Far-Ultraviolet Performance of the Berkeley Spectrograph during the ORFEUS-SPAS II Mission

The Berkeley spectrograph aboard the ORFEUS telescope made its second flight on the 14 day ORFEUS-SPAS II mission of the Space Shuttle Columbia in 1996 November/December. Approximately half of the available observing time was dedicated to the Berkeley spectrograph, which was used by both principal and guest investigators. The spectrograph's full bandpass is 390-1218 Å here we discuss its in-flight performance at far-ultraviolet wavelengths, at which most of the observations were performed. The instrument's effective area peaks at 8.9+/-0.5 cm² near 1020 Å, and the mean spectral resolution is 95 km s^-1 FWHM for point sources. Over most of the spectral range, the typical nighttime background event rate in each spectral resolution element was ~0.003 s^-1. Simultaneous background observations of an adjacent blank field were provided through a secondary, off-axis aperture. The Berkeley spectrograph's unique combination of sensitivity and resolution provided valuable observations of approximately 105 distinct astronomical targets, which ranged in distance from the Earth's own Moon to some of the brightest active galactic nuclei.

Based on the development and utilization of ORFEUS (Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometers), a collaboration of the Institute for Astronomy and Astrophysics of the University of Tübingen, the Space Astrophysics Group, University of California, Berkeley, and the Landessternwarte Heidelberg.