Observations of magnetic white dwarfs in the Special Astrophysical Observatory of the Russian Academy of Sciences

Studies of magnetic white dwarfs in the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) have been carried out since 1990 with the 6-m telescope using various spectrographs and with the 1-m Zeiss-1000 telescope using the Multi-Mode Photometer-Polarimeter (MMPP). As a result, we have derived direct estimates of the longitudinal magnetic field obtained with spectropolarimetric observations and circular polarization values in the photometric mode. We observed both well-known magnetic white dwarfs and objects with no data about magnetic field. Among well-known magnetic objects, there were white dwarfs with an extremely strong magnetic field of up to hundreds megagauss and weak magnetic white dwarfs with a field of several tens kilogauss. The use of these data and the data obtained by other authors allowed time series of the observations of these objects to be several decades. Analyzing these time series, we estimated the lower limits of the evolution times of the magnetic fields of white dwarfs.