Welcome to NEXXUS 2, the Database for Nearby X-ray and extreme UV emitting Stars. NEXXUS is a catalog of of all known stars within a distance of 25 pc to the Sun that are identified as X-ray and/or extreme UV sources from Einstein, EUVE, ROSAT, and XMM-Newton data based on positional coincidence.
The underlying star catalog is an extract of the NStars Database, containing all stars within 25 pc to the Sun. Additional information has been provided by Ken Slatten or extracted from SIMBAD. The source catalogs from Einstein Imaging Proportional Counter (IPC) and High Resolution Imager (HRI) as incorporated in the CDS have been merged with additional information from the observed fields (CDS catalogs IX/13 and 25, IX/24). All five source lists from the Second EUVE Catalogs (CDS catalogs IX/35), i.e. the All-Sky survey, the Deep Survey of half the ecliptic plane, sources detected in other ways, joint EUVE-ROSAT Detections, and the Right Angle Program (RAP) included. The ROSAT X-ray data were obtained from the final ROSAT Results Archive catalogs, i.e. the ROSAT All-Sky survey (RASS), split into Bright and Faint Source Catalog, 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 ROSAT WFC data (All-Sky survey and pointed observations) were provided by J. Pye, Department of Physics & Astronomy, University of Leicester. The 2XMM Serendipitous EPIC Source Catalog and the XMM Slew Survey EPIC Source Catalog have been downloaded from the XMM-Newton Science Archive (XSA).
Stars have been identified as X-ray or EUV sources by coordinate match, with proper motion corrections included. Note that, especially for the survey catalogs, source coordinates are often not very precise. Sometimes this applies also to stellar coordinates and proper motions. Thus, certain coordinate offsets between star and X-ray/EUV source have been accepted. For the 2XMMp data, the maximum allowed offset was 20", and 80" for the XMM Slew Survey. For the ROSAT data, the required accuracy was set to 120" for RASS, 60" for PSPC(F), and 30" for HRI. A 120" offset was accepted as well for ROSAT WFC data (both the survey and the pointed observations) as for the EUVE detections. Thresholds for Einstein IPC and HRI were set to 100" and 20".
The whole sample consists of 2627 stars, 1217 of them were detected as X-ray/EUV sources. Note however, that in most cases it is not possible to separate binary or multiple systems in the surveys, but sometimes in pointed observations. Thus there are sources associated with more than one star. In such cases the source has been attributed to all components, and no division of the count rate or the resulting X-ray luminosity has been made. As a consequence, data for binary and multiple stars has to be watched with care. There are only few cases, e.g. Sirius and Procyon, where it is known that only one component causes the X-ray emission; if so, the other component was refused. It must also be considered that the count rates are mean values for the whole observation, no attempt was made to remove flares or other kinds of variability.
