NPOI - Naval Prototype Optical Interferometer  
Naval Prototype Optical Interferometer U.S. Naval Observatory Naval Prototype Optical Interferometer Naval Research Laboratory Naval Prototype Optical Interferometer Lowell Observatory
Naval Prototype Optical Interferometer Naval Prototype Optical Interferometer Naval Prototype Optical Interferometer Naval Prototype Optical Interferometer Naval Prototype Optical Interferometer
U.S. Naval Observatory Naval Research Laboratory
Lowell Observatory
A Brief History of the NPOI

March:  Positive fringe detection of a geostationary satellite on 2 nights.

January:  Position precisions of 16 milliarcseconds demonstrated for 58 stars towards the first USNO-NPOI Astrometric Catalog (UNAC).

October:  First orbit of close pair in Algol triple star system from optical interferometry; orbit of outer star corrected.

>>>(Figure from Bob Z here)<<<<<

April:  Record nightly number of multi-baseline observations: 282.

March:  Record monthly number of observations: 4,343.

February:  Tentative fringe detection of a geostationary satellite.

New orbit published for the O-star binary system 1 Orionis C (Patience et al. 2008).

November:  Routine observations commence towards the first “100-star” installment of the NPOI wide-angle astrometric star catalog (UNAC).

March:  White paper on potential science using the NPOI, as enhanced with four 1.8m “outrigger” telescopes.

October:  Simultaneous imaging observations of Algol conducted by NPOI (optical) and Very Long Baseline Interferometry (radio), with supporting spectroscopic observations at Lowell Observatory.

The contours in this image show the close binary in Algol resolved with the NPOI. The grey-scale is a 4cm radio image made from data obtained with the Very Large Array of the National Radio Astronomy Observatory. The shape of the grey-scale represents the changing radio emission as the radio emitting secondary star moves along its orbit during the period of observation. The oval in the lower right represents the resolution of the NPOI array during the observation.

April:  Results of NPOI observations of Vega, published in Nature (Peterson et al. 2006), show this to be a rapidly rotating star (93 percent breakup velocity) seen nearly pole-on.

January:  C-term metrology system operational – greatly improves precision of wide-angle astrometry.

March:  Begin NPOI survey observations of bright stars.

June:  First paper on NPOI observations of the disks of Be stars utilizing self-calibration of the H-alpha channel (Tycner et al. 2003).

May:  First images of triple star system Eta Virginis, based on 6-station observations, published (Hummel et at. 2003).

Images of Eta Vir on 2002 Feb 15 (left) and 2002 May 19 (right).

January:  First routine co-phased 6-station observations – world first.

May:  All Long Delay Line (LDL) vacuum pipes and stations installed.

Begin first observations of Be stars.

March:  Orbit for the close binary star Omicron Leonis published (Hummel et al. 2001).

December:  Sixth siderostat station completed.

September:  NPOI’s resolution of a 4th magnitude companion to the bright (2nd magnitude) star Zeta Orionis A is published (Hummel et al. 2000).

April:  Upgrades of beam combiner to 6-beam combination completed.

Avalanche Photodiode (APD) fringe detectors in new vacuum housings.

Last Fast Delay Line (FDL) installed.

December:  Angular diameters for 50 stars, with precisions of ~1% published (Nordgren et al. 1999)

October:  Start expansion of baseline metrology to last (north) astrometric station. The system at each astrometric hut consists of laser interferometers that measure the position of the siderostat relative to the bedrock under each hut.

November:  Assembly work begins on vacuum and optical systems for the outer array. The photo shows the installation of the vacuum cover over the feed optics at one of the stations on the east arm of the array

July:  Infrared beam-combiner optics installed; first infrared fringes recorded.

June:  First two imaging siderostats installed on the array.

March:  Limb-darkened angular diameters published (Hajian et al. 1998).

September:  Orbit for Mizar published (Benson et al. 1997).

January:  Routine, nightly observing with substantial numbers of observations begins:
Visit a table of calendar year observing statistics for NPOI from 1997 through 2008 .

May:  Concrete work begun for outer part of the array.

March:  First three-baseline observations with closure phase.
The illustration (below) shows that closure phase data may be used to produce real images, here of the binary star Mizar A. The separation between the two stars is about 6.5 milliarcseconds, about eight times the resolution of the Hubble Space Telescope.

October:  First single-baseline stellar fringe observations.

June:  First astrometric telescopes and visible-light beam combiner optics installed.

January:  After approximately a year and a half, the initial phase of construction is completed. This includes the concrete piers to hold the siderostats, beam compressors, elevator cans and center feed cans for the imaging and astrometric arrays, the control and lab buildings, and the astrometric huts.

July:  Control and lab buildings completed, inner array construction begins.

September:  Construction begins on Anderson Mesa.

August:  Culmination of the NEPA process with the issuance of the Decision Notice.

January:  NEPA (National Environmental Policy Act) process initiated.

September:  USNO, NRL, and Lowell Observatory sign a contract to build the NPOI on Lowell’s dark sky site at Anderson Mesa, southeast of Flagstaff, Arizona. Lowell Observatory provides the development site. During the following 12 months, Lowell works with the Forest Service, obtaining the necessary construction permits. Also, sub-contracts were let to local construction firms during this period.

An aerial view of the array site on Anderson Mesa before construction began.
(Place cursor on the image to see the array location.)

July:  Work commences on the project. Funding for what is to become the NPOI is initiated by the Oceanographer of the Navy and the Office of Naval Research. Design work begins on all phases of the project. Fabrication of major components, including the siderostats and the internal components of the elevator and array feed cans and the fast delay lines begins in the USNO instrument shop.

NPOI Calendar Year Observing Statistics:
Multi-Baseline Scan Totals from Monthly Archival Reports

1997      5,978
1998      3,886
1999      1,908
2000      3,158
2001      5,405
2002      9,602
2003      7,680
2004      21,437
2005      13,879
2006      20,803
2007      22,530
2008      23,128
GRAND TOTAL      139,394

U.S. Naval Observatory Naval Research Laboratory Lowell Observatory