Name 
Type 
Units 
Description 

BRICKID 
int32 
Brick ID [1,662174] 

BRICKNAME 
char 
Name of brick, encoding the brick sky position 

OBJID 
int64 
Catalog object number within this brick; a unique identifier hash is BRICKID,OBJID; OBJID spans [0,N1] and is contiguously enumerated within each brick 

BRICK_PRIMARY 
char 
"T" if the object is within the brick boundary 

BLOB 
int64 
Blend family; objects with the same [BRICKID,BLOB] identifier were modeled (deblended) together; contiguously numbered from 0 

TYPE 
char 
Morphological model: PSF=stellar, EXP=exponential, DEV=deVauc, COMP=composite 

RA 
float64 
deg 
Right ascension at equinox J2000 
RA_IVAR 
float32 
1/deg² 
Inverse variance of RA, excluding astrometric calibration errors 
DEC 
float64 
deg 
Declination at equinox J2000 
DEC_IVAR 
float32 
1/deg² 
Inverse variance of DEC (no cos term!), excluding astrometric calibration errors 
BX 
float32 
pix 
X position (0indexed) of coordinates in brick image stack 
BY 
float32 
pix 
Y position (0indexed) of coordinates in brick image stack 
BX0 
float32 
pix 
Initialized X position (0indexed) of coordinates in brick image stack 
BY0 
float32 
pix 
Initialized Y position (0indexed) of coordinates in brick image stack 
LEFT_BLOB 
char 
"T" if an object center has been optimized to be outside the fitting pixel area; otherwise "F" 

DECAM_FLUX 
float32[6] 
nanomaggy 
DECam model flux in ugrizY 
DECAM_FLUX_IVAR 
float32[6] 
1/nanomaggy² 
Inverse variance oF DECAM_FLUX 
DECAM_APFLUX 
float32[8,6] 
nanomaggy 
DECam aperture fluxes on the coadded images in apertures of radius [0.5,0.75,1.0,1.5,2.0,3.5,5.0,7.0] arcsec in ugrizY 
DECAM_APFLUX_RESID 
float32[8,6] 
nanomaggy 
DECam aperture fluxes on the coadded residual images 
DECAM_APFLUX_IVAR 
float32[8,6] 
1/nanomaggy² 
Inverse variance oF DECAM_APFLUX 
DECAM_MW_TRANSMISSION 
float32[6] 
Galactic transmission in ugrizY filters in linear units [0,1] 

DECAM_NOBS 
int32[6] 
Number of images that contribute to the central pixel in each filter for this object (not profileweighted) 

DECAM_RCHI2 
float32[6] 
Profileweighted χ² of model fit normalized by the number of pixels 

DECAM_FRACFLUX 
float32[6] 
Profileweight fraction of the flux from other sources divided by the total flux (typically [0,1]) 

DECAM_FRACMASKED 
float32[6] 
Profileweighted fraction of pixels masked from all observations of this object, strictly between [0,1] 

DECAM_FRACIN 
float32[6] 
Fraction of a source's flux within the blob, near unity for real sources 

OUT_OF_BOUNDS 
bool[6] 
"T" for objects whose center is on the brick; less strong of a cut than BRICK_PRIMARY 

DECAM_ANYMASK 
int32[6] 
Bitwise mask set if the central pixel from any image satisfy each condition 

DECAM_ALLMASK 
int32[6] 
Bitwise mask set if the central pixel from all images satisfy each condition 

WISE_FLUX 
float32[4] 
nanomaggy 
WISE model flux in W1,W2,W3,W4 
WISE_FLUX_IVAR 
float32[4] 
1/nanomaggy² 
Inverse variance of WISE_FLUX 
WISE_MW_TRANSMISSION 
float32[4] 
Galactic transmission in W1,W2,W3,W4 filters in linear units [0,1] 

WISE_NOBS 
int32[4] 
Number of images that contribute to the central pixel in each filter for this object (not profileweighted) 

WISE_FRACFLUX 
float32[4] 
Profileweight fraction of the flux from other sources divided by the total flux (typically [0,1]) 

WISE_RCHI2 
float32[4] 
Profileweighted χ² of model fit normalized by the number of pixels 

DCHISQ 
float32[4] 
Difference in χ² between successfully morecomplex model fits 

FRACDEV 
float32 
Fraction of model in deVauc [0,1] 

FRACDEV_IVAR 
float32 
Inverse variance of FRACDEV 

SHAPEEXP_R 
float32 
arcsec 
Halflight radius of exponential model (>0) 
SHAPEEXP_R_IVAR 
float32 
1/arcsec² 
Inverse variance of R_EXP 
SHAPEEXP_E1 
float32 
Ellipticity component 1 

