Hopkins Ultraviolet Telescope
Hopkins Ultraviolet Telescope
Space MissionsIntroduction
The Hopkins Ultraviolet Telescope (HUT) was one of three ultraviolet instruments of the ASTRO-1 mission flown on the space shuttle Columbia during 2-10 December 1990.
HUT obtained 106 spectrophotometric observations of 77 targets in the far-UV (i.e., 912-1850 Å) at a resolution of ~3 Å. A few sources were observed in the 415-912 Å region with a 1.5 Å resolution. The same three instruments were later flown on the space shuttle Endeavour from 3-17 March 1995 as part of the ASTRO-2 mission. During the longer ASTRO-2 mission, 385 observations of 265 targets were obtained.
Hopkins Ultraviolet Telescope - ASTRO-1 on STS-35.
Hopkins Ultraviolet Telescope - ASTRO-1 on STS-35. (Source: NASA.)
HUT was conceived, designed, and built by astronomers and engineers at Johns Hopkins University to perform astronomical observations in the far-ultraviolet portion of the electromagnetic spectrum, wavelengths of light that are inaccessible to ground-based telescopes. HUT's primary purpose is to observe wavelengths of light that are too short to be seen with the Hubble Space Telescope, although overlap is provided to allow direct comparison.
The telescope has flown twice aboard the space shuttle, once in December 1990 (ASTRO-1) and again in March 1995 (ASTRO-2), as part of a package of instruments called the Astro Observatory. HUT has been used to observe hundreds of objects, ranging from nearby stars and planets to the most distant objects known in the Universe, the quasars.
HUT Technical Summary
| Principal Investigator: | Dr. Arthur F. Davidsen |
| Developing Institution: | The Johns Hopkins University |
| Telescope Optics: | 90-centimeter (36-inch) aperture, f/2 focal ratio, silicon carbide-coated, parabolic mirror |
| Spectrograph: | Prime-focus, Rowland-circle design using a 600 line/mm grating coated with silicon carbide |
| Spectral Resolution: | 3.0 angstroms |
| Wavelength Range: | 825 to 1850 angstroms (first order) |
| 420 to 925 angstroms (second order) | |
| Detector: | photon-counting |
| microchannel-plate intensifier | |
| cesium iodide photocathode | |
| 1024 element photo-diode array detector | |
| Time Resolution: | 1 ms in high time mode |
| 2 s in histogram mode | |
| Dark Count Rate: | 0.001 counts/Angstrom/s |
| Peak Effective Area: | 35 sq. cm at 1200 angstroms |
| Sensitivity: | S/N of 10 per Angstrom in 1800 s for Flambda=3.3e-14 ergs/cm2/s/A |
| Weight: | 789 kilograms (1736 pounds) |
| Dimensions: | 1.1 meter (4 feet) diameter |
| 3.7 meters (12 feet) length | |
| Field of View of Guide TV: | 10 arc-minutes |
The Hopkins Ultraviolet Telescope (HUT) was designed and built by members of the Center for Astrophysical Sciences and the Applied Physics Laboratory of The Johns Hopkins University in Baltimore, Maryland. HUT consists of a 90-centimeter (36-inch) f/2 mirror that focuses light from celestial sources onto a prime focus spectrograph.
Covering the 825-1850-angstrom region with about 3-angstrom resolution, HUT opened the astrophysically important 912 to 1200-angstrom window to detailed scrutiny for the first time. In typical 1800 s integrations, HUT observed faint astronomical objects with visual magnitudes of about 16.
Originally designed to explore the far- and extreme-ultraviolet ranges on Astro-1, HUT was modified for Astro-2 to concentrate on the far-ultraviolet. The changes made to HUT for Astro-2 included a new detector system and new silicon carbide coatings on the mirror and grating which replaced the original iridium and osmium. These improvements provided a factor of 2.3 increase in sensitivity in the primary operating range of 825 to 1850 angstroms, especially in the 912- to 1200-angstrom region unique to HUT.
HUT Observations of the Intergalactic Medium
The HUT science team's highest priority science goal on Astro-2 was to detect and measure the characteristics of the primordial intergalactic medium (IGM), a hypothesized gas thought to be spread throughout the Universe between the galaxies. This gas should have been created in the Big Bang and then condensed to form the galaxies and stars we see today. The observation required multiple observations of a faint, high redshift quasar, using it as a "background" source to shine through the IGM; absorption of the quasar's light at the "right" ultraviolet wavelengths would indicate the presence of this elusive component of the Universe.
Astronomers have long been interested in observing the IGM directly, as it forms a key link in the chain of events leading from the origin of the Universe to its present-day structure. This project was one of the original motivations for building HUT back when it was proposed to NASA in 1978. An initial attempt to make the required observations was performed during Astro-1, but pointing problems and other operational difficulties caused the program to be abandoned at that time.
