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Astron. Astrophys. 329, 495-503 (1998)

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The ROSAT deep survey

II. Optical identification, photometry and spectra of X-ray sources
in the Lockman field

M. Schmidt 1, G. Hasinger 2, J. Gunn 3, D. Schneider 4, R. Burg 5, R. Giacconi 6, I. Lehmann 2, J. MacKenty 7, J. Trümper 8 and G. Zamorani 9, 10

1 California Institute of Technology, Pasadena, CA 91125, USA
2 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
3 Princeton University Observatory, Princeton, NJ 08540, USA
4 Pennsylvania State University, University Park, PA 16802, USA
5 Johns Hopkins University, Baltimore, MD 21218, USA
6 European Southern Observatory, Karl-Schwarzschild-Str. 1, D-85748 Garching bei München, Germany
7 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
8 Max-Planck-Institut für extraterrestrische Physik, Karl-Schwarzschild-Str. 2, D-85740 Garching bei München, Germany
9 Osservatorio Astronomico, Via Zamboni 33, I-40126 Bologna, Italy
10 Istituto di Radioastronomia del CNR, via Gobetti 101, I-40129, Bologna, Italy

Received 12 May 1997 / Accepted 11 September 1997


The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the [FORMULA] keV band larger than 5.5 [FORMULA] erg cm-2 s-1 in the Lockman field (Hasinger et al., Paper I). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux.

Key words: surveys – galaxies: active – quasars: emission lines – galaxies: Seyfert – X-rays: galaxies

Send offprint requests to: G. Hasinger

SIMBAD Objects


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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997