be seen as objects stronger than 25.5$^m$ in the B band, from 30 to 50 pc respectively.

Consequently, in the vicinity of the Sun we are concerned with the search in the optical for weak blue objects with colors: $U-B\approx~-1.0,~B-V\leq~-0.3,\ {\rm and}~ V-R\approx -0.1$. On the whole sky sphere they can be met with a frequency up to $\approx0.5/{\rm degree^{2}}$, if their temperatures are $\approx
10^{5}\rm~ K$. At the same time in the all–sky survey in the soft X–ray range such sources will be either weak (if $T_{bb}\approx2\cdot10^{5}\rm~ K$) or so weak (at $T_{bb}\approx10^{5}\rm
~K$) that they can be detected only at observations with long exposures in the same frequency band (see Fig.1). The fact that some source was found nevertheless in ROSAT ASS studying 40 small [$\gamma$]{}–ray boxes of a total area of $\approx3.1{\rm \ degree^{2}}$ ( Greiner et al., 1995) does not contradict the above said and this implies that the temperature of such objects is $\la 2\cdot10^{5}\rm \, K$.

Some contribution to the total bolometric luminosity can be made by accretion from interstellar medium onto a single compact object moving at a velocity of [*v*]{} (Bondi & Hoyle, 1944). In the computation of the accretion rate $\dot{M}\sim 