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Hamburger Sternwarte - Research

Hamburg Quasar Survey

The Hamburg Quasar Survey is a wide-angle objective prism survey searching for quasars with B<17.5 on the northern sky. The survey plates have been taken with the former Hamburg Schmidt telescope , which is located at the Spanish-German Astronomical Center (DSAZ) on Calar Alto/Spain since 1980. For the survey we use the 1.7° prism providing unwidened objective prism spectra with a dispersion of 1390 Å/mm at Hgamma. The field size on the 24cm*24cm plates is 5.5°*5.5°, giving a scale of 12 µm/mm on the plate. Under conditions of good seeing the FWHM of the images is 30 µm (plate resolution) giving a spectral resolution of 45Å at Hgamma on the objective-prism plates. Two prism plates are taken per field, and for each field with delta>15° the prism plates are supplemented with unfiltered direct plates to determine accurate positions and to recognize overlaps. For the region 0°<delta<15° the digitized POSS plates from the Digitized Sky Survey are taken.

The plate material is the KODAK IIIa-J emulsion which records spectra between lambda=3400 Å and lambda=5400 Å. Before exposure the plates are hypersensitized in forming gas. Prism plates are exposed typically 50-60 min. in which time the sky background has increased the background photographic density level to 1.0-1.5 (diffuse densities).

The complete northern sky (delta>0°) can be covered by 567 fields, if the Milky Way region (|b|<20°) is omitted. The taking of the plates was completed in 1997. The present coverage of the sky is given in the Figure:

Survey Status

The status of the survey is color-coded, meaning completed fields (dark grey), and fields without direct plate (light grey).

To scan the plates there are three scan modes dubbed ''Low-Resolution-Scan'' (LRS), ''Direct-Plate-Scan'' (DPS) and ''High-Resolution-Scan'' (HRS). The LRS mode is used to scan objective prism plates with a 100 µm slit running perpendicular to the direction of dispersion. The restriction to low resolution spectra allows the digitization of an objective prism plate in less than 3 hours. The spectra of candidate objects, selected from the data base of low resolution spectra, are scanned later in HRS mode with full resolution. The DPS mode is used to scan the direct plates with a 20µm*20µm sized slit in 20 µm (1.7") steps in each direction. Due to the scan technique applied (low-resolution spectra), an additional scan to obtain high-resolution spectra is required.

The export of the digitized database of low-resolution spectra is therefore not planned. Use of the database is however possible in collaboration with Hamburg astronomers. A catalogue of the plates taken in the course of this survey is available, containing the plate centers, observing epochs etc. A description of the catalogue is provided.

Since 1999 we upgrade our scans within the HQS++ project. For each field the best objective prism plate is scanned with full resolution.

Collaborators: D. Engels,  H.-J. Hagen,  D. Reimers, 
For more information please contact:H.-J. Hagen

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