A&A Supplement series, Vol. 128, March I 1998, 331-348
Received December 16, 1996; accepted August 1, 1997
R. Danner
This is the first in a series of three papers aiming to put strong
observational constraints on the number of old accreting neutron stars
in the Galaxy. Old neutron stars have been predicted to be visible as
soft 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 complete sample of molecular clouds at high galactic
latitudes based on the ROSAT All-Sky Survey. I detect 89 sources
inside the projected contours of the molecular clouds and report on a
comprehensive identification program. For all sources I searched
astronomical catalogs and created finding charts. I also observed all
sources at radio frequencies, most of them at 1.4GHz and at 8GHz.
For sources with bright counterparts, 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 at a
ROSAT count rate of
.
keywords: surveys -- stars: neutron; white dwarfs -- X-rays: stars -- radio continuum: stars