Green Bank Interferometer
{{Short description|Former radio telescope in Green Bank, West Virginia}}
{{Infobox Telescope
| locmapin = West Virginia
}}
The Green Bank Interferometer (GBI) is a former radio astronomy telescope located at Green Bank, West Virginia, U.S., and operated by the National Radio Astronomy Observatory. It included three on-site radio telescopes of 85-foot (26m) diameter, designated 85-1, 85-3, and 85-2 (85-1 is also known as the Tatel Telescope) and a portable telescope.
History
File:Howard E. Tatel Radio Telescope - front.jpg
The first telescope (85-1, Tatel) was built in 1959 at a fixed location. It was used in Project Ozma in 1960 without interferometer. In 1963, in anticipation of adding movable telescopes for the interferometer, the second {{Convert|85|ft|m|adj=on}} telescope kit identical to 85-1 was ordered. The construction of the second telescope (85-2) was completed in 1964 along with a {{Convert|1.5|mi|km|adj=on}} track from 85-1. At that time, the 85-2 telescope was placed at the end of the track and cables were connected between the two telescopes. The GBI began operation that year as a two element interferometer in order to test large aperture synthesis arrays and study radio astrometry and interstellar scintillation.
File:85-3 Radio Telescope at Green Bank NRAO.jpg
In 1967 the array was upgraded with construction of the third element (85-3) to be located in the middle of the track. Both 85-2 and 85-3 had truck tires mounted on either side to allow them to be moved along the track to test different baselines. The limitation of the 3-element interferometer along a short track became apparent. A {{Convert|42|ft|m|adj=on}} portable telescope was procured. The portable telescope was placed {{Convert|8|mi|km}} away from Green Bank site and then moved to {{Convert|11|mi|km}} forming a T shape with the length of the bottom arm of the T to be similar to the length of each arm of the Y configuration at Karl G. Jansky Very Large Array (VLA) which was still in a design phase. The portable telescope was later placed on a mountaintop in Huntersville, West Virginia, {{Convert|26|mi|km}} away from Green Bank, which is the same distance of the longest baseline of VLA. The portable telescope was replaced in 1973 with {{Convert|45|ft|m|adj=on}} portable telescope which was in use until 1983.{{cite web|title=Green Bank Interferometer|url=https://public.nrao.edu/telescopes/historic/green-bank-interferometer|access-date=2 November 2016}}
File:Green Bank 45-foot Radio Telescope.jpg
From 1978-1996, the GBI was operated in support of USNO and NRL geodetic and astronomy programs. In 1979, the GBI configuration had 85-3 and 85-2 at {{Convert|0.9|mi|km}} and {{Convert|1.5|mi|km}} away from 85-1 respectively, and the portable telescope at {{Convert|22|mi|km}} from Green Bank.{{cite journal|last1=Klepczynski|first1=W. J.|last2=Kaplan|first2=G. H.|last3=McCarthy|first3=D. D.|last4=Josties|first4=F. J.|last5=Branham|first5=R. L.|last6=Johnston|first6=K. J.|last7=Spencer|first7=J. S.|title=Progress Report on The USNO/NRL Green Bank Interferometer Program|journal=NASA Conference Publication 2115: Radio Interferometry Techniques for Geodesy|date=1980|page=63|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800020297.pdf|access-date=2 November 2016}} In 1983, the {{Convert|45|ft|m|adj=on}} portable telescope was moved back to Green Bank for another function to become a tracking station for Space VLBI satellites. The new {{Convert|46|ft|m|adj=on}} portable telescope was put in place for interferometer operation until 1988 when the GBI reconfigured to 2-element interferometer with 85-3 taken out to become geodetic VLBI and pulsar monitoring telescope.{{cite web|title=NRAO-GBI previous operations|url=http://www.gb.nrao.edu/fgdocs/gbi/gbiolder.html|publisher=The National Radio Astronomy Observatory|access-date=2 November 2016}}
The GBI resumed operation as a radio monitoring instrument on Nov. 22, 1996, operated by NRAO and supported by the NASA High Energy Astrophysics program. The GBI was then used as a two telescope interferometer that operated simultaneously at 2.25 and 8.3 GHz to monitor transient, galactic X-ray binaries, AGN's and Gamma-ray sources. Amongst the prime sources were GRS 1915+105, GRO J1655-40, Cyg X-3, Cyg X-1, GRS 1716-249, SS 433, and LS I +61 303.{{cite journal|last1=Hjellming|first1=R. M.|last2=Waltman|first2=E. B.|last3=Ghigo|first3=F.|title=Radio Light Curves of X-ray Sources Obtained with the Green Bank Interferometer|journal=American Astronomical Society, 191st AAS Meeting, Id.110.17; Bulletin of the American Astronomical Society|date=December 1997|volume=29|pages=110.17|bibcode=1997AAS...19111017H}}
On October 6, 2000 the GBI monitoring program has ceased due to lack of funding.{{cite web|url=http://www.gb.nrao.edu/fgdocs/gbi/gbint.html|title=NRAO Green Bank Interferometer|website=www.gb.nrao.edu}}
Technical Data: 2-element interferometer
- Baseline: 2400 meters at an azimuth of 62 degrees (E of N).
- Bands: 8.3 GHz (X-band) and 2.25 GHz (S-band) with 35 MHz bandwidth.
- Receivers: Cryogenically cooled, dual frequency, dual polarization. Both X and S bands simultaneously observed in both right and left circular polarizations.
- System temperature: About 35 K in Sband and 45 K in Xband.
- Sensitivity: RMS noise in a 5-minute scan is about 6 mJy in S-band and 10 mJy in X-band for point sources.
- Minimum integration time: 30 seconds.
- Resolution: About 3 arcseconds fringe at X-band and 11 arcseconds at S-band.
See also
References
{{reflist}}
External links
- {{Commons category inline}}
- [http://www.gb.nrao.edu/fgdocs/gbi/gbint.html Green Bank Interferometer home page]
{{Radio-telescope}}
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Category:Astronomical observatories in West Virginia
Category:Buildings and structures in Pocahontas County, West Virginia