Classes of Eclipsing Binaries and the Roche Lobe

Abstract

The general pattern of light curves as shown by the ‘typical’ examples in Figure 23 readily suggested that three classes of eclipsing binaries are to be distinguished:

• EA Algol type: the light is fairly constant outside of eclipses. As this constancy strictly holds only in the revolution of two spherical bodies with isotropic surface area brightnesses, the stars are thought to approximate this simple model. Beginning and end of eclipses are fairly well-defined. As a rule, primary and secondary minima have unequal depths.

• EB ß Lyrae type: The light varies also outside the eclipses, often to an extent that the duration of the eclipses is not even approximately seen. Causes are the deformation of the stars into bodies without rotational symmetry, and differences of brightness between various parts of the surfaces. The ‘rectification’ of the light curve (p. 110) purports to reduce the analysis of these features to the proceeding, simpler case.

• EW W Ursae Maioris type: it was formed as a sub-group of closely related light curves within the ß Lyr class. Characteristic features are the shorter periods (less than 1 day) and the frequently almost equal depths of primary and secondary minima. Eclipses cover a considerable fraction of the period although their duration is not readily determined from the light curve.