This article describes the SDSS Legacy Imaging data products hosted at MAST.

On this page...

Summary

The SDSS Legacy Imaging Survey produced wide-field images and ugriz photometry for about 1/3 of the whole sky. Each individual field is a rectangle with a size of 10 by 13 arcminutes on the sky. An example field is shown in Figure 1.

The raw images were processed with the SDSS Imaging Pipeline to produce calibrated fits images and photometric catalogs of imaging parameters. This page lists all of the SDSS Legacy Imaging data products available at MAST. 

Figure 1 - A preview image for SDSS field 5390-6-162. This field contains the globular cluster Messier 53, which is visible on the left side of the field.


Data Products at MAST

The SDSS Legacy Imaging data products available at MAST are listed below. All SDSS Imaging observations in MAST follow the naming scheme:

sdss_image_[RUN]-[CAMCOL]-[FIELD]

where observation names start with the literal string "sdss_image_" and the other parameters are defined as:

  •  [RUN] is the zero-padded identification number for that photometric run: a six-digit number between "000109" and "008162"
  •  [CAMCOL] is the camera column identifying the scanline within the run, an integer between 1-6
  •  [FIELD] is the field number for that observation: the field number typically starts at 11 (after an initial rampup time), and can be as large as 800 for particularly long runs. 

An example SDSS Imaging observation name in MAST would be, "sdss_image_005385_1_0012". Observation names are all lowercase. Each observation represents one SDSS field in one filter target, and contains both fits frame image and the preview jpg files. More documentation for all SDSS Legacy Imaging products can be found on the SDSS webpages describing the Imaging Data Overview and Imaging Basics page.

Frame Images

The full frame images contain the calibrated, sky-subtracted corrected frame plus associated calibration meta-data such as observation date and coordinates. The flux is in units of nanomaggies. For more details on SDSS flux units, see Measures of Flux and Magnitude. 

Preview Images

  • frame-irg-{RUN}-{CAMCOL}-{FIELD}.jpg

The preview files are jpg images created for each field by stacking three filters (i, r, and g) into a an RGB image.

Catalog Files

The SDSS Legacy Imaging survey provides several different catalog products containing various observation information and analysis properties for the SDSS Frames. Refer to the Data Access at MAST page for more information on how to search and download SDSS catalog data at MAST.

The catalog file types hosted at MAST are described below:

photoRunAll

The "photoRunAll" catalog provides a summary of the observing information from the SDSS Legacy Imaging survey. This includes observation dates, coordinates, run identifiers, and reference information for all photometric runs completed during the survey. 

 photoField files

The "photoField" catalog files contain the observing summary information and properties of each field in a camera run. There is one photoField file for each run-camcol, and contains information for all fields in that run. 

 photoObj files 

The "photoObj" catalog files contain files contain the full, calibrated outputs of the SDSS Imaging Pipeline, including information on source detection, source classification (i.e., galaxy, star, or other), magnitude measurements, and quality flags for each field. There is one photoObj file for each run-camcol-field combination, but covers all five filters (ugriz) within that field.