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Published June 2008 | Published
Journal Article Open

Absolute physical calibration in the infrared


We determine an absolute calibration for the Multiband Imaging Photometer for Spitzer 24 μm band and recommend adjustments to the published calibrations for Two Micron All Sky Survey (2MASS), Infrared Array Camera (IRAC), and IRAS photometry to put them on the same scale. We show that consistent results are obtained by basing the calibration on either an average A0V star spectral energy distribution (SED), or by using the absolutely calibrated SED of the Sun in comparison with solar-type stellar photometry (the solar analog method). After the rejection of a small number of stars with anomalous SEDs (or bad measurements), upper limits of ~1.5% root mean square (rms) are placed on the intrinsic infrared (IR) SED variations in both A-dwarf and solar-type stars. These types of stars are therefore suitable as general-purpose standard stars in the IR. We provide absolutely calibrated SEDs for a standard zero magnitude A star and for the Sun to allow extending this work to any other IR photometric system. They allow the recommended calibration to be applied from 1 to 25 μm with an accuracy of ~2%, and with even higher accuracy at specific wavelengths such as 2.2, 10.6, and 24 μm, near which there are direct measurements. However, we confirm earlier indications that Vega does not behave as a typical A0V star between the visible and the IR, making it problematic as the defining star for photometric systems. The integration of measurements of the Sun with those of solar-type stars also provides an accurate estimate of the solar SED from 1 through 30 μm, which we show agrees with theoretical models.

Additional Information

© 2008 The American Astronomical Society. Received 2008 January 16; accepted 2008 March 14; published 2008 May 13. We thank Tom Ayres, Martin Cohen, Chris Corbally, Mark Kidger, Gerry Neugebauer, Stephen Price, Murray Silverstone, and Gerard Thuillier for helpful discussions. This publication makes use of data products from the TwoMicronAll Sky Survey, which is a joint project of the University of Massachusetts and the IR Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research also has made use of the SIMBAD database, operated at CDS, Strasbourg, France. It also made use of the NASA/IPAC IR Science Archive. This work was supported through contracts 1255094 issued by JPL through CalTech and NAG5-12318 from NASA/Goddard to the University of Arizona.

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