View source for W Ursae Majoris variable

[[File:Binary star system - contact configuration q=3.svg|thumb|Schematic of a W Ursae Majoris variable with a mass ratio of 3. Both stars (the filled regions) overfill their Roche lobes (enclosed by the black lines).]]

A '''W Ursae Majoris variable''', also known as a '''low mass contact binary''', is a type of [[eclipsing binary]] [[variable star]]. These stars are close binaries of spectral types F, G, or K that share a common envelope of material and are thus in contact with one another.  They are termed [[contact binary|contact binaries]] because the two stars touch and transfer mass and energy through the connecting neck, although astronomer Robert E. Wilson argues that the term "overcontact" is more appropriate.<ref name="wilson2001">{{cite journal|last1=Wilson |first1=R. E.|date=2001|title=Binary Star Morphology and the Name Overcontact|journal=Information Bulletin on Variable Stars|volume=5076 |pages=1|bibcode=2001IBVS.5076....1W}}</ref>

[[File:WUMaLightCurve.png|thumb|left|A [[light curve]] for W Ursae Majoris, the class prototype, plotted from ''[[Transiting Exoplanet Survey Satellite|TESS]]'' data<ref name=MAST/>]]
The class is divided into two subclasses: A-type and W-type.<ref>{{cite journal |bibcode=1965veco.conf.....R |title=Veraenderlichen Colloquium : 3 : 1965 |author1=Remeis-Sternwarte |journal=Kleine Veroeffentlichungen der Remeis-Sternwarte Bamberg |year=1965 }}</ref> A-type W UMa binaries are composed of two stars both hotter than the Sun, having [[stellar classification|spectral types]] A or F, and [[orbital period|periods]] of 0.4 to 0.8 day.  The W-types have cooler spectral types of G or K and shorter periods of 0.22 to 0.4 day. The difference between the surface temperatures of the components is less than several hundred [[kelvin]]s. A new subclass was introduced in 1978: B-type. The B-types have larger surface temperature difference. In 2004 the H (high mass ratio) systems were discovered by Szilárd Csizmadia and Peter Klagyivik.
<ref name=Csizmadia>{{cite journal|author= Sz. Csizmadia and P. Klagyivik |title=On the properties of contact binary stars |journal=Astronomy and Astrophysics |volume=426 |pages=1001–1005 |date=18 October 2004 |issue=3 |doi=10.1051/0004-6361:20040430|arxiv=astro-ph/0408049 |bibcode=2004A&A...426.1001C |doi-access=free }}</ref> The H-types have a higher mass ratio than <math>q=0.72</math> (<math>q</math> = (secondary's mass)/(primary's mass)) and they have extra [[angular momentum]].

These stars were first shown to follow a period-color relation (shorter period systems are redder) by [[Olin J. Eggen]].<ref name="eggen1967">{{Cite journal|title=Contact Binaries II|bibcode=1967MmRAS..70..111E|date=1967|journal=Memoirs of the Royal Astronomical Society|volume=70|pp=111}}</ref> In 2012, [[Dirk Terrell|Terrell]], Gross and [[Walter R. Cooney Jr.|Cooney]] published a color-survey of 606 W UMa systems in the [[UBV photometric system|Johnson]]-Cousins [[photometric system]].<ref name="tgc2012">
{{cite journal|last1=Terrell |first1=Dirk|last2=Gross|first2=John|last3=Cooney|first3=Walter|date=2012|title=A ''BVR<sub>C</sub>I<sub>C</sub>'' Survey of W Ursae Majoris Binaries|journal=Astronomical Journal|volume=143 |issue=4|pages=99|bibcode=2012AJ....143...99T|arxiv = 1202.3111 |doi = 10.1088/0004-6256/143/4/99 |s2cid=118622542}}</ref>

Their light curves differ from those of classical [[eclipsing binary|eclipsing binaries]], undergoing a constant ellipsoidal variation rather than discrete [[eclipse]]s.  This is because the stars are gravitationally distorted by one another, and thus the projected area of the stars is constantly changing.  The depths of the brightness [[minimum|minima]] are usually equal because both stars have nearly equal surface [[temperature]]s.

[[W Ursae Majoris]] is the prototype of this class.

