The SDSS telescope has a 3º diameter field of view
and imaging is obtained using a drift
scan camera with 30 2048 x 2048 CCDs at the focal plane, and five broad
ugriz, that cover a range from 3000 to 10,000Å. Each continuous
scan constitutes an imaging run and generates a strip; two
strips create a 2.5º wide imaging stripe.
SDSS DR7 Sky Coverage for details.)
A table of SEGUE stripes can be found at
Low Latitude Imaging
Many of these stripes go to quite low Galactic latitude, and some
cross the Galactic plane. The photometric pipeline is not optimized
for the crowded fields found at low latitude, and so caution must be used
in these regions of high stellar density:
- Outputs of the photometric pipeline appear to be good until
the density of objects exceeds ~ 4000 per 10' x 13' field (roughly
ten times the number density of objects at high latitudes).
- The point spread function (PSF) cannot be measured accurately in crowded
fields (the pipeline has difficulty finding suitable isolated stars).
This limits the accuracy of brightness measurements in these fields.
- The pipeline attempts to deblend objects with overlapping
images, but the deblend algorithm fails when the number of overlapping
objects in a single family is too large. In such cases the number of detected
objects reported by the pipeline can be a dramatic underestimate.
SEGUE imaging data is processed using the SDSS photometric pipeline.
Details can be found on the DR7
algorithms web page.
Proper motions are
estimated from comparison with USNO-B data, following the prescription of
Munn et al. (AJ 127, 2004).
These proper motions are utilized in selecting candidates for
certain categories of the
SEGUE target selection algorithm.