Update to Standards - 11/16/98

A new set of secondary standards were derived by Sergei Nikolaev of UMASS for 28 of the 41 calibration fields.
Information regarding how these were derived can be found here and an ascii list can be found here.
Of the thirteen remaining calibration fields, eleven are still in need of secondary standards.

The following documents the process taken at IPAC to adjust the selection of the secondary standards and improve magnitudes and postions where necessary:

• Magnitudes from UMASS standards (primary and secondary) were scaled by the mean magnitude difference in the primary standards in J / H and K bands.
• A visual inspection was made of all the secondary standards using representative coadds. Those that appeared to be within a confused area were rejected.
• To minimize the impact of the variable cross scan PSF, all secondaries from the original set (not the UMASS set) were edited based on proximity to the center of the calibration field. All that fell outside +/- 2 arcminutes of the center in cross-scan were rejected. An exception was in M67 where one of the primary standards, FS15, fell outside this window but was kept due to it being a primary standard.
• Positions of primary standards were checked and improved, if necessary, using smerge tool.
• Some secondary standards received previously from UMASS or generated at IPAC were not included in the latest secondary set. The magnitudes of these pre-existing standards were normalized by the mean magnitude difference in the pre-existing secondary standards that were included in the latest set. The mean magnitude difference was computed for each calibration field, independently. For those calibration fields where none of the secondary standards were included in the current set, the magnitudes for the pre-existing secondary standards remained unaltered.