Updated modelling of the oscillating eclipsing binary system AS Eri

We present the results of a recent study of the Algol-type eclipsing binary system AS Eri based on the combination of the MOST and TESS light curves as well as a collection of very precise radial velocities obtained with the spectrographs HERMES operating at the Mercator telescope, La Palma, and TCES operating at the A. Jensch telescope, Tautenburg. The primary component is a known A3 V-type pulsating, mass-accreting star. We fitted the light and radial velocity data with the package PHOEBE, and determined the best-fitting model adopting the configuration of a semi-detached system. We used the orbital period of 2.6641496 \pm 0.0000001 days obtained from an updated (O-C) analysis and the phase gap between the MOST and TESS light curves. The absence of any cyclic variation in the (O-C) residuals confirms the long-term stability of this period. We obtained the absolute component parameters: L1 = 14.125 \pm 0.008 Lsol, M1 = 2.014 \pm 0.004 Msol, R1 = 1.733 \pm 0.006 Rsol, log g1 = 4.264 \pm 0.005 and L2 = 4.345 \pm 0.003 Lsol, M2 = 0.211 \pm 0.001 Msol, R2 = 2.19 \pm 0.01 Rsol, log g2 = 3.078 \pm 0.003 with Teff,2/Teff,1 = 0.662 \pm 0.002. Although the orbital period appears to be stable on the long term and the final solution shows residuals within expected limits, we show that the models derived for each light curve separately entail small differences, e.g. in the temperature of the companion, allowing us to conclude that the light curve is affected by a years-long modulation. We believe that this is caused by the magnetic activity of the cool companion.