We have investigated the nature of the magnetic white dwarf LP 790-29 = LHS 2293 by polarimetric monitoring , searching for short-term variability .
No periodicity was found and we can exclude rotation periods between 4 sec and 1.5 hour with a high confidence .
Maximum amplitudes of sinusoidal variations are \Delta R < 0.009 mag and \Delta V _ { R } < 0.7 % for a mean value of the R - band circular polarization of V _ { R } = +9.1 \pm 0.3 % .
Combined with earlier results by other authors , our observation suggests that LP 790-29 is , in fact , an extremely slowly rotating single white dwarf and not an unrecognized fast rotator and/or disguised cataclysmic variable .