The Catalog Archive Server - An Introduction

The Catalog Archive Server (CAS) provides access to the object catalogs and related data from the Sloan Digital Sky Survey (SDSS). It is a companion to the Data Archive Server (DAS), which allows users to download images and spectra from the survey.

The CAS uses a Microsoft SQL Server database to store and serve the data. Users can access this data by a number of methods.

1. The SkyServer. This provides a variety of methods to retrieve data:
   1. Radial search. Allows entry of a central coordinate, radius, and constraints on the five simplified magnitudes (ugriz). This query returns ONLY the object coordinates, type. simplified mags with errors, and the object id, as well as the quantities necessary to get data from the DAS (run/rerun/camcol/ field/obj).
   2. Rectangular Search.Identical to the radial search, except that the user specifies a minimum and maximum RA and Dec.
   3. SQL web form. Users can enter Structured Query Language (SQL) queries in a form, and the query will be executed. The query is limited in duration to ? hours, or ??? rows. This query type allows selection of various attributes, combined photometric and spectroscopic queries, and the application of complex constraints. Users new to SQL will want to read our SQL help and the description of the data model and the parameters stored in the various tables.
   4. CrossID. Users input or upload a list of object names and coordinates, and get the nearest oject or objects in the SDSS database for each input object. The match radius is adjustable up to three arcminutes, and users can choose the quantities they want output for each match. The input list is limited to 1000 objects and the output to 10000 objects.
   5. SpecList. This page performs dynamic cross identifications of the SDSS spectroscopic objects with a user defined list of (plate, mjd, fiber) values. In order to avoid congestion on the server, the list is limited to 1000 objects, and to a size of 80KB.
   In addition, the SkyServer provides a tool called the Schema Browser, with which users can browse the various tables, views, and functions available for SQL queries, as well as the different columns available in each. All of the SkyServer interfaces allow data to be returned in HTML, XML, or CSV (comma separated variable) format.
2. The SDSS Query Analyzer (sdssQA). This is a fully self-contained, downloadable Java application which allows submission of SQL queries to the database. It also includes a version of the Schema Browser, and a variety of example queries. With the sdssQA you can open multiple database connections, run multiple queries, and save the output to files on your local disk. Users wishing to run complex SQL queries will want to use this tool. The sdssQA can be downloaded from this page. Documentation on using the sdssQA is also available. Users should read our SQL help and the descriptions of the data model and the parameters stored in the various tables.
3. Emacs interface. This interface, developed by Robert Lupton, which can be downloaded here. Robert has provided some example queries, and there is additional documentation available for this tool. Our SQL help and the descriptions of the data model and the parameters stored in the various tables. are also applicable.
4. sqlcl command line interface. A straightforward command line interface written in Python by Tamas Budavari. The tool can be downloaded, and some help found, on the sqlcl page.

In addition to these database access tools, we have developed some simple interfaces to retrieve color JPG images for lists of objects, with optional overlays of catalog data, finding charts, and a navigation tool that allows you to move around a sky region in a MapQuest-like fashion:

1. Finding Chart. Returns a single JPEG image centered on (ra,dec). This tool allows scaling of the output image, and a variety of overlays are available.
2. Cutout Service. Users can upload a list of up to 1000 objects, and have small JPEG image cutouts for each object displayed, 100 to a page. A variety of overlays are available.
3. Navigator. Displays a JPEG of an area of the sky, and allows the user to zoom and pan. A variety of overlays are available.
4. Object Explorer. Enables you to find individual objects, either based upon their object IDs, or their sky position. The page presents a concise summary of all relevant information about the object, and provides links to all the additional information, like neighbors, fields, the spectroscopic object, spectral plates, cross-identifications in other surveys, or photometric redshifts of galaxies. We also provide links to the low-level data available as binary FITS tables. These include the corrected frames, bit-masks, binned sky, the atlas images and the spectra.