W Ursae Majoris variable

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.

[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.

In 2004 the H (high mass ratio) systems were discovered by Szilárd Csizmadia and Peter Klagyivik.

These stars were first shown to follow a period-color relation (shorter period systems are redder) by Olin J.

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 light curve for W Ursae Majoris, the class prototype, plotted from TESS data [ 2 ]