Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer: IV. The Spectral Energy Distribution Mode

The Spectral Energy Distribution (SED) mode of the Multiband Imaging Photometer for Spitzer (MIPS) Space Telescope provides low-spectral resolution (R ~ 15-25) spectroscopy in the far infrared using the MIPS 70 um detector. A reflective grating provides a dispersion of 1.7 um per pixel, and an effective wavelength coverage of 52.8--98.7 um over detector rows 1-27. The final 5 detector rows are contaminated by second-order diffracted light and are left uncalibrated. The flux calibration is based on observations of MIPS calibration stars with 70 um flux densities of 0.5--15 Jy. The point-source flux calibration accuracy is estimated to be 10% or better down to about 0.5 Jy at the blue end of the spectrum and to 2 Jy near the red end. With additional uncertainties from the illumination and aperture corrections included, the surface brightness calibration of extended sources is accurate to ~15%. Repeatability of better than 5% is found for the SED mode through multiple measurements of several calibration stars.