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E. F. Milone (RAO, U. Calgary), A. T. Young (SDSU)
The well-known past limitations in accuracy and precision of infrared photometry has been shown to be due primarily to atmospheric features within passbands and the use of the edges of the atmospheric windows to define those passbands. The saturation of portions of the passbands high in the atmosphere means, especially for the longer wavelength passbands, a large difference between a linearly extrapolated zero-air mass magnitude and the actual value. The rapid curvature of the extinction curve between 1 and 0 air mass is known as the Forbes effect. Since the strengths of atmospheric features vary with altitude and the circumstances of each site, different observatories have responded to the problem by redefining the Johnson system from J to Q to suit the needs of the site. The result has been a proliferation of systems, with filters having been selected for maximum throughput and so not necessarily placed, shaped, and narrowed to minimize optimally the effects of the absorption bands of the terrestrial atmosphere. Given this situation and in light of the tremendous promise of high precision presented by infrared photometry, and with the support of an important segment of the IR community, the Infrared Astronomy Working Group (IRWG) was created inside IAU Com. 25 to solve the problem. A subgroup of the IRWG consisting of Young, Milone, and Stagg set about examining the properties of existing passbands and in optimizing the placement and width of passbands within the atmospheric windows.
Here we review the transformation properties of the recommended Z to Q passbands and of the IR filters produced by Custom Scientific Co. to approximate the near IR passbands of this set, their signal to noise ratios, and results of the standardization testing project at the Rothney Astrophysical Observatory over the past few years. The extinction coefficients determined with the manufactured filters demonstrate the usefulness of these passbands for transformation to the standard system from a variety of observatory sites from 1 km to 4.3 km altitude and under a variety of atmospheric models. We compare the IRWG passbands' performance with that of older systems and of the recently discussed MKO-NIR system, which, we are pleased to note, was based to some extent on the work by the IRWG.
This work has been supported by grants to EFM from the Natural Sciences and Research Council of Canada of Canada and from the University Research Grants Committee of the University of Calgary.
If you would like more information about this abstract, please follow the link to http://www.ucalgary.ca/~milone/IRWG/. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.
The author(s) of this abstract have provided an email address for comments about the abstract: milone@ucalgary.ca
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.