Summary of the WISE -> DVO interpretations

(Up to DVO Top Level)

This page describes the translation between data fields in the WISE Preliminary Release (Apr 2011) and the DVO data fields, primarily in the 'measure' table.

Some useful links:

In the WISE Preliminary Data Release, all sources are described by the equivalent of a single database row, with separate fields in the row for W1-W4 specific measurements, and some fields common to all three filters. For example, the coordinates and observing time are all given as a single value for all three filters. In the conversion to the DVO representation, each measurement of an object is converted to a separate DVO measurement entry. All WISE sources are guaranteed to have all four measurements instantiated, but in some cases the measurements may be upper limits (non-detections in those filters). Below, we list the relationship between the WISE information on the left side of the -> and the DVO measurement field on the right side. Values which are defined for the 4 bands separately use the short cut 'w?value' to mean W1 value, W2 value, etc. Each measurement has one of the 4 WISE photcodes, as appropriate (

  • ra, dec : recorded using the DVO standard of delta RA,DEC relative to the object's average RA,DEC location.
  • sigra, sigdec -> dXccd, dYccd : 'note that these are defined for perfect 1 arcsec pixels, not the real WISE pixels. -- the values of pltscale and posangle are defined to be 1.0 and 0.0 respectively'
  • w?mpro -> M
  • w?sigmpro -> dM
  • w?rchi2m -> psfChisq
  • wx, wy -> Xccd, Yccd : see the note above about dXccd, dYccd. These are not on the same system.
  • the measure.t (time) value is set to the midpoint of the WISE preliminary data release time period, since no epoch information is supplied (and the measurements are derived from a stack of multiple exposures in any case). This date is 2010/03/07,12:00:00 (JD = 2455263.0).

The following WISE values are used to set bits in the phot_flags field:

  • ph_qual:

A = 0x0000.0001 Source is detected in this band with a flux signal-to-noise ratio w?snr>10.

B = 0x0000.0002 Source is detected in this band with a flux signal-to-noise ratio 3<w?snr<10.

C = 0x0000.0004 Source is detected in this band with a flux signal-to-noise ratio 2<w?snr<3..

U = 0x0000.0008 Upper limit on magnitude. Source measurement has w?snr<2. The profile-fit magnitude w?mpro is a 95% confidence upper limit.

X = 0x0000.0010 profile-fit measurement was not possible at this location possible in this band. The value of w?mpro and w?sigmpro will be "null" in this band.

  • cc_flag:

p,P = 0x0001.0000 Persistence. Source may be a spurious detection of or contaminated by a latent image left by a bright star.

h,H = 0x0002.0000 Halo. Source photometry may be a spurious detection of or contaminated by the scattered light halo surrounding a nearby bright source

o,O = 0x0002.0000 Optical ghost. Source may be a spurious detection of or contaminated by an optical ghost image caused by a nearby bright source (note bit is overloaded)

d,D = 0x0004.0000 Diffraction spike. Source may be a spurious detection of or contaminated by a diffraction spike from a nearby bright star on the same image.

Note that the UPPER case entries are thought to be spurious sources and are also flagged with the value 0x0008.0000 in the phot_flags field. Lower case entries are thought to be real source, though affected by the contaminating feature.

  • saturation : w?sat > 0.0 -> 0x0000.0100 At least one saturated pixel in W?
  • deblending :
    • nb > 1 and na = 0 -> 0x0010.0000 : more than 1 PSF fitted, passively deblended
    • nb > 1 and na = 1 -> 0x0020.0000 : more than 1 PSF fitted, actively deblended
  • extendedness : if ext_flg == 1 -> 0x0100.0000 (source is thought to be extended)
  • variability : for var_flg of:
    • 1-4 -> 0x1000.0000 : probably not variable
    • 5-7 -> 0x2000.0000 : possibly variably
    • 8-9 -> 0x4000.0000 : likely variable