  TESS photometry of the extremely helium-rich hot subdwarfs BD+37 442 and
BD+37 1977 demonstrates multi-periodic low-amplitude variability with principal
periods of 0.56 and 1.14 d, respectively, and with both first and second
harmonics present. The lightcurves are not perfectly regular, implying
additional periodic and/or non-periodic content. Possible causes are examined,
including the binary hypothesis originally introduced to explain X-ray
observations, differentially rotating surface inhomogeneities, and pulsations.
If the principal photometric periods correspond to the rotation periods, the
stars are rotating at approximately 0.7 and 0.3 x breakup, respectively.
Surface Rossby waves (r modes) therefore provide the most likely solution.
