SEARCHING FOR OLD NEUTRON-STARS WITH ROSAT - I - SOFT-X-RAY SOURCES IN MOLECULAR CLOUDS AT HIGH GALACTIC LATITUDE

This is the first in a series of three papers aiming to put strong obs ervational constraints on the number of old accreting neutron stars in the Galaxy. Old neutron stars have been predicted to be visible as so ft X-ray sources. The brightest sources are expected where the density of the interstellar medium is high. I present an X-ray survey of a co mplete sample of molecular clouds at high galactic latitudes based on the ROSAT All-Sky Survey. I detect 89 sources inside the projected con tours of the molecular clouds and report on a comprehensive identifica tion program. For all sources I searched astronomical catalogs and cre ated finding charts. I also observed all sources at radio frequencies, most of them at 1.4 GHz and at 8 GHz. For sources with bright counter parts, optical spectra are presented. For fainter sources, optical CCD images are shown. Of all sources, 54 are securely identified and for the majority of the remaining sources likely identifications are given . I find no candidate for an old accreting neutron star in this sample . From this survey I derive an upper limit to the neutron star density of 50 sr(-1)at a ROSAT count rate of 0.012 s(-1).