Template coadd#

The combination of processed images with the best seeing, for a patch of sky and for each of the six LSST filters, to be used as a template for difference imaging.

Citation: NSF-DOE Vera C. Rubin Observatory (2025); Legacy Survey of Space and Time Data Preview 1: template_coadd dataset type DOI Logo https://doi.org/10.71929/rubin/2570314 [BibTeX]

Access#

The template coadd images are accessible via the Butler, SIA, and TAP services.

Butler#

  • Dataset type: (‘template_coadd’, {band, skymap, tract, patch}, ExposureF)

  • Format: FITS

  • Number of Butler datasets: 2,730

SIA and TAP#

Schema: ObsCore table

IVOA calibration level: 3

Dataproduct subtype: lsst.template_coadd

Description#

For DP1 the one-third of all visit images with the best seeing were used as input images (or the best 12, if there were fewer than 36 images total). A mean stacking algorithm, weighted by inverse variance, combines selected exposures.

Each individual template coadd image covers a single patch of the sky: a quadrilateral sub-region of the overall skymap that covers approximately 79 square arcminutes. Patches slightly overlap at their edges. Template coadd images are for a single filter.

Processing#

The template coadd images are the result of Image coaddition, and they are used in Difference image analysis (DIA).

Pixel data#

The template coadd images have three planes of pixel data.

Image: sky pixel data in flux units of nJy.

Variance: uncertainty (noise) in the flux in units of nJy^2.

Mask: an integer bitmask of representative flag values that indicate processing status or issues, similar to the SDSS bitmasks.

Metadata#

The metadata for template coadd images retrieved from the Butler include a list of the input visit images, and the derived PSF, photometric calibration, and WCS.

WCS#

The World Coordinate System objects for coadd images are exactly representable as FITS (they are simple TAN projections), but each tract has its own WCS that is shared by all patches, with an integer offset that must be applied for each patch manually to index the pixel arrays.

See WCS FITS approximations and misleading interfaces for more information.

Tutorials#

See the 200-level notebook or 200-level portal tutorials demonstrating how to access the template coadd images.