SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: PLANETS AND CELESTIAL CALIBRATION SOURCES
- ADNET Systems, Inc., 7515 Mission Dr., Suite A100 Lanham, MD 20706 (United States)
- Code 665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Department of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544-0708 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218-2686 (United States)
- Astrophysics, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom)
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)
- Department of Astronomy, University of Texas, 2511 Speedway, RLM 15.306, Austin, TX 78712 (United States)
- Columbia Astrophysics Laboratory, 550 W. 120th St., Mail Code 5247, New York, NY 10027-6902 (United States)
- Departments of Astrophysics and Physics, KICP and EFI, University of Chicago, Chicago, IL 60637 (United States)
- Canadian Institute for Theoretical Astrophysics, 60 St. George St, University of Toronto, Toronto, ON M5S 3H8 (Canada)
We present WMAP seven-year observations of bright sources which are often used as calibrators at microwave frequencies. Ten objects are studied in five frequency bands (23-94 GHz): the outer planets (Mars, Jupiter, Saturn, Uranus, and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg A, 3C274, and 3C58). The seven-year analysis of Jupiter provides temperatures which are within 1{sigma} of the previously published WMAP five-year values, with slightly tighter constraints on variability with orbital phase (0.2% {+-} 0.4%), and limits (but no detections) on linear polarization. Observed temperatures for both Mars and Saturn vary significantly with viewing geometry. Scaling factors are provided which, when multiplied by the Wright Mars thermal model predictions at 350 {mu}m, reproduce WMAP seasonally averaged observations of Mars within {approx}2%. An empirical model is described which fits brightness variations of Saturn due to geometrical effects and can be used to predict the WMAP observations to within 3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated. Uncertainties in Uranus temperatures are 3%-4% in the 41, 61, and 94 GHz bands; the smallest uncertainty for Neptune is 8% for the 94 GHz band. Intriguingly, the spectrum of Uranus appears to show a dip at {approx}30 GHz of unidentified origin, although the feature is not of high statistical significance. Flux densities for the five selected fixed celestial sources are derived from the seven-year WMAP sky maps and are tabulated for Stokes I, Q, and U, along with polarization fraction and position angle. Fractional uncertainties for the Stokes I fluxes are typically 1% to 3%. Source variability over the seven-year baseline is also estimated. Significant secular decrease is seen for Cas A and Tau A: our results are consistent with a frequency-independent decrease of about 0.53% per year for Cas A and 0.22% per year for Tau A. We present WMAP polarization data with uncertainties of a few percent for Tau A. Where appropriate, WMAP results are compared against previous findings in the literature. With an absolute calibration uncertainty of 0.2%, WMAP data are a valuable asset for calibration work.
- OSTI ID:
- 21560535
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 192, Issue 2; Other Information: DOI: 10.1088/0067-0049/192/2/19; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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