Population type of some X-ray sources.

Twelve X-ray sources from the publications of Bradt et al. (1968), Giacconi et al. (1967 a), and among those the four X-ray sources which are identified with optical objects were selected for a survey on sky photographs. This survey was undertaken to find out, whether X-ray sources are connected with conspicuous features of the interstellar matter. This might be possible considering their general correlation to H U regions found by Braes and Hovenier (1966), and Gursky et al. (1967). The survey showed that there are uniquely shaped H U regions (Schmetterling) within the error circles of the given X-ray positions in four cases: GX 5- 1, GX 13+ 1, GX 17+ 2, and CygX - 1. These peculiar H U regions show sharp, more or less elliptically shaped H U and dark filaments extending from the center of the regions outward. Photometric and/or kinematic distances for these H U regions are known or are derived. In one case, GX 3+ 1, the star which has been identified with the X-ray source, is situated exactly on the outer rim of an elliptically ring-shaped H U filament. Positional chance coincidences for these five cases are considered very unlikely. In two cases, CenX - 2 and ScoX - 1, the stars identffied with these sources also are situated exactly on the outer rim of elliptically ring-shaped dark filaments. In another two cases, GX 9 + 9 and GX 9 + 1, the rims of effiptically ring-shaped dark filaments were found within the errors circles of the X-ray positions. In one case, CygX - 4, the rim of a ring-shaped dark filament is just outside the error box of the X-ray position. Since in those areas of the sky, where the positional coincidences with the ring-shaped dark filaments are found, several dark filaments of this kind are visible, chance coincidences cannot be entirely excluded. A plot of all these objects on the galactic plane (Fig. 3) shows that they are distributed along the spiral arms. If the positional coincidences between some of the X-ray sources and the ring-shaped clouds are real and represent real physical correlations it might be concluded that these X-ray sources are, as X-ray sources, not older than a few 100 years, since the lifetime of regularly ringshaped clouds will not be more than this. Key words: X.rays - stellar evolution - galactic structure