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,N-1] and is contiguously enumerated within each blob | |

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 epoch J2000 |

RA_IVAR | float32 | 1/deg² | Inverse variance of RA, excluding astrometric calibration errors |

DEC | float64 | deg | Declination at epoch J2000 |

DEC_IVAR | float32 | 1/deg² | Inverse variance of DEC (no cos term!), excluding astrometric calibration errors |

BX | float32 | pix | X position (0-indexed) of coordinates in brick image stack |

BY | float32 | pix | Y position (0-indexed) of coordinates in brick image stack |

BX0 | float32 | pix | Initialized X position (0-indexed) of coordinates in brick image stack |

BY0 | float32 | pix | Initialized Y position (0-indexed) 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] | nanomaggies | DECam model flux in ugrizY |

DECAM_FLUX_IVAR | float32[6] | 1/nanomaggies² | Inverse variance oF DECAM_FLUX |

DECAM_APFLUX | float32[8,6] | nanomaggies | DECam aperture fluxes on the co-added 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] | nanomaggies | DECam aperture fluxes on the co-added residual images |

DECAM_APFLUX_IVAR | float32[8,6] | 1/nanomaggies² | 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 profile-weighted) | |

DECAM_RCHI2 | float32[6] | Profile-weighted χ² of model fit normalized by the number of pixels | |

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

DECAM_FRACMASKED | float32[6] | Profile-weighted 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] | nanomaggies | WISE model flux in W1,W2,W3,W4 |

WISE_FLUX_IVAR | float32[4] | 1/nanomaggies² | 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 profile-weighted) | |

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

WISE_RCHI2 | float32[4] | Profile-weighted χ² of model fit normalized by the number of pixels | |

DCHISQ | float32[4] | Difference in χ² between successfully more-complex model fits | |

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

FRACDEV_IVAR | float32 | Inverse variance of FRACDEV | |

SHAPEEXP_R | float32 | arcsec | Half-light 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 | Half-light 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(B-V) 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 http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

1 | 2 | saturated | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

2 | 4 | interpolated | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

4 | 16 | single exposure cosmic ray | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

6 | 64 | bleed trail | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

7 | 128 | multi-exposure transient | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

8 | 256 | edge | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

9 | 512 | edge2 | detailed at http://www.noao.edu/noao/staff/fvaldes/CPDocPrelim/PL201_3.html |

## Goodness-of-Fits

The DCHISQ values represent the penalized χ² of all the pixels compared to various models. This 4-element vectorcontains the χ² difference between the best-fit 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 pixel-weighted 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 negative-valued 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(B-V) 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(B-V) = 4.239, 3.303, 2.285, 1.698, 1.263 in ugriz, which are different from those used in SDSS-I,II,III, but are the values used for SDSS-IV/eBOSS target selection.

Extinction coefficients for the DECam filters also use the Schlafly & Finkbeiner 2011 values, with u-band computed using the same formulae and code at airmass 1.3 (Schlafly, priv. comm. decam-data list on 11/13/14). These coefficients are A / E(B-V) = 3.995, 3.214, 2.165, 1.592, 1.211, 1.064. (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(B-V) = 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 \(r, b/a, \phi\):

## Debugging Tags to Remove in the Future

The following are from the SDSS DR13 catalogs, to be released in 2015 as the SDSS-IV/eBOSS target selection catalogs.

Name | Type | Units | Description |
---|---|---|---|

SDSS_RUN | int32 | http://data.sdss3.org/datamodel/files/BOSS_PHOTOOBJ/RERUN/RUN/CAMCOL/photoObj.html | |

SDSS_CAMCOL | byte | ||

SDSS_FIELD | int32 | ||

SDSS_ID | int32 | ||

SDSS_OBJID | int64 | ||

SDSS_PARENT | int32 | ||

SDSS_NCHILD | int32 | ||

SDSS_OBJC_TYPE | int64 | ||

SDSS_OBJC_FLAGS | int64 | ||

SDSS_OBJC_FLAGS2 | int64 | ||

SDSS_FLAGS | int64[5] | ||

SDSS_FLAGS2 | int64[5] | ||

SDSS_TAI | float64[5] | ||

SDSS_RA | float64 | ||

SDSS_DEC | float64 | ||

SDSS_PSF_FWHM | float32[5] | ||

SDSS_MJD | int64 | ||

SDSS_THETA_DEV | float32[5] | ||

SDSS_THETA_DEVERR | float32[5] | ||

SDSS_AB_DEV | float32[5] | ||

SDSS_AB_DEVERR | float32[5] | ||

SDSS_THETA_EXP | float32[5] | ||

SDSS_THETA_EXPERR | float32[5] | ||

SDSS_AB_EXP | float32[5] | ||

SDSS_AB_EXPERR | float32[5] | ||

SDSS_FRACDEV | float32[5] | ||

SDSS_PHI_DEV_DEG | float32[5] | ||

SDSS_PHI_EXP_DEG | float32[5] | ||

SDSS_PSFFLUX | float32[5] | ||

SDSS_PSFFLUX_IVAR | float32[5] | ||

SDSS_CMODELFLUX | float32[5] | ||

SDSS_CMODELFLUX_IVAR | float32[5] | ||

SDSS_MODELFLUX | float32[5] | ||

SDSS_MODELFLUX_IVAR | float32[5] | ||

SDSS_DEVFLUX | float32[5] | ||

SDSS_DEVFLUX_IVAR | float32[5] | ||

SDSS_EXPFLUX | float32[5] | ||

SDSS_EXPFLUX_IVAR | float32[5] | ||

SDSS_EXTINCTION | float32[5] | ||

SDSS_CALIB_STATUS | int64[5] | ||

SDSS_RESOLVE_STATUS | int64 |

## Tags to Add in the Future

Name | Type | Units | Description |
---|---|---|---|

TAI_MIN | float64 | sec | TAI timestamp for the earliest DECam image contributing to this brick (any filter) |

TAI_MAX | float64 | sec | TAI timestamp for the latest DECam image contributing to this brick (any filter) |

EPOCH | float64 | year | Epoch for RA,DEC coordinates, equal to the Julian Date of observation if only 1 epoch |

PM_RA | float32 | mas/year | Proper motion in RA (actual milli-arcsec per year, not cos(dec) units as done in Hipparcos catalog |

PM_RA_IVAR | float32 | 1/(mas/year)² | Inverse variance of PM_RA |

PM_DEC | float32 | mas/year | Proper motion in DEC |

PM_DEC_ISIG | float32 | 1/(mas/year)² | Inverse variance of PM_DEC |

PARALLAX | float32 | mas | Trigonometric parallax in milliarcsec; distance in parsecs equals 1000/PARALLAX |

PARALLAX_IVAR | float32 | 1/mas² | Inverse variance of PARALLAX |