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Optically bright active galactic nuclei in the ROSAT-Faint source catalogue
To build a large, optically bright, X-ray selected AGN sample we havecorrelated the ROSAT-FSC catalogue of X-ray sources with the USNOcatalogue limited to objects brighter than O=16.5 and then with the APSdatabase. Each of the 3212 coincidences was classified using theslitless Hamburg spectra. 493 objects were found to be extended and 2719starlike. Using both the extended objects and the galaxies known frompublished catalogues we built up a sample of 185 galaxies withO_APS<17.0 mag, which are high-probability counterparts of RASS-FSCX-ray sources. 130 galaxies have a redshift from the literature and foranother 34 we obtained new spectra. The fraction of Seyfert galaxies inthis sample is 20%. To select a corresponding sample of 144high-probability counterparts among the starlike sources we searched forvery blue objects in an APS-based color-magnitude diagram. Forty-onewere already known AGN and for another 91 objects we obtained newspectra, yielding 42 new AGN, increasing their number in the sample to83. This confirms that surveys of bright QSOs are still significantlyincomplete. On the other hand we find that, at a flux limit of 0.02count s-1 and at this magnitude, only 40% of all QSOs aredetected by ROSAT.Tables 2, 3 and 4 are only available in electronic form athttp://www.edpsciences.org
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
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