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).