msigcom

The First and Second Incremental Release PSCs included a "combined" uncertainty column, ?_msigcom, that was designed to give a measure of the total photometric uncertainty including global and systemmatic terms. The value of ?_msigcom for each band used in the IDR's was:

where

msig = Extraction uncertainty (i.e. default magnitude msig)
zperr = Nightly photometric zero point uncertainty
fferr = Flat-fielding residual error (taken to be 0.005 mags)
r1normrms = R1 normalization uncertainty (applied to R1 sources only)

For the All-Sky PSC, there are several questions that must be addressed if this form of msigcom is to be used:

1. Is this form still appropriate?
2. Should the corrected values of msig be used for R2 sources?
3. There is no nightly J-band zperr available since a piecewise fit was usually used to derive the zero-point correction. What should be used in its place? See John Carpenter's summary.
4. The R1 normalization was taken from a look-up table for final processing. What value for r1normrms should be used?

All-Sky PSC

Discussion during the 8/13/02 Science Team telecon concluded with this agreement for the form of msigcom in the All-Sky PSC release:

where

• [jhk]_cmsig = Corrected extraction uncertainty.



• [jhk]_zperr = Constant, band-dependent photometric zero point uncertainty. Derived from analysis of internal accuracy of photometric calibration in final processing



• j_zperr = 0.011
• h_zperr = 0.007
• k_zperr = 0.007



• fferr = 0.005 mags (as before)



• r1normrms = 0.012 mags
  

  Constant R1 normalization uncertainty (applied to R1 sources only). Derived to be the mean normalization uncertainties for all PSF's in the look-up table for final processing.

Last Updated: 13 August 2002
R. Cutri (IPAC)