP=101-16 | NLTT=43149 | TIC=199574211 | WD=1633+572 | WDS=J16345+5709B}}<ref name=SIMBAD2/> }} {{Starbox reference |Simbad=CM+Dra|sn=A |Simbad2=EGGR+258|sn2=B |ARICNS=01315|an=A |ARICNS2=01316|an2=B }} {{Starbox end}}

'''CM Draconis''' (GJ 630.1A) is an [[eclipsing binary]] star system {{convert|48.5|ly|pc|lk=on|abbr=off}} away in the [[constellation]] of [[Draco (constellation)|Draco]] (the [[Dragon]]). The system consists of two nearly identical [[red dwarf]] stars that orbit each other with a period of 1.268 [[day]]s and a separation of 2.6 million kilometres (0.017 AU).<ref name="Martin2024"/> Along with two stars in the triple system [[Kepler Object of Interest#Non-planet discoveries|KOI-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.<ref name="Morales"/> These comparisons find that models underpredict the stellar radii by approximately 5%. This is attributed to consequences of the stars' strong magnetic activity.<ref name=Morales/>

According to the system's entry in the [[General Catalogue of Variable Stars|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]].<ref>{{cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-S?V*%20CM%20Dra|title=CM Dra|work=Combined General Catalogue of Variable Stars|author=Samus|year=2004}}</ref> The [[white dwarf]] star '''GJ 630.1B''', also known as '''WD 1633+572''', located 25.7 [[arcsecond]]s away shares the same [[proper motion]] as the CM Draconis stars and is thus a true companion star of the system.<ref name="deeg08">{{cite journal|bibcode=2008A&A...480..563D |title=Extrasolar planet detection by binary stellar eclipse timing: evidence for a third body around CM Draconis|author1=Deeg, H. J. |author2=Ocaña, B. |author3=Kozhevnikov, V. P. |author4=Charbonneau, D. |author5=O'Donovan, F. T. |author6=Doyle, L. R. |journal=Astronomy and Astrophysics|volume=480|issue=2|pages=563–571|year=2008|doi=10.1051/0004-6361:20079000|arxiv = 0801.2186 |s2cid=10252705}}</ref> Given the system's distance of 47 [[light year]]s,<ref name="gliese91">{{cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-S?GJ%20630.1%20A|title=GJ 630.1A|work=Preliminary Version of the Third Catalogue of Nearby Stars|author1=Gliese, W. |author2=Jahreiß, H.|year=1991|accessdate=2008-10-12}}</ref> this corresponds to a separation of at least 370 [[astronomical unit]]s 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.<ref name="EggenSandage1967"/> It was the second M-dwarf eclipsing binary discovered after YY Geminorum ([[Castor (star)|Castor]] C),<ref name="Lacy1977"/> and they remained the only two known until CU Cancri ([[GJ 2069]] A) was found to be an eclipsing binary in 1999.<ref name="Delfosse1999a"/>

== Search for planets == The system was the subject of a dedicated search for transiting [[extrasolar planet]]s 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.<ref name="tep">{{cite web|url=http://www.iac.es/project/tep/tephome.html|title=The TEP network}}</ref><ref>{{cite journal|bibcode=2000ApJ...535..338D|title=Observational Limits on Terrestrial-sized Inner Planets around the CM Draconis System Using the Photometric Transit Method with a Matched-Filter Algorithm|author1=Doyle, Laurance R. |author2=Deeg, Hans J. |author3=Kozhevnikov, Valerij P. |author4=Oetiker, Brian |author5=Martín, Eduardo L. |author6=Blue, J. Ellen |author7=Rottler, Lee |author8=Stone, Remington P. S. |author9=Ninkov, Zoran |author10=Jenkins, Jon M. |author11=Schneider, Jean |author12=Dunham, Edward W. |author13=Doyle, Moira F. |author14=Paleologou, Efthimious |journal=The Astrophysical Journal|volume=535|issue=1|pages=338–349|year=2000|doi=10.1086/308830|arxiv = astro-ph/0001177 |s2cid=18639250}}</ref>

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.<ref>{{cite journal|bibcode=2000A&A...358L...5D|title=A search for Jovian-mass planets around CM Draconis using eclipse minima timing |author1=Deeg, Hans J. |author2=Doyle, Laurance R. |author3=Kozhevnikov, Valerij P. |author4=Blue, J. Ellen |author5=Martín, Eduardo L. |author6=Schneider, Jean |journal=Astronomy and Astrophysics |volume=358|pages=L5–L8|year=2000|arxiv = astro-ph/0003391 }}</ref> 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.<ref name="deeg08" /> 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.<ref name="Morales"/>

