The Kepler spacecraft observed a total of only four AM Herculis cataclysmic variable stars during its lifetime .
We analyze the short-cadence K2 light curve of one of those systems , Tau 4 ( RX J0502.8+1624 ) , which underwent a serendipitous jump from a low-accretion state into a high state during the final days of the observation .
Apart from one brief flare , there was no evidence of accretion during the 70 d of observations of the low state .
As Tau 4 transitioned into a high state , the resumption of accretion was very gradual , taking approximately six days ( \sim 90 binary orbits ) .
We supplement Tau 4 ’ s K2 light curve with time-resolved spectroscopy obtained in both high and low states of accretion .
High-excitation lines , such as He II 468.6 nm , were extraordinarily weak , even when the system was actively accreting .
This strongly suggests the absence of an accretion shock , placing Tau 4 in the bombardment regime predicted for AM Herculis systems with low accretion rates .
In both the high-state and low-state spectra , Zeeman absorption features from the white dwarf ’ s photosphere are present and reveal a surface-averaged field strength of 15 \pm 2 MG .
Remarkably , the high-state spectra also show Zeeman-split emission lines produced in a region with a field strength of 12 \pm 1 MG. Zeeman emission has not been previously reported in an AM Herculis system , and we propose that the phenomenon is caused by a temperature inversion in the WD ’ s atmosphere near the accretion region .