AAS 202nd Meeting, May 2003
Session 4 Instrumentation: Space Missions
Poster, Monday, May 26, 2003, 9:20am-6:30pm, West Exhibit Hall

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[4.08] Operations of the Far Ultraviolet Spectroscopic Explorer : A `Dynamic' Flux Calibration.

D. Ehrenreich, J. Dupuis, W.V. Dixon, D.J. Sahnow, J.W. Kruk (JHU)

The FUSE flux calibration is based on model-atmosphere predictions of the spectra of well studied white-dwarf stars. Calibration operations, however, are a highly `dynamic' process consisting of repeatedly measuring these standard stars, deriving corrections, and integrating the results into CALFUSE, the FUSE science pipeline. With suitable scheduling, those calibration observation campaigns let us characterize short term and long term variations of the sensitivity. One particular issue addressed by these observations is monitoring possible degradation of the FUSE optical coatings by atomic oxygen present in the upper atmosphere. We have attempted to minimize this by avoiding pointing close to the instantaneous velocity vector of the spacecraft (the ram vector). Prior to Cycle 3, the minimum permitted angle between the line of sight and the ram vector was 20 degrees. This was reduced to 15 degrees during Cycle 3 to increase our sky coverage, and will be further reduced to 10 degrees for Cycle 4. This relaxation of ram constraints has been preceded by a tailored calibration program in which white dwarf measurements are obtained before and after observations performed for a limited time below the current ram vector constraint. This relaxation of the ram vector constraint will considerably expand the ability of FUSE to observe sources at low declination.

This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U.S. participants has been provided by NASA contract NAS5-32985.

If you would like more information about this abstract, please follow the link to http://fuse.pha.jhu.edu. 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: david@pha.jhu.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.