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A&A Supplement series, Vol. 123, May II 1997, 103-114

Received August 29; accepted September 5, 1996

Identification of a complete sample of northern ROSAT All-Sky Survey X-ray sources

II. The optical observations

F.-J. Zickgrafgiftex2html_wrap_inline2101tex2html_wrap2123tex2html_wrap2125 - I. Thiering tex2html_wrap2127 - J. Krautter tex2html_wrap2129 - I. Appenzeller tex2html_wrap2131 - R. Kneer tex2html_wrap2133 - W.H. Voges tex2html_wrap2135 - B. Ziegler tex2html_wrap2137tex2html_wrap2139 - C. Chavarria tex2html_wrap2141 - A. Serrano tex2html_wrap2143 - R. Mujica tex2html_wrap2145 - M. Pakull tex2html_wrap2147 - J. Heidt tex2html_wrap2149

Send offprint request: F.-J. Zickgraf

tex2html_wrap2151  Landessternwarte Königstuhl (LSW), D-69117 Heidelberg, Germany - Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse, Postfach 1603, D-85740 Garching, Germany
tex2html_wrap2153  Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), A. Postal 51 y 216 Z.P., 72000 Puebla, Mexico
tex2html_wrap2155  Observatoire de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France
tex2html_wrap2157  Universitätssternwarte München, Scheinerstr. 1, D-81679 München, Germany
tex2html_wrap2159  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 tex2html_wrap_inline2103, with tex2html_wrap_inline2105 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, tex2html_wrap_inline2107. In the area near the NGP (low tex2html_wrap_inline2109) "extragalactic'' counterparts dominate, while in the area with the highest tex2html_wrap_inline2111 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

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