SHAPEEXP_E1_IVAR 
float32 
Inverse variance of SHAPEEXP_E1 

SHAPEEXP_E2 
float32 
Ellipticity component 2 

SHAPEEXP_E2_IVAR 
float32 
Inverse variance of SHAPEEXP_E2 

SHAPEDEV_R 
float32 
arcsec 
Halflight radius of deVaucouleurs model (>0) 
SHAPEDEV_R_IVAR 
float32 
1/arcsec² 
Inverse variance of R_DEV 
SHAPEDEV_E1 
float32 
Ellipticity component 1 

SHAPEDEV_E1_IVAR 
float32 
Inverse variance of SHAPEDEV_E1 

SHAPEDEV_E2 
float32 
Ellipticity component 2 

SHAPEDEV_E2_IVAR 
float32 
Inverse variance of SHAPEDEV_E2 

EBV 
float32 
mag 
Galactic extinction E(BV) reddening from SFD98, used to compute DECAM_MW_TRANSMISSION and WISE_MW_TRANSMISSION 
Mask Values
The DECAM_ANYMASK and DECAM_ALLMASK bit masks are defined as follows from the CP Data Quality bits.
Bit 
Value 
Name 
Description 

0 
1 
detector bad pixel/no data 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
1 
2 
saturated 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
2 
4 
interpolated 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
4 
16 
single exposure cosmic ray 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
6 
64 
bleed trail 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
7 
128 
multiexposure transient 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
8 
256 
edge 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
9 
512 
edge2 
detailed at https://legacy.noirlab.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html 
GoodnessofFits
The DCHISQ values represent the penalized χ² of all the pixels compared to various models. This 4element vector contains the χ² difference between the bestfit point source, deVauc model, exponential model, and a composite model. The number of degrees of freedom to include as a penalty to these χ² values are 2 for a point source (ra,dec), 5 for the deVauc or exp model, and 9 for the composite model.
The DECAM_RCHI2 values are interpreted as the reduced χ² pixelweighted by the model fit, computed as the following sum over pixels in the blob for each object:
The above sum is over all images contributing to a particular filter. The above can be negativevalued for sources that have a flux measured as negative in some bands where they are not detected.
SDSS_TREATED_AS_POINTSOURCE indicated whether an object was initialized as an SDSS point source (if "T") or galaxy (if "F"). This is based upon the SDSS morphological classifications, where SDSS_OBJTYPE=6 indicates a point source and =3 indicates a galaxy. However, SDSS_TREATED_AS_POINTSOURCE is also set to "T" for sources satisfying any of the following conditions: the effective radius is measured as S/N less than 3, sources with very large flux, the effective radius reported is the largest allowed, or the effective radius S/N is larger than expected given the measured flux of the objects. These are almost the same conditions as described in Lang et al 2014 (http://arxiv.org/abs/1410.7397), and are further described there.
Galactic Extinction Coefficients
The Galactic extinction values are derived from the SFD98 maps, but with updated coefficients to convert E(BV) to the extinction in each filter. These are reported in linear units of transmission, with 1 representing a fully transparent region of the Milky Way and 0 representing a fully opaque region. The value can slightly exceed unity owing to noise in the SFD98 maps, although it is never below 0.
Extinction coefficients for the SDSS filters have been changed to the values recommended by Schlafly & Finkbeiner 2011 (http://arxiv.org/abs/1012.4804 ; Table 4) using the Fizpatrick 1999 extinction curve at R_V = 3.1 and their improved overall calibration of the SFD98 maps. These coefficients are A / E(BV) = 4.239, 3.303, 2.285, 1.698, 1.263 in ugriz, which are different from those used in SDSSI,II,III, but are the values used for SDSSIV/eBOSS target selection.
Extinction coefficients for the DECam filters also use the Schlafly & Finkbeiner 2011 values, with uband computed using the same formulae and code at airmass 1.3 (Schlafly, priv. comm. decamdata list on 11/13/14). These coefficients are \(A / E(BV)\) = 3.995, 3.214, 2.165, 1.592, 1.211, 1.064 for the DECam \(u\), \(g\), \(r\), \(i\), \(z\), \(Y\) filters, respectively. These are slightly different than the ones in Schlafly & Finkbeiner (http://arxiv.org/abs/1012.4804).
The coefficients for the four WISE filters are derived from Fitzpatrick 1999, as recommended by Schafly & Finkbeiner, considered better than either the Cardelli et al 1989 curves or the newer Fitzpatrick & Massa 2009 NIR curve not vetted beyond 2 micron). These coefficients are A / E(BV) = 0.184, 0.113, 0.0241, 0.00910.
Ellipticities
The ellipticity, ε, is different from the usual eccentricity, \(e \equiv \sqrt{1  (b/a)^2}\). In gravitational lensing studies, the ellipticity is taken to be a complex number:
Where ϕ is the position angle with a range of 180°, due to the ellipse's symmetry. Going between \(r, \epsilon_1, \epsilon_2\) and \(r, b/a, \phi\):