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 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.[1]
A light curve for W Ursae Majoris, the class prototype, plotted from TESS data[2]
The class is divided into two subclasses: A-type and W-type.[3] A-type W UMa binaries are composed of two stars both hotter than the Sun, having spectral types A or F, and 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 kelvins. 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.
[4] The H-types have a higher mass ratio than ( = (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.[5] In 2012, Terrell, Gross and Cooney published a color-survey of 606 W UMa systems in the Johnson-Cousins photometric system.[6]
Their light curves differ from those of classical eclipsing binaries, undergoing a constant ellipsoidal variation rather than discrete eclipses. 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 minima are usually equal because both stars have nearly equal surface temperatures.
W Ursae Majoris is the prototype of this class.
This is a dynamic list and may never be able to satisfy particular standards for completeness. You can help by adding missing items with reliable sources.
Designation (name)
Constellation
Discovery
Apparent magnitude (Maximum)[a]
Apparent magnitude (Minimum)[a]
Range of magnitude
Period
Spectral types (eclipsing components)
Comment
AB And
Andromeda
10.40
11.27
0.87
0.3319 d
G5
G5V
S Ant
Antlia
H.M.Paul, 1891
6.27
6.83
0.56
0.6483489 d
A9V
A9V
44 (or i) Boo B
Boötes
5.8
6.4
0.6
0.2678159 d
G2V
G2V
Triple system, A being non-variable
TU Boo
Boötes
11.8
12.5
0.7
0.324 d
VW Cep
Cepheus
7.23
7.68
0.45
0.278 d
G5
K0Ve
WZ Cep
Cepheus
11.4
12.0
0.6
0.41744 d
F5
Possible triple system
ε CrA
Corona Australis
4.74
5.0
0.26
0.5914264 d
SX Crv
Corvus
8.99
9.25
0.26
0.32 d
F7V
?
V1191 Cyg
Cygnus
10.82
11.15
0.33
0.31 d
F6V
G5V
V571 Dra
Draco
Barquin, 2018
14.43
14.77
0.34
0.428988 d
XY Leo
Leo
9.45
9.93
0.48
0.284 d
K0V
K0
CE Leo
Leo
11.8
12.6
0.8
0.303 d
TV Pic
Pictor
Verschuren, 1987
7.37
7.53
0.16
0.85 d
A2V
A9-F0V
Y Sex
Sextans
9.81
10.23
0.42
0.42 d
F3/5V[4] or F5/6V
Possibly two substellar companions
W UMa
Ursa Major
7.75
8.48
0.73
0.3336 d
F8Vp
F8Vp
Prototype, possible triple system
^Wilson, R. E. (2001). "Binary Star Morphology and the Name Overcontact". Information Bulletin on Variable Stars. 5076: 1. Bibcode:2001IBVS.5076....1W.
^Cite error: The named reference MAST was invoked but never defined (see the help page).
^Remeis-Sternwarte (1965). "Veraenderlichen Colloquium : 3 : 1965". Kleine Veroeffentlichungen der Remeis-Sternwarte Bamberg. Bibcode:1965veco.conf.....R.
^Sz. Csizmadia and P. Klagyivik (18 October 2004). "On the properties of contact binary stars". Astronomy and Astrophysics. 426 (3): 1001–1005. arXiv:astro-ph/0408049. Bibcode:2004A&A...426.1001C. doi:10.1051/0004-6361:20040430.
^"Contact Binaries II". Memoirs of the Royal Astronomical Society. 70: 111. 1967. Bibcode:1967MmRAS..70..111E.
^
Terrell, Dirk; Gross, John; Cooney, Walter (2012). "A BVRCIC Survey of W Ursae Majoris Binaries". Astronomical Journal. 143 (4): 99. arXiv:1202.3111. Bibcode:2012AJ....143...99T. doi:10.1088/0004-6256/143/4/99. S2CID 118622542.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).
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