Navy Prototype Optical Interferometer
Encyclopedia
The Navy Prototype Optical Interferometer (NPOI -- note recently the 'Protoype' was dropped so that the facility is now called "NOI"), is an astronomical interferometer
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....

  operated by the United States Naval Observatory Flagstaff Station
United States Naval Observatory Flagstaff Station
The United States Naval Observatory Flagstaff Station , is a scientific astronomical observatory operated as a Navy Echelon V command and the national dark-sky observing Facility/observatory subordinate to the United States Naval Observatory . USNO and NOFS are commands within the CNMOC claimancy,...

, in collaboration with the Naval Research Laboratory and The Lowell Observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....

. The facility is located on Anderson Mesa
Anderson Mesa
Lowell Observatory, Anderson Mesa Station, USA, was established in 1959 as a dark-sky observing site for Lowell Observatory. Anderson Mesa is now home to several large reflecting telescopes that are used for observing programs such as LONEOS...

 about 15 miles southeast of Flagstaff, Arizona
Flagstaff, Arizona
Flagstaff is a city located in northern Arizona, in the southwestern United States. In 2010, the city's population was 65,870. The population of the Metropolitan Statistical Area was at 134,421 in 2010. It is the county seat of Coconino County...

. More information on how NOI works can be found at the new NPOI webpage . In 2009 NOI began to finalize the acceptance of four, 1.8m aperture optical-infrared telescopes to include in the array, and tremendously increase its fainter-star performance. In November 2010, acceptance was complete, and procedures have been undertaken to install the four telescopes into the existing Y-shaped array.

Optical interferometers are extremely complex, unfilled aperture photon-collecting telescopes in the visual (sometimes the near infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

, 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
Trigonometry
Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

 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 (this may change if/when the CHARA array
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...

 and Magdalena Ridge Observatory Interferometer begin optical-band operations). The first astronomical object imaged (resolved) by NOI was Mizar
Mizar (star)
The Mizar–Alcor stellar sextuple system consists of the quadruple system Mizar and the binary system Alcor.- Description :Mizar is a quadruple system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23...

, and since, a significant amount of astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...

, reference tie frame, rapid rotator star, and Be stellar disk study has been performed . 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
Metrology
Metrology is the science of measurement. Metrology includes all theoretical and practical aspects of measurement. The word comes from Greek μέτρον , "measure" + "λόγος" , amongst others meaning "speech, oration, discourse, quote, study, calculation, reason"...

 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 . 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 . The enhanced array will also employ adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...

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 additions complete, NOI also will undertake additional studies of dust and protoplanetary disks, and planetary systems and their formation .

External links


External links

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