Before Astro-2, the IGM apparently was detected for the first time using the Hubble Space Telescope! These observations were very exciting, but were made using quasars of such high redshift that the quasars' light was completely absorbed--the IGM was present, but its characteristics could not be determined. The strength of HUT was that it could observe to shorter wavelengths, and therefore look for signs of the IGM in lower redshift objects where the absorption would not be so strong. This would allow not only the detection of the IGM along a different line of sight, but also permit us to learn about the amount of material involved and what its ionization state was, key clues to this important "missing link" in the evolution of the Universe.
The improved sensitivity of HUT and the stable pointing of the Spacelab IPS on Astro-2, combined with some "luck" provided by Mother Nature, allowed us to make an excellent measurement of the IGM. HUT expended some 12 shuttle pointings (almost 20,000 seconds of observation) on the best quasar candidate for this program, a quasar known as HS 1700+64, which is at a redshift of 2.74. The HUT data show an absorption at just the expected range of wavelengths to be due to the expected effects of the IGM. Furthermore, the spectrum does not drop to zero, as do the Hubble QSO spectra, but hovers in an intermediate range that allows the properties of the IGM to be investigated. Analysis of the HUT spectrum shows that the quasars at high redshift are the likely source of the ionization of material in the IGM, and that there is roughly 4-6 times more mass of "normal" (called "baryonic") material in the IGM than there is in all of the known stars and galaxies combined! While this is not nearly enough material to "close" the Universe or account for the so-called "missing mass" in clusters of galaxies and elsewhere, it does say that only something like 20% of the material created in the Big Bang actually coalesced into the "structure" (galaxies and stars) that we see in the Universe today. The rest of it is "out there" between the galaxies in the form of the exceedingly tenuous intergalactic medium. Now there's a "far out" result!
Scientific Results
The Astro-2 Mission has exceeded the most optimistic expectations held for it by members of the Hopkins Ultraviolet Telescope team. Based on the quantity and quality of the unique new scientific data gathered on this flight, as evaluated with the quick-look data available to us in the Payload Operations Control Center in real time, Astro-2 must be judged an unqualified scientific success.
More than 200 separate successful observations were made of objects selected by HUT investigators, including studies of more than 100 different objects. All of these observations will contribute to answering the questions posed by 14 PI team science programs and 7 guest investigator programs. The observations made with HUT form a unique set of spectrophotometric data in the far ultraviolet band of the electromagnetic spectrum, providing information that has never been obtained previously, and for which no other telescopes are suitable. These data are highly complementary to related data obtained at longer wavelengths with the spectrographs aboard the Hubble Space Telescope.
In the 18 months since the Astro-1 mission, analysis of the data obtained with HUT has provided us with new insights into topics in particle physics, cosmology, active galactic nuclei, quasars, normal galaxies, the interstellar medium, stellar astrophysics, and the solar system. A few of the interesting results that have been derived so far are summarized in the following from Science, 1993, 259, 327.
- The Galactic Corona
- The Local Interstellar Medium
- Origin of Ultraviolet Light in Elliptical Galaxies
- Seyfert Galaxies
- Other Results from HUT
- Future Work and Astro-2
A summary of some of the observation highlights can be found in the End of Mission Report for the HUT.
References
- End of Mission PAO Report for the Hopkins Ultraviolet Telescope - Center for Astrophysical Sciences, The Johns Hopkins University.
- Far-Ultraviolet Astronomy on the Astro-1 Space Shuttle Misssion - Center for Astrophysical Sciences, The Johns Hopkins University.
- Hopkins Ultraviolet Telescope Project - Center for Astrophysical Sciences, The Johns Hopkins University.
- HUT Observations of the Intergalactic Medium - Hopkins Ultraviolet Telescope Project, Center for Astrophysical Sciences, The Johns Hopkins University.
External Links
- ASTRO-1 mission - NASA
- ASTRO-2 mission - NASA
- Hopkins Ultraviolet Telescope (HUT) Description - NASA
- Hopkins Ultraviolet Telescope Handbook - Center for Astrophysical Sciences, The Johns Hopkins University.
- HUT Quick Look Spectral Atlases for Astro-1 and Astro-2 - Center for Astrophysical Sciences, The Johns Hopkins University.
Further Reading
- The technical report of the HUT research findings can be found in an article by A. F. Davidsen, G. A. Kriss, and W. Zheng in the journal Nature, vol. 380, p. 47 (1996).
- Far-Ultraviolet Astronomy on the Astro-1 Space Shuttle Mission - Published in Science 15 January 1993: Vol. 259. no. 5093, pp. 327 - 334.
- HUT Papers from the Astro-1 Mission.
- HUT Papers from the Astro-2 Mission.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Center for Astrophysical Sciences, The Johns Hopkins University. Topic editors and authors for the Encyclopedia of the Cosmos may have edited its content or added new information. The use of information from the Center for Astrophysical Sciences, The Johns Hopkins University should not be construed as support for, or endorsement by, that organization for any new information added by EoC personnel, or for any editing of the original content.
Original content retrieved from articles listed in References above.
Citation
Haisch, Bernard, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Hopkins Ultraviolet Telescope." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 24, 2007].
<http://www.cosmosportal.org/articles/view/135719/>
Contact Us
Send to a Friend
Comments
There are no comments.