  Mercury-manganese (HgMn) stars are late-B upper main sequence chemically
peculiar stars distinguished by large overabundances of heavy elements, slow
rotation, and frequent membership in close binary systems. These stars lack
strong magnetic fields typical of magnetic Bp stars but occasionally exhibit
non-uniform surface distributions of chemical elements. The physical origin and
the extent of this spot formation phenomenon remains unknown. Here we use 2-min
cadence light curves of 64 HgMn stars observed by the TESS satellite during the
first two years of its operation to investigate the incidence of rotational
modulation and pulsations among HgMn stars. We found rotational variability
with amplitudes of 0.1-3 mmag in 84 per cent of the targets, indicating
ubiquitous presence of starspots on HgMn-star surfaces. Rotational period
measurements reveal six fast-rotating stars with periods below 1.2 d, including
one ultra-fast rotator (HD 14228) with a 0.34 d period. We also identify
several HgMn stars showing multi-periodic g-mode pulsations, tidally induced
variation and eclipses in binary systems.
