TESS Photometry of the Eclipsing $δ$ Scuti Star AI Hydrae

Abstract

AI Hya has been known as an eclipsing binary with a monoperiodic δ Sct pulsator. We present the results from its TESS photometry observed during Sector 7. Including our five minimum epochs, the eclipse timing diagram displays the apsidal motion with a rate of ω = 0.075±0.031 deg year −1 , which corresponds to an apsidal period of U = 4800±2000 years. The binary star model represents that the smaller, less massive primary component is 427 K hotter than the pulsating secondary, and our distance of 612±36 pc is in good agreement with the Gaia distance of 644±26 pc. We subtracted the binary effects from the observed TESS data and applied a multifrequency analysis to these residuals. The result reveals that AI Hya is multiperiodic in its pulsation. Of 14 signals detected, four (f 1 , f 2 , f 3 , f 6 ) may be considered independent pulsation frequencies. The period ratios of P pul /P orb = 0.012−0.021 and the pulsation constants of Q = 0.30−0.52 days correspond to δ Sct pulsations in binaries. We found that the secondary component of AI Hya pulsates in both radial fundamental F modes (f 2 and f 3 ) and non-radial g 1 modes with a low degree of ℓ = 2 (f 1 and f 6 ).