ИСТИНА

We discuss several populations of isolated compact objects, which can be potentially observed by Spectrum-RG. The most promising class of objects is formed by close-by isolated cooling neutron stars. We apply new cooling curves and discuss properties of these sources on the P-Pdot diagram. We demonstrate that eROSITA can increase the number of known sources of this kind by a factor of ~3. New discoveries will be very important to clarify the field decay scenario, and to advance the program for "Grand unification" of neutron stars. Then we discuss isolated cooling young white dwarfs. These objects are also promising targets for eROSITA. Many of them have been observed by ROSAT, and eROSITA will increase the number. Finally, we briefly discuss the possibility to observe magnetars using ART-XC and comment on the long-discussed possibility to detect isolated accreting neutron stars.