We report the detection of Zeeman-split { Ly \alpha } absorption \pi and \sigma ^ { + } lines in the far-ultraviolet Hubble Space Telescope /Space Telescope Imaging Spectrograph spectrum of the magnetic cataclysmic variable RX J1554.2+2721 .
Fitting the STIS data with magnetic white dwarf model spectra , we derive a field strength of B \simeq 144 MG and an effective temperature of 17 000 \mathrm { K } \lesssim \mbox { $T _ { eff } $ } \lesssim 23 000 K. This measurement makes RX J1554.2+2721 only the third cataclysmic variable containing a white dwarf with a field exceeding 100 MG .
Similar to the other high-field polar AR UMa , RX J1554.2+2721 is often found in a state of feeble mass transfer , which suggests that a considerable number of high-field polars may still remain undiscovered .