XUV Photometer System

XUV Photometer System
Name	XUV Photometer System
Instrument type	Photometer
Wavelength range	Extreme ultraviolet
Operator	NASA
Manufacturer	University of California, Berkeley
Launched	1992
Mission duration	~9 months

XUV Photometer System. The XUV Photometer System was a pioneering scientific instrument designed to observe the cosmos in the extreme ultraviolet portion of the electromagnetic spectrum. It was the primary payload aboard the NASA satellite Extreme Ultraviolet Explorer (EUVE), which launched in 1992. The system's successful operation marked a significant expansion of observational astronomy, revealing previously unseen celestial sources and mapping the interstellar medium.

Overview

The development of the XUV Photometer System was driven by the need to explore a largely uncharted region of the electromagnetic spectrum. Prior to its launch, the extreme ultraviolet band was heavily obscured for distant observations due to absorption by neutral hydrogen in the Milky Way. The instrument was conceived and built by a team at the University of California, Berkeley Space Sciences Laboratory, led by principal investigator Stuart Bowyer. Its deployment on the Extreme Ultraviolet Explorer mission, part of NASA's Explorers Program, provided the first all-sky survey in this critical wavelength range, complementing earlier surveys like those from the Einstein Observatory and International Ultraviolet Explorer.

Design and Components

The system comprised three distinct scanning photometers and a deep survey spectrometer, each tailored for specific observational tasks. The scanning instruments utilized aluminum and carbon filters in combination with boron doped silicon photodiodes to isolate different EUV bands. This filter-wheel design allowed for broadband photometry and crude spectral differentiation. The deep survey component employed a Wolter telescope design, similar to those used on the ROSAT and Chandra X-ray Observatory, to focus EUV radiation onto a microchannel plate detector. The entire system was housed within the EUVE satellite bus, with thermal control managed by the Goddard Space Flight Center and attitude data provided by star trackers from the Jet Propulsion Laboratory.

Scientific Objectives and Applications

The primary objective was to conduct the first comprehensive all-sky survey in the extreme ultraviolet, aiming to catalog sources such as white dwarf stars, cataclysmic variable stars, and active coronae of late-type stars. A key application was studying the local interstellar medium, particularly measuring the density and ionization state of nearby interstellar clouds like the Local Bubble. The data also contributed to understanding the stellar evolution of hot, compact objects and provided crucial observations for the field of high-energy astrophysics. Findings were cross-referenced with data from other missions, including the Hubble Space Telescope and the Voyager program.

Operational History

The XUV Photometer System was launched aboard the Extreme Ultraviolet Explorer satellite on June 7, 1992, from Cape Canaveral Air Force Station using a Delta II rocket. The all-sky survey phase lasted approximately six months, after which the mission entered a pointed observation phase targeting specific objects of interest. The instrument operated successfully until January 2001, when the EUVE satellite was deliberately decommissioned and deorbited, far exceeding its planned mission duration. Operations were conducted from the University of California, Berkeley and involved collaboration with scientists from the Massachusetts Institute of Technology and the Smithsonian Astrophysical Observatory.

Technical Specifications

The scanning photometers covered three primary bandpasses centered at approximately 100 Å (Lexan/Boron), 200 Å (Aluminum/Carbon), and 400 Å (Titanium/Antimony). The deep survey spectrometer had a spectral resolution (λ/Δλ) of about 200 across its 70–760 Å range. The field of view for the scanners was roughly 2° x 90°, while the deep survey telescope had a 2° field. Detector quantum efficiency ranged from 10% to 30% across the bands. The instrument's data was processed by an onboard computer and transmitted via the Tracking and Data Relay Satellite System to ground stations.

Data and Results

The system produced the first EUV all-sky maps, cataloging over 800 sources, including many previously undetected white dwarfs like GD 246 and cataclysmic variables such as SS Cygni. It provided critical measurements of the interstellar medium, constraining the opacity of the galactic plane and the properties of the Local Bubble. The deep survey yielded low-resolution spectra for hundreds of objects, contributing to studies of stellar atmospheres and accretion disk physics. The resulting EUVE Source Catalog became a foundational resource for subsequent missions like the XMM-Newton and Swift Gamma-Ray Burst Mission.

Category:Space telescopes Category:NASA spacecraft instruments Category:Extreme ultraviolet astronomy