Two new magnetic white dwarf accretion binaries with extremely low mass-transfer rates have been discovered in the course of the Sloan Digital Sky Survey .
Measured magnetic fields are 42 MG and 57 MG , and one system orbits with a period of just 82 min .
The new systems therefore significantly expand the range in properties exhibited by the small class .
The measured accretion rates are very low , 0.6 - 5 \times 10 ^ { -13 } ~ { } M _ { \sun } yr ^ { -1 } , and multiple visits spanning more than a year confirm that this is not a short-lived characteristic .
It is becoming increasingly clear that the low- \dot { M } magnetic white dwarf binaries accrete by nearly complete magnetic capture of the stellar wind from the secondary star rather than by Roche lobe overflow .
The accretion rates therefore provide some of the first realistic estimates of the total wind loss rates from M dwarfs .
Although one or more of the eight systems known to date may be interrupted or possibly even extinct Polars , several lines of evidence suggest that most are pre-Polars whose evolution has not yet brought the secondaries into contact with their Roche surfaces .
Considering the difficulties of identifying binaries over a wide range in field strength and accretion rate , it is quite possible that the space density of wind-accreting magnetic binaries exceeds that of the classical X-ray emitting , Roche-lobe overflow Polars .