Absolute Properties of Two Double-lined Algol-type Binaries with Cyclic Period Changes

Abstract The formation, evolution, and stability of multiple star systems are still open questions in the field of astrophysics. Algol-type binaries are important for obtaining precise physical parameters, investigating the reversal of the mass ratio, and studying the multiplicity of stars. We present a detailed analysis of RW Leo and RT Per with the high-precision time-series radial velocities from the LAMOST-medium-resolution spectroscopic survey and TESS light curves, and we first obtained their absolute parameters. We found that RT Per and RW Leo are post-mass transfer SD2-type semidetached binaries with mass ratios of 0.29 and 0.176, respectively, and the evolved secondary components almost fill their Roche lobe (both ∼99.4%). Moreover, their O − C diagrams show double-cycle oscillations, and the oscillation periods are ∼78 yr and ∼41 yr for RW Leo and ∼247 yr and ∼41 yr for RT Per, respectively. The long-period of them may be caused by the presence of a third body with a mass not less than 0.4 M ⊙ , but we did not detect the third light. For RT Per, our fitting data do not fully cover a complete long-period oscillation (∼247 yr), and longer duration observations are needed to check our results in the future. For the 41 yr oscillations of RW Leo and RT Per, the cyclic magnetic activity from their active secondary components is a probable reason. Besides, after 2451218.604 (HJD), we also discovered that the magnetic activity cycle of RT Per suddenly halved to 20.88 yr because of a possible change in the geometry of the secondary’s magnetic field.