Orbital Period Studies of Two Algol‐Type Eclipsing Binary Systems: TY Pegasi and X Trianguli

Abstract

ABSTRACTO - C curves of two EA‐type eclipsing binaries, TY Peg and X Tri, are formed and studied in detail based on all available times of light minimum. For TY Peg, it was discovered that the general trend of the O - C curve showed a downward parabolic variation, which indicates a secular period decrease with rate at dP/dt = -1.16 × 10-6 days yr−1. When the secular decrease is removed from the O - C curve, the residuals can be described by several linear ephemerides, suggesting several sudden period jumps. For the other one, X Tri, it is found that the general O - C trend also indicates a secular period decrease (dP/dt = -1.42 × 10-7 days yr−1), and several irregular period jumps are found to superpose on the long‐time period decrease. This kind of period change, irregular sudden jumps superposed on secular decrease, is typical for many other Algol‐type binary systems such as TU Her, UU And, Z Per, Y Psc, BO Mon, FH Ori, RT Per, and TX UMa. The period changes of these systems may be caused by orbital angular momentum loss via variable magnetic coupling and gravity coupling between the components.