Period Changes in Four Algol-Type Binaries: SX Dra, AV Del, CU Peg and DK Peg

Orbital period changes of four neglected short-period semidetached Algols, SX Dra, AV Del, CU Peg and DK Peg, are presented based on the analysis of their O–C observations. It is found that the three systems, AV Del, CU Peg and DK Peg, show rapid period increase at rates of dP/dt =+3.15 × 10^-6, +2.00 × 10^-6 and +4.88 × 10^-7days/year respectively. For the other system, SX Dra, a possible periodic variation in the orbital period is discovered to superimpose on a very rapid period increase (dP/dt = +1.09 × 10^-5 days/year). The period increases of the four Algols can be explained by a mass transfer from the secondary to the more massive primary, which is in agreement with the semi-detached configurations of these systems. However, since the period increases are rather rapid, the mass transfer should be on a dynamical time scale. The cyclic period change in SX Dra suggests that there may exist a third body in this system. This revised version was published online in July 2006 with corrections to the Cover Date.