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.<ref name=Kalomeni2025/>

== References ==

<references> <ref name=Kalomeni2025>{{cite arXiv|last1=Kalomeni |first1=B. |last2=Yakut |first2=K. |title=Comprehensive analysis of CM Draconis: Eclipse timing variations driven by either a third body or stellar magnetic activity |date=2025 |class=astro-ph.SR |eprint=2507.17035}}</ref>

<ref name=SIMBAD>{{cite simbad |title=V* CM Dra |access-date=7 May 2024}}</ref> <ref name=SIMBAD2>{{cite simbad |title=EGGR 258 |access-date=7 May 2024}}</ref>

<ref name="EggenSandage1967">{{cite journal |last1=Eggen |first1=Olin J. |last2=Sandage |first2=Allan |date=June 1967 |title=Examination of the Evidence for the Existence of Pygmy Stars |journal=[[Astrophysical Journal]] |volume=148 |issue= |page=911 |doi=10.1086/149215 |bibcode=1967ApJ...148..911E}}</ref>

<ref name="Lacy1977">{{cite journal |last1=Lacy |first1=C. H. |date=December 1977 |title=Absolute dimensions and masses of the remarkable spotted dM4e eclipsing binary flare star CM Draconis. |journal=[[Astrophysical Journal]] |volume=218 |issue= |pages=444–460 |doi=10.1086/155698 |bibcode=1977ApJ...218..444L}}</ref>

<ref name="Delfosse1999a">{{cite journal |last1=Delfosse |first1=X. |last2=Forveille |first2=T. |display-authors=etal |date=January 1999 |title=GJ 2069A, a new M dwarf eclipsing binary |journal=[[Astronomy and Astrophysics]] |volume=341 |issue= |pages=L63–L66 |bibcode=1999A&A...341L..63D}}</ref>

<ref name="Morales">{{cite journal|title=Absolute Properties of the Low-Mass Eclipsing Binary CM Draconis|author1=Morales, Juan Carlos |author2=Ribas, Ignasi |author3=Jordi, Carme|author3-link=Carme Jordi |author4=Torres, Guillermo |author5=Gallardo, José |author6=Guinan, Edward F. |author7=Charbonneau, David |author8=Wolf, Marek |author9=Latham, David W. |author10=Anglada-Escudé, Guillem |author11=Bradstreet, David H. |author12=Everett, Mark E. |author13=O'Donovan, Francis T. |author14=Mandushev, Georgi |author15=Mathieu, Robert D. |year=2009|journal=The Astrophysical Journal|volume=691|issue=2|pages=1400–1411|doi=10.1088/0004-637X/691/2/1400|bibcode=2009ApJ...691.1400M|arxiv=0810.1541|s2cid=3752277 }}</ref>

<ref name="Kozhevnikova">{{cite journal |last1=Kozhevnikova |first1=A. V. |last2=Svechnikov |first2=M. A. |last3=Kozhevnikov |first3=V. P. |title=V.P. Starspot and flare activity of the dwarf system CM Dra |journal=Astrophysics |date=October 2009 |volume=52 |issue=4 |pages=512–522 |doi=10.1007/s10511-009-9090-4 |bibcode=2009Ap.....52..512K |s2cid=121618264 }}</ref>

<ref name="Terrien2012">{{cite journal |last1=Terrien |first1=Ryan C. |last2=Fleming |first2=Scott W. |display-authors=etal |date=November 2012 |title=The Metallicity of the CM Draconis System |journal=[[The Astrophysical Journal Letters]] |volume=760 |issue=1 |pages=L9 |doi=10.1088/2041-8205/760/1/L9 |arxiv=1210.4736 |bibcode=2012ApJ...760L...9T}}</ref>

<ref name="Martin2024">{{cite journal |last1=Martin |first1=David V. |last2=Sethi |first2=Ritika |display-authors=etal |date=February 2024 |title=The benchmark M dwarf eclipsing binary CM Draconis with TESS: spots, flares, and ultra-precise parameters |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=528 |issue=1 |pages=963–975 |doi=10.1093/mnras/stae015 |doi-access=free |arxiv=2301.10858 |bibcode=2024MNRAS.528..963M}}</ref> </references>

== External links ==

* {{cite web |url=http://www.solstation.com/stars2/cm-dra3.htm#cmdra-aa |archive-url=https://web.archive.org/web/20020420065226/http://solstation.com/stars2/cm-dra3.htm#cmdra-aa |url-status=dead |archive-date=April 20, 2002 |title=CM Draconis 3 |accessdate=2008-06-11 |work=SolStation}} {{Clear}}

[[Category:Draco (constellation)]] [[Category:BY Draconis variables]] [[Category:Flare stars]] [[Category:Eclipsing binaries]] [[Category:Triple star systems]] [[Category:M-type main-sequence stars]] [[Category:White dwarfs]] [[Category:Gliese and GJ objects|0630.1]] [[Category:Objects with variable star designations|Draconis, CM]]