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Eccentric ellipsoidal variables (aka heartbeat stars) is a class of eccentricbinaries in which proximity effects, tidal distortion due to time-dependenttidal potential in particular, lead to measurable photometric variability closeto the periastron passage. The varying tidal potential may also give rise totidally-excited oscillations (TEOs). TEOs may play an important role in thedynamical evolution of massive eccentric systems. Our study is aimed at thedetection of TEOs and characterisation of the long-term behaviour of theiramplitudes and frequencies in the extreme-amplitude heartbeat star MACHO80.7443.1718, consisting of a blue supergiant and a late O-type massive dwarf.We use two seasons of Transiting Exoplanet Survey Satellite (TESS) observationsof the target to obtain new 30-min cadence photometry by means of thedifference image analysis of TESS full-frame images. In order to extend theanalysis to longer time scales, we supplement the TESS data with 30-years longground-based photometry of the target. We confirm the detection of the known$n=23$, 25, and 41 TEOs and announce the detection of two new TEOs, with $n=24$and 230, in the photometry of MACHO 80.7443.1718. Amplitudes of all TEOs werefound to vary on a time scale of years or months. For $n=25$ TEO amplitude andfrequency changes are related, which may indicate that the main cause of theamplitude drop of this TEO in TESS observations is the change of its frequencyand increase of detuning parameter. The light curve of the $n=230$ TEO isstrongly non-sinusoidal. Its high frequency may indicate that the oscillationis a strange mode. We also find that the orbital period of the system decreasesat the rate of about 11 s(yr)$^{-1}$, which can be explained by a significantmass loss or mass transfer in the system with a possible contribution fromtidal dissipation.

astronomy and astrophysics

Tidally excited oscillations in MACHO 80.7443.1718: Changing amplitudes  and frequencies, high-frequency tidally excited mode, and a decrease in the  orbital period