Data model: xdcore

General Description
The xdcore files contain quasar probabilities in three redshift ranges derived using the XDQSO technique, as described in Bovy et al. (2011). The quasar probabilities are assigned based on models for the underlying flux distributions of quasars and stars applied to the single-epoch ugriz fluxes of all 160,904,060 point-sources with dereddened i-band magnitude between 17.75 and 22.45 mag in DR8.
Naming Convention
xdcore_[0-9]{6}\.fits, where [0-9]{6} is the six-digit, zero-padded run number.
Approximate Size
File Type
Read by Products
Written by Products

HDU0: Empty

This HDU is intentionally left empty.

Required Header Keywords
SIMPLETboolConforms to FITS standard.
BITPIX8intDummy header
NAXIS0intDummy header
EXTENDTboolExtensions may be present

HDU1: Quasar probabilities

HDU 1 contains quasar probabilities based on single-epoch SDSS ugriz data as described in the binary table documented below.

Note: Additional HDUs (past HDU1) may be present for engineering purposes, but are not supported and are subject to change. Users should refrain from using HDUs not listed here.

Required Header Keywords
TFIELDS27intNumber of columns in table
Required Columns
OBJIDchar[22]Unique SDSS identifier composed from [skyVersion,rerun,run,camcol,field,obj].
RUNint32SDSS imaging run number
RERUNchar[3]SDSS processing rerun number
CAMCOLint32Camera column
FIELDint32Field number
IDint32The object ID within a field
RAfloat64Right ascension in decimal degrees (J2000.0)
DECfloat64Declination in decimal degrees (J2000.0)
QSOLOWZLIKEfloat64Relative-flux density factor p({f_j/f_i} | f_i,z < 2.2 quasar)
QSOMIDZLIKEfloat64Same as previous, but for 2.2 <= z <= 3.5 quasar
QSOHIZLIKEfloat64Same as previous, but for z > 3.5 quasar
STARLIKEfloat64Same as previous, but for star
QSOLOWZNUMBERfloat64Number density as a function of apparent magnitude for this object for the z < 2.2 quasar class
QSOMIDZNUMBERfloat64Same as previous, but for 2.2 <= z <= 3.5 quasar
QSOHIZNUMBERfloat64Same as previous, but for z > 3.5 quasar
STARNUMBERfloat64Same as previous, but for star
PSTARfloat64Probability that the object is a star
PQSOLOWZfloat64Probability that the object is a z < 2.2 quasar
PQSOMIDZfloat64Probability that the object is a 2.2 <= z <= 3.5 quasar
PQSOHIZfloat64Probability that the object is a z > 3.5 quasar
PQSOfloat64Probability that the object is a quasar (sum of previous three)
BITMASKint64BOSS quasar target selection bitmask (see Sheldon et al., 2011, in preparation; appendix A of Bovy et al. 2011)
GOODint16good flag: 0: passes all BOSS cuts, 1: fails basic BOSS cut (see paper), 2: fails other BOSS cuts (see Bovy et al. 2011).
PHOTOMETRICint16Indicates whether this object was observed under good imaging conditions (True/False)
PSFMAGfloat64[5]PSF Uebercalibrated ugriz asinh magnitude (corrected for Galactic extinction)
PSFMAGERRfloat64[5]Error in PSF ugriz asinh magnitude
EXTINCTION_Ufloat64Extinction in u band; Au/Ag/Ar/Ai/Az= 5.155/3.793/2.751/2.086/1.479