The SDSS Data Release 1 (DR1)
The DR1 data set is defined by imaging data obtained through July
2001 and the spectroscopic observations of the targets that were
selected from these imaging data. The DR1 paper (Abazajian
et al., AJ, submitted) gives a brief overview of the scope and data
quality of DR1. With this release, we are providing two access
tools. The Data Archive Server
(DAS) includes a set of links to the files produced by the imaging
and spectroscopic pipelines, and it also includes a web form that
allows limited ability to search the database and create catalogs. The
Catalog Archive Server
(CAS) is an SQL database of objects, loaded from the DAS files,
that provides extremely powerful search capabilities for the
construction of catalogs of astronomical objects.
We discovered just before the relase that the outputs of the
imaging pipeline contained a systematic offset between what we call
model magnitudes and Petrosian magnitudes of galaxies. Nevertheless,
the release went ahead because the SDSS Collaboration has published
more than a hundred papers in refereed journals that are based on data
files of the quality now released as DR1 (see the SDSS publication list).
The SDSS Collaboration is eager to let the astronomical community use
the current data because the quality is superb, despite the small set
of parameters that are problematic. In summary, we have validated the
DR1 data with the following primary caveats:
- For photometry of resolved sources, one should use Petrosian
magnitudes, especially at the bright end.
- For photometry of unresolved sources, one should use PSF
magnitudes.
- Colors derived from model magnitudes are almost completely
insensitive to the bug. Model magnitudes remain the optimal
quantities to use for the colors of extended objects, especially at
the faint end.
- The scale sizes derived from the model fits
are systematically wrong. For exponential fits, the effective radii
are systematically too large by 0.15" in the present code
(almost independent of r_e itself), while for the de Vaucouleurs
fits, they are roughly 25% too large (almost independent of r_e
itself, for r_e > 2 arcsec). These correction factors depend
on seeing to some level.
The offset is now understood, and a complete reprocessing of the
data is under way with a new version of the software that provides
reliable model magnitudes. This reprocessing will also take advantage
of improved flat fields. The DR1 data, reprocessed with improved
software and better flat fields, will be part of the next data
release, Data Release 2 (DR2), scheduled for early 2004. This approach
will give the community faster access to a larger set of data
processed with the final version of the pipelines than an intermediate
release of only the DR1 data set.
SDSS is committed to public release of the survey data products.
Formal releases are made as the data are validated by the SDSS
Collaboration. The Early Data
Release (EDR, Stoughton et
al. 2002) published the early SDSS commissioning data. DR1
includes a reprocessing of data in the EDR that pass our data-quality
criteria for the official survey. We recommend that users who
have used the EDR read the description of changes from the
Early Data Release to Data Release 1 (DR1) (see also the DR1 paper
Abazajian et
al. 2003, AJ accepted; astro-ph/0305492).
Last modified: Fri Sep 3 16:05:28 CDT 2004
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