AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 16. Solar Corona
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southeast Exhibit Hall

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[16.06] The SERTS-97 Cross-Calibration of CDS & EIT on SOHO

R.J. Thomas, J.M. Davila, W.T. Thompson (NASA/GSFC), B.J. Kent (RAL), J. Hollandt (PTB)

GSFC's Solar EUV Rocket Telescope and Spectrograph (SERTS) obtains imaged high-resolution spectra of individual solar features, giving information about the Sun's corona and upper transition region. Its flight on 1997 November 18 had the additional goal of providing radiometric and wavelength calibrations for several experiments on the Solar and Heliospheric Observatory (SOHO) satellite mission. For that purpose, an end-to-end radiometric calibration of the rocket instrument was carried out at RAL in the same facility used to characterize the CDS experiment on SOHO, and using the same EUV light source specially re-calibrated by PTB against the synchrotron radiation of the electron storage ring BESSY, which is a primary EUV radiometric standard. Scans of the SERTS aperture over a range of pitch and yaw angles were made to determine the instrument's absolute spectral sensitivity to \le 25% at 12 wavelengths covering its range of 300 -- 365~Å. Also, pre- and post-flight wavelength calibrations were done at GSFC using well known lines of He~II and Ne~II within the SERTS bandpass. For the first time, SERTS-97 carried an EUV solar flux monitor kindly provided by USC; its readings were used to validate our calculations of atmospheric EUV transmission over the rocket's trajectory. During the flight, SERTS-97 and CDS observed the same solar locations, as demonstrated by subsequent data co-registration with EIT images, allowing the SERTS calibrations to be directly applied to both CDS and EIT. Since SERTS clearly resolves the strong Si~XI and He~II lines blended in EIT's 304~Å\ channel, SERTS measurements give information on the spectral composition of these images as well. Examples of the various cross-calibrations will be shown.

This work has been supported through RTOP grants for the SERTS and SOHO programs from the Solar Physics Office of NASA's Space Physics Division.

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