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) aboard the Spitzer Space Telescope provides low-spectral resolution (R ≈ 15–25) spectroscopy in the far-infrared using the MIPS 70 μm detector. A reflective grating provides a dispersion of 1.7 μm per pixel, and an effective wavelength coverage of 52.8–98.7 μm 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 μm 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.