tokens: energy redistribution, and the absorption lines of these individual elements dominate different regions of the spectrum, the shape of the bright and dark spots on the stellar surface varies with wavelength. Figure 3. Time evolution of the emergent flux from the surface of the star at different rotational phases in a Gaussian passband centred at 1700 Å with a standard deviation of 50 Å (upper panel) and the TESS passband (lower panel). Predicted flux distribution for reference abundances agrees reasonably with the IUE observations (SWP 19761 and LWR 15774) 2 in Fig. 2 . Small differences are most likely caused by missing opacity in model atmospheres. 3.2 Effect of the individual elements The inhomogeneous distribution of flux in most spectral bands, together with stellar rotation, leads to periodic photometric variability of the star. Fig. 4 shows the overall modelled photometric variability of the star, together with the photometric variability computed only taking into account the effect of each individual chemical element separately, to show the contribution of each element to the overall variability of the star. The central wavelengths and half-widths of the filters used in the plots are taken from Prvák et al. ( 2015 ). While the shape of the curves of the individual elements remains roughly the same at all wavelengths, being ‘composed’ in different ratios results in a curve of varying shape. Figure 4. Light curves of φ Phe computed using only the abundance maps of the individual elements (2010 January), along with the overall variability of the star (solid line) in different passbands. The light curves have been shifted vertically to better demonstrate the variability and marked by central wavelengths of the corresponding filters. Note the different vertical scale of the two panels. Fig. 5 shows the dependence of the amplitude of the photometric variability on wavelength. Again, the amplitude of the overall variability, defined as one-half of the difference between the maximum and the minimum magnitude of the star, is plotted together with the amplitude of the variability computed only taking into account the influence of the four chemical elements, one at a time. The variability of the star is largest in the far-UV part of the spectrum, especially around 1300–1400 Å, mainly because of the very low overall flux in this region. In the near-UV and the optical region up to about 6000 Å, the amplitude in narrow passbands varies significantly with wavelength due to the significant absorption in lines. In the red and the infrared, the variability is mostly governed by re-emission in continuum and the amplitude is relatively constant throughout the region. Figure 5. Amplitude of the photometric variability of φ Phe (2010 January) computed as a function of wavelength in Gaussian passbands with a standard deviation of 50 Å. Yttrium, which shows the most pronounced abundance variation, seems to also have the strongest effect on the variability,
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