DR11 bitmasks

This page details the meaning of the bitmasks provided with Data Release 11 of the Legacy Surveys. The bits are enumerated as a power (i.e. 7 written in a column of bits means two-to-the-power-of-7).

MASKBITS

These definitions apply to both the values in the coadd/*/*/*maskbits* files and to MASKBITS columns in the Tractor and sweeps catalogs. See also the legacypipe bitmask definitions.

Bit

Name

Description

0

NPRIMARY

touches a pixel that is outside the BRICK_PRIMARY region of a brick

1

BRIGHT

touches a pixel within half of the locus of a radius-magnitude relation. Set for Tycho sources with MAG_VT < 13 and Gaia stars with G < 13

2

SATUR_G

touches a pixel that was saturated in at least one \(g\)-band image

3

SATUR_R

touches a pixel that was saturated in at least one \(r\)-band image

4

SATUR_Z

touches a pixel that was saturated in at least one \(z\)-band image

5

ALLMASK_G

touches a pixel that has any of the ALLMASK_G bits set

6

ALLMASK_R

touches a pixel that has any of the ALLMASK_R bits set

7

ALLMASK_Z

touches a pixel that has any of the ALLMASK_Z bits set

8

WISEM1

touches a pixel in a WISEMASK_W1 bright star mask

9

WISEM2

touches a pixel in a WISEMASK_W2 bright star mask

10

BAILOUT

touches a pixel in a blob where we "bailed out" of source fitting

11

MEDIUM

touches a pixel within the locus of a radius-magnitude relation. Set for Gaia stars with G < 16. The MEDIUM radius is twice the BRIGHT radius at the same magnitude

12

GALAXY

touches a pixel in an SGA large galaxy

13

CLUSTER

touches a pixel in a globular cluster

14

SATUR_I

touches a pixel that was saturated in at least one \(i\)-band image (always zero prior to DR10)

15

ALLMASK_I

touches a pixel that has any of the ALLMASK_I bits set (always zero prior to DR10)

16

SUB_BLOB

source is in a large blob that was split into smaller blobs for processing

17

RESOLVED

source lies within a local dwarf galaxy whose stars are resolved (always zero prior to DR11)

18

MCLOUDS

source lies within one of the Magellanic clouds (always zero prior to DR11)

19

WISE_GAIA

source lies in a high-density brick and only includes WISE forced performed on Gaia sources (always zero prior to DR11)

FITBITS

A bit-mask detailing any peculiarities regarding how a source was fit. See also the legacypipe bitmask definitions and the issue that prompted the development of FITBITS.

Bit

Name

Description

0

FORCED_POINTSOURCE

the source was forced to be type PSF

1

FIT_BACKGROUND

the source had its background levels independently fit

2

HIT_RADIUS_LIMIT

the source hit the radius limit during fitting (based on the limits for galaxy models in the Tractor code)

3

HIT_SERSIC_LIMIT

the source hit the Sersic index limit during fitting (e.g., see the Sersic model limits in the Tractor code)

4

FROZEN

the source was not fit (all parameters for the source were frozen at the reference catalog values)

5

BRIGHT

the source is a bright star (see also MASKBITS, above)

6

MEDIUM

the source is a medium-bright star (see also MASKBITS, above)

7

GAIA

the source is a Gaia source

8

TYCHO2

the source is a Tycho-2 star

9

LARGEGALAXY

the source is an SGA large galaxy

10

WALKER

fitting the source shifted its position by > 1 arcsec

11

RUNNER

fitting the source shifted its position by > 2.5 arcsec

12

GAIA_POINTSOURCE

the source was a Gaia source that was treated as a point source

13

ITERATIVE

the source was found during iterative detection

ALLMASK_X/ANYMASK_X

ANYMASK_X denotes a source that touches a bad pixel in any of a set of overlapping X-band images whereas ALLMASK_X denotes a source that touches a bad pixel in all of a set of overlapping X-band images. See, also, the legacypipe bitmask definitions. The ANYMASK and ALLMASK bit masks are defined as follows, mostly from the CP (NOIRLab Community Pipeline).

Bit

Name

Description

0

BADPIX

bad columns, hot pixels, etc.

