Spectral Irradiance Calibration in the Infrared. XIII. "Supertemplates" and On-Orbit Calibrators for SIRTF's Infrared Array Camera (IRAC)

Abstract
We describe the technique used to develop on-orbit calibrators for IRAC and validate the method for either K0-M0III or A0-A5V stars. For SIRTF, the approach uses all available optical, NIR, and MIR photometry, and yields absolute spectra from UV to MIR. One set of stars is from Landolt's network of optical standards, the other from Carter-Meadows IR standards. Traceability to the Cohen-Walker- Witteborn framework of absolute photometry and spectra is assured. The method is based on using either "supertemplates" to represent the intrinsic shapes of the spectra of K0-M0IIIs from 1150A to 35 um, or Kurucz synthetic spectra for A0-5V stars. Each supertemplate/model is reddened according to a star's extinction and normalized by characterized optical photometry. This paper tests our ability to predict NIR (JHK) magnitudes from supertemplates or models constrained by Hippa- rcos/Tycho or precision ground-based optical data. We offer absolute calibrated spectra of 33 optical standards to demonstrate the viability of this technique for a set of IR calibrators 100-1000 times fainter than we have previously publ- ished. We calculate the absolute uncertainties associated with predicting IRAC mags for the faintest cool giant and hot dwarf in this new set of calibrators.

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