Flag usage guidance

Table-specific guidance on which flags to apply for typical science-quality selections. It is up to the user to adapt this guidance to their specific science applications.

Object table

Guidance for the application of flags on the deep coadd measurements of static sky objects.

Multi-band requirements: when requiring detections in multiple bands, ensure flux measurements and key pixel flags are valid in each band used. Check pixelFlags_nodata to confirm coverage.

Band-specific flags: The Object table has approximately 100 flags per band. The naming pattern is {band}_{measurement}_flag (e.g., g_psfFlux_flag, i_cModel_flag). Apply the same flag logic to each band independently.

In the code snippets below, f is the filter (ugrizy).

WHERE f_psfFlux_flag = 0                  -- PSF flux succeeded
  AND f_pixelFlags_saturatedCenter = 0     -- No saturation at center
  AND f_pixelFlags_crCenter = 0            -- No cosmic ray at center
  AND f_pixelFlags_interpolatedCenter = 0  -- No interpolation at center
  AND f_pixelFlags_sensor_edgeCenter = 0   -- Not on detector edge
  AND f_invalidPsfFlag = 0                 -- Valid PSF model

Galaxy samples

AND f_cModel_flag = 0        -- CModel fit succeeded
AND f_extendedness = 1       -- Extended source (galaxy)
AND f_extendedness_flag = 0  -- Classification valid

Note

The extendedness classifier has not been fully characterized for purity or completeness. There is currently no published guidance on the selection function these cuts produce. Users should treat galaxy/star separation as approximate and validate against their specific science requirements.

Star samples

AND f_extendedness = 0       -- Point source (star)
AND f_extendedness_flag = 0  -- Classification valid

Note

The same caveats about the extendedness classifier apply as for galaxy samples above.

Stars used and reserved in PSF modeling can also be identified using {band}_calib_psf_used and {band}_calib_psf_reserved in the Source table (see Calibration flags).

High-precision Kron photometry

AND f_kronFlux_flag = 0  -- Kron flux succeeded

High-precision shape measurements

AND f_hsmShapeRegauss_flag = 0  -- HSM shapes succeeded

Strict pixel quality

This is optional.

AND f_pixelFlags_interpolated = 0  -- No interpolated pixels in footprint

Source table

Guidance for the application of flags on single-epoch visit detections.

WHERE centroid_flag = 0               -- Centroid succeeded
  AND psfFlux_flag = 0                -- PSF flux succeeded
  AND pixelFlags_edge = 0             -- Not on CCD edge
  AND pixelFlags_saturatedCenter = 0  -- No saturation at center
  AND pixelFlags_bad = 0              -- No bad pixels

Additional quality filters.

AND pixelFlags_crCenter = 0            -- No cosmic ray at center
AND pixelFlags_interpolatedCenter = 0  -- No interpolation at center
AND pixelFlags_suspectCenter = 0       -- No suspect pixels at center

Calibration stars

If specifically selecting or excluding calibration stars, use calib_* flags (including calib_psf_used and calib_psf_reserved).

ForcedSource table

Guidance for the application of flags on forced photometry at Object positions.

When constructing light curves, apply these flags to each measurement (row) individually. This filters out poor-quality epochs while retaining good measurements for the same object across other visits.

Science-image flux

WHERE psfFlux_flag = 0                -- PSF flux succeeded
  AND pixelFlags_saturatedCenter = 0  -- No saturation at forced position
  AND pixelFlags_edge = 0             -- Position not on edge
  AND invalidPsfFlag = 0              -- PSF model valid

Difference-image flux

AND psfDiffFlux_flag = 0              -- Difference flux succeeded
AND diff_PixelFlags_nodataCenter = 0  -- Difference image has coverage

DiaSource table

Guidance for the application of flags on transient/variable detections on difference images.

High-confidence real astrophysical transients.

WHERE isDipole = 0                    -- Not a subtraction dipole artifact
  AND psfFlux_flag = 0                -- Difference flux succeeded
  AND pixelFlags_edge = 0             -- Not on edge
  AND pixelFlags_saturatedCenter = 0  -- No saturation
  AND pixelFlags_bad = 0              -- No bad pixels

Additional quality filters.

AND centroid_flag = 0  -- Position reliable
AND pixelFlags_cr = 0  -- Not a cosmic ray residual

ForcedSourceOnDiaObject table

Guidance for the application of flags on forced photometry at DiaObject positions.

When constructing light curves, apply these flags to each measurement (row) individually. This filters out poor-quality epochs while retaining good measurements for the same object across other visits.

Difference-image flux

WHERE psfDiffFlux_flag = 0              -- Difference flux succeeded
  AND diff_PixelFlags_nodataCenter = 0  -- Difference image has coverage
  AND pixelFlags_saturatedCenter = 0    -- No saturation
  AND invalidPsfFlag = 0                -- PSF valid

Science-image flux

WHERE psfFlux_flag = 0                  -- Science image flux succeeded
  AND pixelFlags_bad = 0                -- No bad pixels
  AND pixelFlags_saturatedCenter = 0    -- No saturation
  AND invalidPsfFlag = 0                -- PSF valid