SCATTERED-LIGHT IN THE ECHELLE MODES OF THE GODDARD HIGH-RESOLUTION SPECTROGRAPH ABOARD THE HUBBLE-SPACE-TELESCOPE .2. ANALYSIS OF IN-FLIGHT SPECTROSCOPIC OBSERVATIONS

We report on an analysis of observations made with the Goddard High Re solution Spectrograph (GHRS) aboard the Hubble Space Telescope for the purpose of calibrating the effects of scattered light. The data were obtained during the first 2 years of flight operations as part of the Science Verification, Science Assessment Observations, and Guaranteed Time Observations programs. Data from the two high-resolution echelle modes, three of the four medium-resolution gratings, and both science apertures have been studied. Both the general level of background ligh t near the spectra and the filling in of the cores of saturated inters tellar absorption lines have been determined as functions of grating, order, wavelength, and aperture. The behavior is in accordance with ou r detailed analysis of prelaunch laboratory data and validates both th e observing procedures and the data reduction developed on the basis o f that experience. We present and discuss the use of a background (sca ttered light) removal algorithm designed to produce net spectra proper ly corrected for the effects of grating scattered light. The coefficie nts of the scattered light removal algorithm have been determined, and recommended numerical values are presented. Results of using the algo rithm are presented for a diverse group of stellar, circumstellar, and interstellar spectra which demonstrate the utility of these technique s and illustrate the quality of data attainable with the GHRS and the HST.