TESS photometry of the eclipsing δ Scuti star AI Hydrae

Abstract

Abstract AI Hya has been known as an eclipsing binary with a monoperiodic $\delta$ Sct pulsator. We present the results from its TESS (Transiting Exoplanet Survey Satellite) photometry observed during Sector 7. Including our five minimum epochs, the eclipse timing diagram displays the apsidal motion with a rate of $\dot{\omega } = 0.075 \pm 0.031\:$deg$\:$yr$^{-1}$, which corresponds to an apsidal period of $U = 4800\pm 2000\:$yr. The binary star model represents that the smaller, less massive primary component is $427\:$K hotter than the pulsating secondary, and our distance of $612\pm 36\:$pc is in good agreement with the Gaia distance of $644\pm 26\:$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 $P_{\rm pul}/P_{\rm orb} = 0.012$–0.021 and the pulsation constants of $Q = 0.30$–0.52 d correspond to $\delta$ 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 $\ell = 2$ ($f_1$ and $f_6$).