Photometric study of semi-detached eclipsing binary TW Cas based on TESS photometry

Abstract

TW Cas is an eclipsing binary that contains B-type and solar-like components with an orbital period of 1.42832665 d and mass ratio of 0.4873. The semi-detached configuration makes it a key goal for understanding Algol-type eclipsing binaries evolution. However, the physical parameters and evolutionary state of TW Cas are still unknown. W–D differential correction program was employed to give orbital parameters and configuration and extend our knowledge of TW Cas evolution. We present light curves and 64 eclipsing times observed by Transiting Exoplanet Survey Satellite (TESS) telescope. Photometric analyses of the TESS light curve suggest that TW Cas is a semi-detached system where the less massive component is filling its critical Roche lobe, and a large dark spot is found on the polar of the less massive one. By using all light minima times, it is detected that the O−C curve shows an upward parabolic change while a cyclic oscillation is superimposed with an amplitude of 0.024585 days and a period of 113.41 yr. The upward parabolic change may indicate a long-term increase of the orbital period at a rate of 1.41 ×10−7 days yr−1, which reveals a rapid mass transfer between the components. The cyclic oscillation might result from the light-travel-time effect owing to the presence of a third body. The semi-detached configuration that less mass component fills its Roche lobe, together with the long-term increase of orbital period and the presence of a large dark spot on the less massive component indicates that TW Ca is at a critical stage of evolution after a mass ratio inversion.