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About BEFS

ORFEUS-SPAS II

   Berkeley Extreme and Far-UV Spectrometer (BEFS) flew    the Orbiting and Retrievable Far and Extreme Ultraviolet   Spectrograph (ORFEUS)-SPAS for 5 days in September   1993 and again for 14 days in November 1996.


The picture shows the ORFEUS-SPAS during checkout on the shuttle arm prior to deployment during the first flight. The BEFS is clearly visible at the prime focus of the telescope. The two electronics boxes to the right of the telescope (in partial shadow) contain the supporting electronics. Extending from the telescope tube to the left is the AIT/LSW Echelle spectrometer. The small telescope in the foreground is the Astro-SPAS star tracker; the long, shiny tube on the far side of the platform is Princeton's IMAPS experiment.

The ORFEUS telescope is 1 meter in diameter and 4 meters long . The Berkeley spectrometer sits at the prime focus of the f/2.4 normal incidence primary mirror. This instrument is designed to provide high-resolution (/5000) spectroscopy of point sources between 390 and 1200 Å simultaneously, with an effective area of about 4 - 6 cm2. Alternatively, an off-axis paraboloidal mirror can be driven into the light path, collimating the beam and directing it into an Echelle spectrometer provided by AIT and the Landessternwarte Heidelberg (LSW). That instrument is designed to provide /10,000 spectroscopy of point sources between 900 and 1250 at somewhat lower sensitivity.

The resolution of the ORFEUS spectrometers significantly exceeds that of other instruments with comparable sensitivity at wavelengths of overlap. Below 760 , the spectrometers on the Extreme Ultraviolet Explorer offer somewhat lower sensitivity (but longer observing times), and a resolution of /300. Between 800 and 1250 , the Hopkins Ultraviolet Telescope offers higher sensitivity, and comparable observing times, but again the resolution is about /300. The Hubble Space Telescope is limited to wavelengths longer than about 1170 Å. FUSE, the Far Ultraviolet Spectroscopic Explorer, can achieve a resolution as great as /30,000 in this wave band, but cannot observe objects brighter than 1.0x10-10 ergs cm-2 s-1 Å-1. The ORFEUS and FUSE data sets are thus complimentary.

Information about the instrument was taken from Hurwitz, M., & Bowyer, S., "The Berkeley Spectrometer for ORFEUS: Laboratory and In-Flight Performance" in Astrophysics in the Extreme Ultraviolet, ed. S Bowyer & R. F. Malina (Dordrecht: Kluwer Academic Publishers), 601-609, 1996