{{dynamic list}}
{| class="wikitable sortable" style="font-size:90%; bold"
|- bgcolor="#efefef"
! width="10%"| Designation (name)
! width="10%"| Constellation
! width="8%"| Discovery
! width="8%"|''[[Apparent magnitude]]'' (Maximum){{efn|name=note1}}
! width="8%"|''[[Apparent magnitude]]'' (Minimum){{efn|name=note1}}
! width="8%"|''Range of magnitude''
! width="11%"| Period
!colspan=2 width="19%"| Spectral types<br/><small>(eclipsing components)</small>
! width="20%"|Comment
|---
| [[AB Andromedae|AB And]]
| [[Andromeda (constellation)|Andromeda]]
| &nbsp;
| {{ntsh|10.40}}10.40
| {{ntsh|11.27}}11.27
| {{nts|0.87}}
| {{nts|0.3319}}&nbsp;d
| style="background:#{{Color temperature|5600|hexval}};"| G5 
| style="background:#{{Color temperature|5600|hexval}};"| G5V
|
|---
| [[S Antliae|S Ant]]
| [[Antlia]]
| H.M.Paul, 1891
| {{ntsh|6.27}}6.27
| {{ntsh|6.83}}6.83
| {{nts|0.56}}
| {{nts|0.6483489}}&nbsp;d
| style="background:#{{Color temperature|7800|hexval}};"|A9V
| style="background:#{{Color temperature|7340|hexval}};"|A9V
| 
|---
| [[44 Boötis|44]] (or i) Boo B
| [[Boötes]]
| &nbsp;
| {{ntsh|5.8}}5.8
| {{ntsh|6.4}}6.4
| {{nts|0.6}}
| {{nts|0.2678159}}&nbsp;d
| style="background:#{{Color temperature|5600|hexval}};"| G2V
| style="background:#{{Color temperature|5600|hexval}};"| G2V
| Triple system, A being non-variable
|---
|[[TU Boötis|TU Boo]]
|[[Boötes]]
|&nbsp;
|{{ntsh|11.8}}11.8
|{{ntsh|12.5}}12.5
|{{nts|0.7}}
| {{nts|0.324}}&nbsp;d
|
|
|
|---
| [[VW Cephei|VW Cep]]
| [[Cepheus (constellation)|Cepheus]]
| &nbsp;
| {{ntsh|7.23}}7.23
| {{ntsh|7.68}}7.68
| {{nts|0.45}}
| {{nts|0.278}}&nbsp;d
| style="background:#{{Color temperature|5600|hexval}};"|G5
| style="background:#{{Color temperature|4450|hexval}};"|K0Ve
| 
|---
| [[WZ Cephei|WZ Cep]]
| [[Cepheus (constellation)|Cepheus]]
| &nbsp;
| {{ntsh|11.4}}11.4
| {{ntsh|12.0}}12.0
| {{nts|0.6}}
| {{nts|0.41744}}&nbsp;d
| style="background:#{{Color temperature|6750|hexval}};"|F5
| 
| Possible triple system
|---
| [[Epsilon Coronae Australis|ε CrA]]
| [[Corona Australis]]
| &nbsp;
| {{ntsh|4.74}}4.74
| {{ntsh|5}}5.0
| {{nts|0.26}}
| {{nts|0.5914264}}&nbsp;d
|  
|
| 
|---
| [[SX Corvi|SX Crv]]
| [[Corvus (constellation)|Corvus]]
| 
| {{ntsh|8.99}}8.99
| {{ntsh|9.25}}9.25
| {{nts|0.26}}
| {{nts|0.32}}&nbsp;d
| style="background:#{{Color temperature|6750|hexval}};"|F7V
|?
|
|---
| [[V1191 Cygni|V1191 Cyg]]
| [[Cygnus (constellation)|Cygnus]]
| 
| {{ntsh|10.82}}10.82
| {{ntsh|11.15}}11.15
| {{nts|0.33}}
| {{nts|0.31}}&nbsp;d
| style="background:#{{Color temperature|6750|hexval}};"|F6V
| style="background:#{{Color temperature|5600|hexval}};"|G5V
|
|---
| [[V571 Draconis|V571 Dra]]
| [[Draco (constellation)|Draco]]
| Barquin, 2018
| {{ntsh|14.43}}14.43
| {{ntsh|14.77}}14.77
| {{nts|0.34}}
| {{nts|0.428988}}&nbsp;d
|
|
|
|---
| [[XY Leonis|XY Leo]]
| [[Leo (constellation)|Leo]]
| &nbsp;
|{{ntsh|9.45}}9.45
|{{ntsh|9.93}}9.93
|{{nts|0.48}}
|{{nts|0.284}}&nbsp;d
| style="background:#{{Color temperature|4450|hexval}};"|K0V 
| style="background:#{{Color temperature|4450|hexval}};"|K0
|
|---
|[[CE Leonis|CE Leo]]
|[[Leo (constellation)|Leo]]
|&nbsp;
|{{ntsh|11.8}}11.8
|{{ntsh|12.6}}12.6
|{{nts|0.8}}
|{{nts|0.303}}&nbsp;d
|
|
|
|---
| [[TV Pictoris|TV Pic]]
| [[Pictor]]
| Verschuren, 1987
| {{ntsh|7.37}}7.37
| {{ntsh|7.53}}7.53
| {{nts|0.16}}
| {{nts|0.85}}&nbsp;d
| style="background:#{{Color temperature|7800|hexval}};"|A2V
| style="background:#{{Color temperature|7800|hexval}};"|A9-F0V
|
|---
| [[Y Sextantis|Y Sex]]
| [[Sextans]]
| 
| {{ntsh|9.81}}9.81
| {{ntsh|10.23}}10.23
| {{nts|0.42}}
| {{nts|0.42}}&nbsp;d
| F3/5V[4] or F5/6V
|
| Possibly two substellar companions
|---
| [[W Ursae Majoris|W UMa]]
| [[Ursa Major]]
| &nbsp;
| {{ntsh|7.75}}7.75
| {{ntsh|8.48}}8.48
| {{nts|0.73}}
| {{nts|0.3336}}&nbsp;d
| style="background:#{{Color temperature|6750|hexval}};"|F8Vp 
| style="background:#{{Color temperature|6750|hexval}};"|F8Vp
| Prototype, possible triple system
|----
|}

==Notes==
{{notelist|refs=

{{efn|name=note1|1=''(visual magnitude, unless marked'' (B) ''(= blue) or'' (p) ''(= photographic))''}}

}}

== References ==
{{Reflist|1|refs=

<ref name=MAST>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=8 December 2021}}</ref>

}}

== External links ==
*[https://ogle.astrouw.edu.pl/atlas/EW.html OGLE Atlas of Variable Star Light Curves - W Ursae Majoris type binaries]

{{Variable star topics}}

{{DEFAULTSORT:W Ursae Majoris Variable}}
[[Category:W Ursae Majoris variables| ]]