Issue |
Astron. Astrophys. Suppl. Ser.
Volume 128, Number 2, March I 1998
|
|
---|---|---|
Page(s) | 349 - 357 | |
DOI | https://doi.org/10.1051/aas:1998384 | |
Published online | 15 March 1998 |
Searching for old neutron stars with ROSAT
II. Soft X-ray sources in galactic dark clouds
1
Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
2
Palomar Observatory, California Institute of Technology, Pasadena, CA 91125, USA
Received:
16
December
1996
Accepted:
1
August
1997
This is the second in a series of three papers constraining the number of
detectable old neutron stars in the Galaxy.
Here, I present the statistical analysis of a sample of X-ray sources
coincident with areas of dark clouds in the Galactic plane. I compare
this sample with all sources in the ROSAT All-Sky Survey
bright source catalog within of the Galactic plane.
I present the results of an identification program of a subset of
sources that are compatible with a soft, thermal X-ray spectrum
and an effective source temperature of less than 70 eV.
The three brightest sources in this sample form an intriguing subgroup.
One of them is a previously identified candidate for an accreting
neutron star. I identify the other two sources with hot white dwarf
stars. I find no new accreting neutron star candidate in this sample.
Based on this result, I derive an upper limit to the space density of
accreting neutron stars in fields of Galactic dark clouds of
at a count rate
.
Key words: surveys / X-rays: stars / stars: neutron; white dwarfs
© European Southern Observatory (ESO), 1998