The Far Infrared Absolute Spectrophotometer (FIRAS): Cosmic Background Spectrum, Dipole and Distortions
Abstract
The FIRAS (Far Infrared Absolute Spectrophotometer) instrument on the COBE(dag ) is designed to measure differences between the cosmic microwave background spectrum and the theoretically predicted blackbody spectrum. This paper reports details of the calibration and analysis methods used to achieve accuracy and precision of better than 0.05% of the peak brightness from 2 to 20 cm(-1) . The calibration is done by least squares fitting of an instrument model to observations of the calibration blackbodies and horn antennas at a wide variety of temperatures. The model includes the bolometer detectors, the emissivities of the IR sources, and error parameters for vibrations, thermometer noise and calibration, and multipass radiation. The analysis of the sky includes fits to a uniform (CBR), dipole, and an average galactic spectrum. The fits, residuals, and error estimates leading to these spectra will be shown, and the spectra will be compared with predictions and the y and mu distortion. Limits for mu and y will be reported along with the best values and their errors for the CBR temperature, the dipole amplitude, the dipole color temperature, and an estimate for the galactic radiation at the galactic poles. () COBE is supported by NASA's Astrophysics Division. Goddard Space Flight Center (GSFC), under the scientific guidance of the COBE Science Working Group, is responsible for the development and operation of COBE.
- Publication:
-
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1992
- Bibcode:
- 1992AAS...181.1807F