ABSTRACT
Table (7-6) in Kopal's (1959) book listed 18 eclipsing binary systems characterized by light curves whose deeper (primary) minimum was that of a normal Main-Sequence-like star, while the secondary minimum corresponded to the eclipse of a cooler star of comparable, if not greater, size, yet significantly smaller than its surrounding Roche lobe. Such binaries, having normal primaries and swollen secondaries, sometimes called subgiants, were originally regarded as within the broad spectrum of Algol-like systems. Kopal referred to this particular subgrouping as the ‘undersize Algols’. In some cases, a spectroscopically determined mass ratio q was available, and that was often close to unity.
