Navy Prototype Optical Interferometer
| Navy Optical Interferometer | |
Navy Optical Interferometer
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| Organization | USNO, NRL, Lowell |
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| Location | near Flagstaff, Arizona |
| Coordinates | 35°05′45″N 111°32′02″W / 35.0959°N 111.5339°WCoordinates: 35°05′45″N 111°32′02″W / 35.0959°N 111.5339°W |
| Altitude | 2,163 meters (7,096 ft) |
| Wavelength | Optical/Near-infrared |
| Built | 1992 |
| First light | 1994 |
| Telescope style | Interferometer |
| Website | Navy Optical Interferometer |
 Related media on Wikimedia Commons |
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The Navy Optical Interferometer (NOI) is an astronomical interferometer operated by the United States Naval Observatory Flagstaff Station (NOFS) in collaboration with the Naval Research Laboratory (NRL) and Lowell Observatory. The facility is located at Lowell's Anderson Mesa Station on Anderson Mesa about 25 kilometers (16 mi) southeast of Flagstaff, Arizona (USA). Until November 2011, the facility was known as the Navy Prototype Optical Interferometer (NPOI), at which point it was renamed the Navy Optical Interferometer (NOI), reflecting the operational maturity of the facility.[1]
The NPOI project was initiated by the United States Naval Observatory (USNO) in 1987.[2] Lowell joined the project the following year when the USNO decided to build the NPOI at Anderson Mesa.[3] The first phase of construction was completed in 1994, which allowed the interferometer to see its first fringes, or light combined from multiple sources, that year.[4] Regular science operations began in 1997.[5] The NOI has been continuously upgraded and expanded since then.
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[edit] Description
The NOI is laid out in a three-arm configuration, with each equally-spaced arm measuring 250 meters (820 ft) long. There are two types of stations that can be used in the NOI. Astrometric stations, used to measure the positions of stars very accurately, are fixed units placed 21 meters (69 ft) apart, with one on each arm and one at the center. Imaging stations can be moved to one of nine positions on each arm, and up to six can be used at one time to perform standard observing. Light from either type of station is first directed into the feed system, which consists of long pipes which have been evacuated of all air. They lead to a switchyard of mirrors, where the light is directed into the six Long Delay Lines, which is another set of long pipes that compensate for the different distances to each station. The light is then sent into the Beam Combining Facility, where it enters the Fast Delay Lines. This third set of evacuated pipes contains mechanisms that move mirrors back and forth with a very high degree of accuracy. These compensate for the movement of the mirrors as they track an object across the sky, and for other effects. Finally, the light leaves the pipes inside the BCF and goes to the Beam Combining Table, where the light is combined in a way that allows images to be formed.[2]
Both types of station have three elements: a siderostat, a Wide Angle Star Aquisition (WASA) camera, and a Narrow Angle Tracking (NAT) camera. The first is a precisely-ground flat mirror 50 cm (20 in) in diameter. The WASA cameras control the aiming of the mirror at the celestial target. The reflected light from the siderostat is directed through a telescope which narrows the beam down to the diameter of the pipes, which is 12 cm (4.7 in). The light then hits the mirror of the NAT, which compensates for atmospheric effects and directs the light into the feed system.[2]
In 2008 NOI began plans to incorporate four 1.8 m (71 in) aperture optical-infrared telescopes into the array.[6] They were originally intended to be "outrigger" telescopes for the W. M. Keck Observatory in Hawaii, but were never installed and incorporated into Keck's interferometer. In November 2010, the telescopes were accepted, and three are expected to come online in 2012.[7][8] The fourth is currently at Siding Spring Observatory in Australia and will be incorporated at some point in the future.[6] The new telescopes will help with faint object imaging due to their greater light-gathering abilities than the existing siderostats.[6]
[edit] Discussion
Optical interferometers are extremely complex, unfilled aperture photon-collecting telescopes in the visual (sometimes the near infrared, too), which produce synthesized images and fringe data "on the fly" (unlike radio interferometers which are privileged to record the data for later synthesis), essentially by taking an inverse Fourier transform of the incoming data. Astrometry is understood by precisely measuring delay line additions while fringing, to match the light path differences from baseline ends. Using essentially trigonometry the angle and position of where the array is 'pointed' can be determined, thus inferring a precise position on the sphere of the sky.
