DES-SDSS Color Terms

SV requirements and goals associated with this analysis


  • Synthetic SDSS ugriz, UKIDSS Yab, and DES grizY magnitudes were
    generated by Sahar Allam using the Pickles (1998) stellar library
    and David James' and Huan Lin's DES filter response curves from
  • Real DECam data were taken from the NCSA DESDM standard star processing for
    the night of November 3 (griz). (For Y-band, the data were taken from
    Huan Lin's coadd of the November 2 and 4 starflat.)
  • Plots of "mag_DES - mag_SDSS" vs. SDSS color were generated for both sets
    of data and compared:

  • Results of fit of the above plots to a straight line
    (the color term coefficient "b" is then the slope of
    the straight line):
filter range of fit b_synth b_observed b_synth - b_observed Comments for Cal-R2/Cal-R3
g 0 < g-r < 1 -0.084 -0.103 +0.019 w/in spec
r 0 < g-r < 1 -0.087 -0.080 -0.007 w/in spec
i 0 < i-z < 1 -0.324 -0.298 -0.026 marginally out of spec
z 0 < i-z < 1 -0.080 -0.086 +0.006 w/in spec
Y -0.3 < z-Y < 0.3 +0.409 +0.261 +0.148 out of spec

Results (as of Nov 24, 2012)

  • The Cal-R2 requirement has been met.
  • g w/in spec
  • r w/in spec
  • i marginally out-of-spec
  • z w/in spec
  • The Cal-R3 requirement has not been met.
  • Y out of spec
  • The observed color term is shallower than expected.
  • It does, however, have the right sign and generally the right shape.
  • That said, I would not delay DES operations on account of failing to meet this particular requirement.
  • The Cal-G7 goal has not yet been met.
  • g not in spec
  • r not in spec
  • i not in spec
  • z not in spec
  • Y not in spec

Attached Files