1

SATUR

saturated

2

INTERP

interpolated

4

CR

single exposure cosmic ray

6

BLEED

bleed trail

7

TRANS

multi-exposure transient

8

EDGE

edge pixel

9

EDGE2

edge pixel

11

OUTLIER

marked as touching an outlier pixel by legacypipe itself

WISEMASK_W1/WISEMASK_W2

WISEMASK_W1 and WISEMASK_W2 have identical bit definitions, the only difference is that WISEMASK_W1 applies to masking in the W1 band and WISEMASK_W2 to masking in the W2 band.

Bit

Name

Description

0

BRIGHT

Bright star core and wings

1

SPIKE

PSF-based diffraction spike

2

GHOST

Optical ghost

3

LATENT

First latent

4

LATENT2

Second latent image

5

HALO

AllWISE-like circular halo

6

SATUR

Bright star saturation

7

SPIKE2

Geometric diffraction spike

Aaron Meisner's unWISE documentation details how these masks were derived.

CCD_CUTS

The survey CCDs files include a bitmask ccd_cuts that is used by the legacypipe code to discard CCDs that have low-quality observations before processing imaging for the Legacy Surveys. Any observations with non-zero vales of ccd_cuts are discarded prior to processing.

In this table, the column names are as they appear in, e.g., the survey CCDs file. The overall zero-points (zpt0) are:

  • \(g, r\) = [25.74, 25.52] for 90Prime (BASS)

  • \(z\) = 26.20 for Mosaic-3 (MzLS)

  • \(g, r, z\) = [25.08, 25.29, 24.92] for DECam (DECaLS)

Bit

Name

Description

0

ERR_LEGACYZPTS

Some error from the legacyzpts code (e.g., the CP had a WCS error, usually due to being very shallow)

1

NOT_GRIZ

Not a \(g\)-, \(r\)-, \(i\)- or \(z\)-band observation

2

NOT_THIRD_PIX

Mosaic-3 one-third-pixel interpolation problem

3

EXPTIME

Exposure time < 30 seconds

4

CCDNMATCH

Number of matching CCDs < 20

5

ZPT_DIFF_AVG

Zeropoint for CCD is different than the average for the exposure: abs(ccdzpt - zpt) > 0.25 for DECam, 0.1 for 90Prime, 0.1 for Mosaic-3

6

ZPT_SMALL

Zeropoint is too low: zpt < (zpt0 - P) where P is [0.5, 0.5, 1.0] mag for [DECam, 90Prime, Mosaic-3]

7

ZPT_LARGE

Zeropoint is too high: zpt > (zpt0 + Q) where Q is [0.25, 0.18, 0.8] mag for [DECam, 90Prime, Mosaic-3]

8

SKY_IS_BRIGHT

Sky is too high; ccdskycounts is more than [90, 150, 180] for DECam [\(g, r, z\)]; [200] for Mosaic-3 [\(z\)] (no cuts are made for 90Prime)

9

BADEXP_FILE

Exposure is listed in the bad_expid.txt file (90prime-bad_expid.txt, mosaic-bad_expid.txt or decam-bad_expid.txt)

10

PHRMS

Photometric calibration RMS is too large: ccdphrms > 0.2

11

RADECRMS

Astrometric calibration RMS is too large: rms (\(\sqrt(\mathtt{ccdrarms^2 + ccddecrms^2})\) > 0.4 arcsec for DECam; 0.2 arcsec for 90Prime; 0.1 arcsec for Mosaic-3

12

SEEING_BAD

Bad seeing measure: (seeing < 0 arcsec OR seeing > 3.0 arcsec), where, e.g., seeing = fwhm \(\times\) 0.262 for DECam

13

EARLY_DECAM

Defined as MJD < 56516 (note that DR8 started with MJD < 56730)

14

DEPTH_CUT

Depth cut code (this is run after the other cuts)

15

TOO_MANY_BAD_CCDS

Remove full exposures if more than 70% of the CCDs are cut

16

FLAGGED_IN_DES

Flagged as bad in DES

17

PHRMS_S7

A special bit for the DECam S7 chip, indicating that an extra cut on ccdphrms (see, e.g., the survey CCDs file) of > 0.1 mag was included

18

DEPTH_CUT_2

An additional depth cut was applied to allow this field to run to completion (likely because a particularly high source density made extractions intractable)

19

PLVER

A bit signifying whether a particular pipeline version should be included

Some of the exact values used to create the CCD_CUTS bitmask are recorded in the legacyzpts code for DECam (and also for the Mosaic-3 and 90Prime cameras).