Only a few exist, that can be considered operational. To date NOI has produced the highest resolution optical images of any astronomical instrument, though this may change when the CHARA array and Magdalena Ridge Observatory Interferometer begin optical-band operations.[9] The first astronomical object imaged (resolved) by NOI was Mizar, and since, a significant amount of astrometry, reference tie frame, rapid rotator star, and Be stellar disk study has been performed.[10] NOI is capable of determining positions of celestial objects to a few milli-arcsecond, in part due to the optical anchoring of its components using a complex metrology array of lasers that connect main optical elements to each other and to bedrock.
Many specialized lasers are also used to align the long train of optics. The current NOI siderostat array remains the world's only long-baseline (437-meter) optical interferometer that can simultaneously co-phase six elements.[11] NOI is expected to grow significantly in capability with the pending addition of four 1.8-meter aperture IR/Optical telescopes into the current array.[6] The enhanced array will also employ adaptive optics techniques. This layout and increased sparse aperture will permit significant improvements to the science capability, from a tenfold increase in measuring ever-fainter wide-angle astrometry targets, to improved positional determination for numerous binary and flare stars. When the 1.8m telescope addition are complete, NOI also will undertake additional studies of dust and proto-planetary disks, and planetary systems and their formation.[12]
[edit] See also
[edit] References
- ^ "NPOI renamed to reflect its evolving role in research". Lowell Observatory. http://www.lowell.edu/news/2011/11/npoi-renamed-to-reflect-its-evolving-role-in-research/. Retrieved 2012-01-04.
- ^ a b c Armstrong, J. T.; Mozurkewich, D.; Rickard, L. J.; Hutter, D. J.; Benson, J. A.; Bowers, P. F.; Elias, N. M.; Hummel, C. A. et al (1998). "The Navy Prototype Optical Interferometer". Astrophysical Journal v.496 496: 550. Bibcode 1998ApJ...496..550A. doi:10.1086/305365.
- ^ Hutter, D. J.; Elias, N. M.; Peterson, E. R.; Weaver, W. B.; Weaver, G.; Mozurkewich, D.; Vrba, F. J.; Simon, R. S. et al (1997). "Seeing Tests at Four Sites in Support of the NPOI Project". Astronomical Journal v.114 114: 2822. Bibcode 1997AJ....114.2822H. doi:10.1086/118690.
- ^ Hutter, Donald J. (1995). "Current Status of the Navy Prototype Optical Interferometer". American Astronomical Society 187: 1452. Bibcode 1995AAS...18712102H.
- ^ Armstrong, J. T.; Mozurkewich, D.; Pauls, T. A.; Rickard, L. J.; Benson, J. A.; Dyck, H. M.; Elias, N. M.; Hajian, A. R. et al (1997). "The Navy Prototype Optical Interferometer (NPOI) is Operational". American Astronomical Society 191: 1234. Bibcode 1997AAS...191.1603A.
- ^ a b c d Divittorio, Michael; Hutter, Donald J.; Kelley, Michael (2008). "Plans for utilizing the Keck Outrigger Telescopes at NPOI". Optical and Infrared Interferometry. Edited by Schöller 7013: 87. Bibcode 2008SPIE.7013E..87D. doi:10.1117/12.787635.
- ^ "Acceptance of Gift of Telescopes". United States Navy. 2010-11-03. http://www.nofs.navy.mil/about_NOFS/telescopes/LTRs_1.8m_UNSECNAV_Accept.pdf. Retrieved 2012-01-04.
- ^ Hutter, Don (2011-03-01). "NPOI Update". United States Naval Observatory. http://www.chara.gsu.edu/CHARA/Papers/Atlanta/Hutter.pdf. Retrieved 2012-01-05.
- ^ Armstrong, J. T. (2004). "Precision narrow-angle astrometry of binary stars with the Navy Prototype Optical Interferometer". Proceedings of SPIE. 5491. pp. 1700. doi:10.1117/12.553062.
- ^ "The U.S. Naval Observatory Preprint Library (2011)". United States Naval Observatory. 2011-03-01. http://ad.usno.navy.mil/edboard/preprints.html. Retrieved 2012-01-05.
- ^ Hutter, Donald J.; Benson, James A.; Buschmann, Tim; Divittorio, Michael; Zavala, Robert T.; Johnston, Kenneth J.; Armstrong, J. Thomas; Hindsley, Robert B. et al (2008). "NPOI: recent progress and future prospects". Proceedings of SPIE. 7013. pp. 701306. doi:10.1117/12.787486.
- ^ Shankland, Paul D.; Divittorio, M. E.; Hutter, D. J.; Benson, J. A.; Zavala, R. T.; Johnston, K. J. (2010). "The Science with Four 1.8-m Telescopes at the Navy Prototype Optical Interferometer". American Astronomical Society 215: 402. Bibcode 2010AAS...21544112S.
