A&A Supplement series, Vol. 123, May II 1997, 103-114
Received August 29; accepted September 5, 1996
F.-J. Zickgraf
- I. Thiering 
-
J. Krautter 
-
I. Appenzeller 
- R. Kneer 
- W.H. Voges 
-
B. Ziegler 
- C. Chavarria 
-
A. Serrano 
- R. Mujica 
- M. Pakull 
-
J. Heidt 
Send offprint request: F.-J. Zickgraf
Landessternwarte Königstuhl (LSW), D-69117 Heidelberg, Germany
- Max-Planck-Institut für Extraterrestrische Physik (MPE),
Giessenbachstrasse, Postfach 1603, D-85740 Garching, Germany
Instituto Nacional de Astrofisica, Optica y Electronica (INAOE),
A. Postal 51 y 216 Z.P., 72000 Puebla, Mexico
Observatoire de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg,
France
Universitätssternwarte München, Scheinerstr. 1, D-81679 München,
Germany
Instituto de Astronomia-UNAM, Apdo Postal 70-264, 04510 México
D.F., Mexico
We describe a program for the optical identification of a
representative sample
of RASS sources contained in six study areas north of 
,
with 
including one region near the North
Galactic pole (NGP) and one near the North Ecliptic pole (NEP) and
present some preliminary results.
A full identification has been carried out for a count-rate and area-limited
complete subsample comprising
674 sources. The ratio of "extragalactic'' ( e.g. AGN, clusters of
galaxies) to "stellar''
(e.g. coronal emitters, active binaries) counterparts was found
to depend on the galactic neutral hydrogen column density, 
. In the
area near the NGP (low 
)
"extragalactic'' counterparts dominate, while in
the area with the highest 
most X-ray sources are identified with
stellar counterparts.
keywords: surveys -- X-rays: general -- X-rays: galaxies -- X-rays: stars -- galaxies: active -- galaxies: cluster: general