The nature of the photometric variability of HgMn stars: a test of simulated light curves of φ Phe against the TESS data

The inhomogeneous surface distribution of heavy elements is known to cause periodic light variability of magnetic chemically peculiar stars. It is unclear to what extent the same paradigm applies to mercury–manganese (HgMn) stars. We aim to model the photometric variability of the HgMn star φ Phe using abundance maps obtained from high-resolution spectroscopy and to study how this variability evolves with time. We compute a grid of atlas12 model atmospheres and the corresponding synspec synthetic spectra. Interpolating within this grid and integrating the specific intensity over the visible stellar surface at different rotational phases, we obtain theoretical light curves of the star. We predict the variability of φ Phe in the ultraviolet and in the visible spectral regions with amplitude of the order of millimagnitudes, mainly caused by absorption in lines of yttrium, chromium, and titanium. We also show how this variability is affected by changes of the distribution of the heavy elements over time. The main characteristics of the predicted light variability of φ Phe correspond roughly to the variability of the star observed with the Transiting Exoplanet Survey Satellite (TESS).