Vitaly Aitov

Cool (old) white dwarfs with strong large-scale magnetic fields (MWDs) demonstrate, on average, significantly higher field strengths and frequency of occurrence than hot (young) MWDs, despite the fact that the magnetic fields and abundance of such stars should, theoretically, decrease over time. In a series of previous papers we proposed an explanation for this effect by the gradual slowdown of the thermal evolution of MWDs due to magnetically induced suppression of their surface convection. Our modeling showed that this mechanism can explain the increase in the occurrence of extremely cool MWDs. Meanwhile, observations reveal an increasing number of MWDs among significantly younger stars of this class. In this work, we revisit this problem. Unlike previous models, where the birth probability of MWD progenitor stars was considered independent of the age of the Galaxy, we account for the decreasing probability of occurrence of strongly magnetic stars (MWD progenitors) with the age of the Galaxy. Introducing this parameter allowed us to describe the increase in the occurrence of MWDs. This result argues that the population of massive MWD progenitor stars decreases with the age of the Galaxy, apparently due to the weakening of its magnetic properties in the process of evolution.

We studied the magnetic field of chemically peculiar stars in the young Orion OB1 association and in other five older clusters. We have found new evidence of the validity of the relic origin of the magnetic field. In the Orion OB1 association, the magnetic field values and the occurrence frequency of magnetic stars are systematically higher than in older groups. There is no magnetic field generation during the life of a star on the main sequence. The observations were carried out using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We studied the magnetic field of about 80 stars. More than 1000 spectra were obtained with the circular polarization analyzer on the BTA Main Stellar Spectrograph.

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.