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:
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
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.
For more information please contact:H.-J. Hagen