Current Performance of Ground-Based Interferometers

Here is a list of currently existing astronomical optical interferometers (i.e. operating from visible to mid-infrared wavelengths), and some parameters describing their performance.

Columns 2-5 determine the range of targets that can be observed and the range of science which can be done. Higher limiting magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 means that the array can observe fainter sources (and the most interesting sources are often very faint). The limiting magnitude is determined by the atmospheric seeing

Astronomical seeing

Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...

, the diameters of the telescopes and the light lost in the system. A larger range of baselines means that a wider variety of science can be done and on a wider range of sources.

Columns 6-10 indicate the approximate quality and total amount of science data the array is expected to obtain. This is per year, to account for the average number of cloud-free nights on which each array is operated.

Current Performance of Existing Astronomical Interferometers

Interferometer and observing mode	Waveband	Limiting magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...	Minimum baseline (m) (un-projected)	Maximum baseline (m)	Approx. no. visibility measurements per year (measurements per night x nights used per year)	Max ratio of no. phase / no. amplitude measurements (measure of imaging performance, 0 = none)	Accuracy of amplitude2 measurements	Accuracy of phase measurements (milli-radians)	Number of spectral channels (max in use simultaneously)	Comments
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...	V, R, I, J, H, K	8	34	330	7500	0.7	1%	10	30000	Yes... 30000 in the visible band
COAST visible	R, I	7	4	60	2000	0.5	4%	10	4?	300 cloudy nights per year
COAST infrared	J, H	3	4	60	100	0.5	20%	10	1	300 cloudy nights per year
GI2T Grand Interferometre a 2 Telescopes The Grand Interferometre a 2 Telescopes is an Optical Interferometer, on Plateau du Calern, Departement Fresnel, Observatoire de la Côte d'Azur, France. The observatory was closed in 2006. - External links :* on the internet...  visible	R, I	5	10	65	2000	0	10%	-	400?	Closed in 2006
IOTA Infrared Optical Telescope Array The Infrared Optical Telescope Array began with an agreement in 1988 among five Institutions, the Smithsonian Astrophysical Observatory, Harvard University, the University of Massachusetts, the University of Wyoming, and MIT/Lincoln Laboratory, to build a two-telescope stellar interferometer for...	J, H, K	7	6	30	10000	0.3	2%	10	1?	Integrated optics beam combiner
ISI Infrared Spatial Interferometer The Infrared Spatial Interferometer is an astronomical interferometer array of three 65 inch telescopes operating in the mid-infrared. The telescopes are fully mobile and their current site on Mount Wilson allows for placements as far as 70 m apart, giving the resolution of a telescope of that...	N	0	10	50	5000	0.3	1%	1	1000
Keck Interferometer	H, K, L, N	10.3	85	85	1000	0	4%	1	330	Nulling Key Science Underway - No imaging on a single baseline instrument
Keck Aperture Masking Aperture masking interferometry Aperture Masking Interferometry is a form of speckle interferometry, allowing diffraction limited imaging from ground-based telescopes. This technique allows ground based telescopes to reach the maximum possible resolution, allowing ground-based telescopes with large diameters to produce far...	J, H, K, L	2	0.5	9	20000	0.9	20%	10	1
MIRA 1.2	R, I	3	30	30	500	0	10%	-	1
Navy Prototype Optical Interferometer Navy Prototype Optical Interferometer The Navy Prototype Optical Interferometer , is an astronomical interferometer operated by the United States Naval Observatory Flagstaff Station, in collaboration with the Naval Research Laboratory and The Lowell Observatory... (NPOI) visible	V, R, I	5	5	300	50000	0.7	4%	10	16	at NOFS 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,... ; pending 4 x 1.8m added apertures
Palomar Testbed Interferometer Palomar Testbed Interferometer The Palomar Testbed Interferometer was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer...	J,H,K	7	86	110	50000	0	2%	0.1	5,10	"dual-star" capable , No imaging on a single baseline instrument. Closed 2009.
SUSI	B, V, R, I	5	5	640	5000	0	4%	10	?	No imaging on a single baseline instrument
VLTI VLT VLT may stand for:* Very Large Telescope, a system of four large optical telescopes organized in an array formation, located in northern Chile... +UTs AMBER	J, H, K simultaneously	7	46	130	400	0.3	1%	10	2000	Used for a few weeks per year
VLTI +ATs AMBER	J, H, K simultaneously	4	46	130	400	0.3	1%	10	2000
VLTI +UTs VINCI	K	11	46	130	400	0	>1%	-	1	Integrated optics beam combiner
VLTI +ATs VINCI	K	Never checked	12	200	400	0	>1%	-	1
VLTI +UTs MIDI	N	4.5	46	130	200	0	10%	-	250	Used for a few weeks per year
VLTI +ATs MIDI	N	4.5	?	200	200	0	10%	-	250

New Interferometers and Improvements to Existing Interferometers

Expected Future Performance of Astronomical Interferometers

Interferometer and observing mode	Waveband	Limiting magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...	Minimum baseline (m) (un-projected)	Maximum baseline (m)	Approx. no. visibility measurements per year (measurements per night x nights used per year)	Max ratio of no. phase / no. amplitude measurements (measure of imaging performance, 0 = none)	Accuracy of amplitude2 measurements	Accuracy of phase measurements (milli-radians)	Number of spectral channels (max in use simultaneously)	Comments
LBTI Large Binocular Telescope Large Binocular Telescope is an optical telescope for astronomy located on Mount Graham in the Pinaleno Mountains of southeastern Arizona, and is a part of the Mount Graham International Observatory... (near infrared)	J, H, K	>20	0	22	10000000	1	30%	100	100?	2006?
MRO	R, I, J, H, K	14	7	400	100000	0.6	1%	10	1000?	Under Construction
VLTI Very Large Telescope The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to... (near infrared using 4 ATs and PRIMA)	J, H, K	12	8	200	10000	1	1%	0.1	4000?	Operating every night 2008?
VLTI Very Large Telescope The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to... (near infrared using 3 UTs and PRIMA)	J, H, K	14	46	130	500	1	1%	0.3	4000?	2008?