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|This version of the NEXXUS database has been superseded by NEXXUS 2.|
The star catalog is an extract of the Catalogue of Nearby Stars (CNS, version 29 March 2002) containing all stars known within 25 pc to the sun, contributed by H. Jahreiss, Astronomisches Recheninstitut Heidelberg. This sample of stars consists of 3231 stars of which 1075 are contained in 461 binary and 41 multiple systems. Additionally 17 binary stars were handled as one star. The X-ray data were obtained from the final ROSAT Results Archive catalogs. This includes the ROSAT all-sky survey (RASS), i.e. the ROSAT Bright Source and Faint Source Catalog as well as the final versions of the source catalogs from pointed observations, the Second ROSAT Source Catalog of Pointed Observations with the Position Sensitive Proportional Counter with (PSPCF) and without Boron filter (PSPC) and the First ROSAT Source Catalog of Pointed Observations with the High Resolution Imager (HRI) as announced by ROSAT Consortium, ROSAT News No. 74, 2001-Aug-09. The extreme UV data were provided by J. Pye, Department of Physics & Astronomy, University of Leicester, and contain the ROSAT Wide Field Camera (WFC) All-Sky survey and the ROSAT Wide Field Camera Pointed Observations.
The identification of the stars as X-ray or extreme UV sources was done by coordinate match of the position of the star and the source, corrections to the star position by proper motion included. As to the accuracy of the coordinate match, offsets of 120" for RASS, 60" for PSPC and 30" for HRI where accepted. For the XMM data an offset of 30" was accepted. As to the WFC data, a 120" offset was accepted for both the survey and the pointed observations. Note that the star coordinates in the Catalogue of Nearby Stars are not very precisely, although only very few great coordinate offsets appeared. In such cases, and also when the X-ray sources were rather weak, optical and X-ray images according to the sources where visually inspected to verify the identity of star and X-ray source.
This method resulted in 1334 of the 3231 stars to be detected as X-ray sources. In most cases it was not possible to separate the detected binary and multiple systems with RASS, but in pointings sometimes it was. So it occurs that one can find an X-ray source associated with more than one star. Sometimes this resulted in the low precision of the star position as well. The detected X-ray source was therefore attributed to all components. No division of count rate or the resulting X-ray luminosity was made in such cases. As a consequence data for binary and multiple stars has to be watched with care. There are only few cases, for example Sirius and Procyon, where it is known that only one component causes the X-ray emission, the other component was refused here.
When screening the data it has also to be considered that, especially for the survey data, the count rates are mean values for the whole observation time. There was no attempt made to remove flares or variability.