# List of astronomical interferometers at visible and infrared wavelengths

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.

## Current performance of ground-based interferometers

Columns 2-5 determine the range of targets that can be observed and the range of science which can be done. Higher limiting magnitude means that the array can observe fainter sources. The limiting magnitude is determined by the atmospheric seeing, 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 | 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 amplitude$^2$ measurements | Accuracy of phase measurements (milli-radians) | Number of spectral channels (max in use simultaneously) | Operational? | Comments |
| CHARA Array | V, R, I, J, H, K | 8 | 34 | 330 | 7500 | 0.7 | 1% | 10 | 30000 | Yes | 30000 in the visible band; maximum baseline 330-m |
| COAST visible | R, I | 7 | 4 | 60 | 2000 | 0.5 | 4% | 10 | 4? | Closed | 300 cloudy nights per year, maximum baseline 100-m |
| COAST infrared | J, H | 3 | 4 | 60 | 100 | 0.5 | 20% | 10 | 1 | Closed | 300 cloudy nights per year, maximum baseline 100-m |
| GI2T visible | R, I | 5 | 10 | 65 | 2000 | 0 | 10% | - | 400? | Closed | CLOSED in 2006 |
| IOTA | J, H, K, L' | 7 | 6 | 30 | 10000 | 0.3 | 2% | 10 | 1? | Closed | Integrated optics beam combiner. CLOSED. |
| ISI | N | 0 | 10 | 50 | 5000 | 0.3 | 1% | 1 | 1000 | Closed | Maximum baseline 70-m |
| Keck Interferometer | H, K, L, N | 10.3 | 85 | 85 | 1000 | 0 | 4% | 1 | 330 | Closed | Nulling Key Science Underway - No imaging on a single baseline instrument; maximum baseline 11-m. CLOSED. |
| Keck Aperture Masking | J, H, K, L | 2 | 0.5 | 9 | 20000 | 0.9 | 20% | 10 | 1 | | CLOSED. |
| MIRA 1.2 | R, I | 3 | 30 | 30 | 500 | 0 | 10% | - | 1 | Closed | Mid-Infrared |
| Navy Precision Optical Interferometer(NPOI) | V, R, I | 6 | 5 | 97 (operational) 432 (not yet commissioned) | 50000 | 0.7 | 4% | 10 | 16 | Yes | at Lowell Observatory 12cm siderostats operational 3 x 1.0m apertures being added World's largest optical baseline-437m 6-phased |
| Palomar Testbed Interferometer | J,H,K | 7 | 86 | 110 | 50000 | 0 | 2% | 0.1 | 5,10 | Closed | "dual-star" capable , No imaging on a single baseline instrument. CLOSED 2009. |
| SUSI | B, V, R, I | 5 | 5 | 160 (operated) 640 (never commissioned) | 5000 | 0 | 4% | 10 | 21 | Closed | No imaging on a single baseline instrument; Maximum baseline 160m |
| VLTI +UTs AMBER | J, H, K simultaneously | 7 | 46 | 130 | 400 | 0.3 | 1% | 10 | 2000 | Yes | Used for a few weeks per year. Longest overall VLTI Baseline 130m |
| VLTI +ATs AMBER | J, H, K simultaneously | 4 | 46 | 130 | 400 | 0.3 | 1% | 10 | 2000 | Yes | Longest overall VLTI Baseline 130m |
| VLTI +UTs VINCI | K | 11 | 46 | 130 | 400 | 0 | >1% | - | 1 | Yes | Integrated optics beam combiner. Longest overall VLTI Baseline 130m |
| VLTI +ATs VINCI | K | Never checked | 12 | 200 | 400 | 0 | >1% | - | 1 | Yes | Longest overall VLTI Baseline 130m. |
| VLTI +UTs MIDI | N | 4.5 | 46 | 130 | 200 | 0 | 10% | - | 250 | Yes | Used for a few weeks per year. Longest overall VLTI Baseline 130m. Dismantled Apr 2015 |
| VLTI +ATs MIDI | N | 4.5 | ? | 200 | 200 | 0 | 10% | - | 250 | Yes | VLTI inldes World's largest unfilled apertures (siderostats, 1.8-m, 8-m). Longest overall VLTI Baseline 130m. Dismantled Apr 2015 |

## New interferometers and improvements to existing interferometers

Expected Future Performance of Astronomical Interferometers :
| Interferometer and observing mode | Waveband | Limiting magnitude | 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 amplitude$^2$ measurements | Accuracy of phase measurements (milli-radians) | Number of spectral channels (max in use simultaneously) | Comments |
| LBTI (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 (near infrared using 4 ATs and PRIMA) | J, H, K | 12 | 8 | 200 | 10000 | 1 | 1% | 0.1 | 4000? | decommissioned 2014 |
| VLTI (near infrared using 3 UTs and PRIMA) | J, H, K | 14 | 46 | 130 | 500 | 1 | 1% | 0.3 | 4000? | decommissioned 2014 |
| VLTI (near infrared using 4 UTs and MATISSE) | J, H, K, N, Q | | | | | | | | | commissioning 2017? |