Very Long Baseline Array

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Eastern terminus of the VLBA, Saint Croix, U.S. Virgin Islands

The Very Long Baseline Array (VLBA) is a system of ten radio telescopes controlled remotely from the Array Operations Center in Socorro, New Mexico (USA) by the National Radio Astronomy Observatory. The array works together as the world's largest dedicated, full-time astronomical instrument using the technique of very long baseline interferometry. Its construction began in February 1986, and was completed in May 1993. The first observation using all ten sites occurred on May 29, 1993. The total construction cost was US$85 million.

Each VLBA station consists of an 82-foot (25 m) diameter dish antenna and an adjacent control building which houses the station computer, tape recorders and other equipment associated with collecting the radio signals gathered by the antenna. Each antenna weighs 218 tonnes (240 tons) and is nearly as tall as a ten story building when pointed straight up. The longest baseline in the array is 8,611 kilometres (5,351 mi).[1]

The signals from each antenna are recorded and time stamped using precise, synchronized clocks. The individual recordings are dispatched to a central location and then are combined using a correlator to produce the required interferometric signal. Corrections must be applied for the rotation of the Earth, slight shifts in the local clocks, and so forth. The total exposure time is constrained due to phase shifts induced by the Earth's atmosphere.[2]

The VLBA radio telescopes are located at:

Very Long Baseline Array is located in United States
Hancock
North Liberty
Fort Davis
Los Alamos
Pie Town
Kitt Peak
Owens Valley
Brewster
Green Bank
Very Large Array
VLBA locations in contiguous United States
Toponymy U.S. state Geographic coordinate system
St. Croix U.S. Virgin Islands 17°45′23″N 64°35′02″W / 17.75652°N 64.58376°W / 17.75652; -64.58376 SC
Hancock New Hampshire 42°56′01″N 71°59′13″W / 42.93362°N 71.98681°W / 42.93362; -71.98681 HN
North Liberty Iowa 41°46′18″N 91°34′27″W / 41.77165°N 91.574133°W / 41.77165; -91.574133 NL
Fort Davis Texas 30°38′07″N 103°56′41″W / 30.635214°N 103.944826°W / 30.635214; -103.944826 FD
Los Alamos New Mexico 35°46′56″N 106°15′20″W / 35.78233°N 106.25568°W / 35.78233; -106.25568 LA
Pie Town New Mexico 34°18′04″N 108°07′09″W / 34.30107°N 108.11912°W / 34.30107; -108.11912 PT
Kitt Peak Arizona 31°57′23″N 111°36′44″W / 31.956253°N 111.612361°W / 31.956253; -111.612361 KP
Owens Valley California 37°13′54″N 118°16′38″W / 37.23176°N 118.27714°W / 37.23176; -118.27714 OV
Brewster Washington 48°07′52″N 119°41′00″W / 48.13117°N 119.68325°W / 48.13117; -119.68325 BR
Mauna Kea Hawaii 19°48′06″N 155°27′21″W / 19.80159°N 155.45581°W / 19.80159; -155.45581 MK

Four other sites are brought online for as much as 100 hours per four-month trimester. In this configuration, the entire array is known as the High-Sensitivity Array.[3] These sites, with coordinates, are as follows:

Very Long Baseline Array is located in World
St. Croix
Mauna Kea
Arecibo
Effelsberg
VLBA locations around the world
Toponymy State Geographic coordinate system
Arecibo Puerto Rico 18°20′36.60″N 66°45′11.10″W / 18.3435°N 66.753083°W / 18.3435; -66.753083 AR
Green Bank West Virginia 38°25′59.24″N 79°50′23.41″W / 38.4331222°N 79.8398361°W / 38.4331222; -79.8398361 GB
Very Large Array New Mexico 34°04′43.75″N 107°37′05.91″W / 34.0788194°N 107.6183083°W / 34.0788194; -107.6183083 Y27
Effelsberg Germany 50°31′30″N 6°53′00.3″E / 50.525°N 6.883417°E / 50.525; 6.883417 EB

Contents

[edit] Baseline distance and angular resolution

Distance between each VLBA baseline (km):[4]

SC HN NL FD LA PT KP OV BR MK EB AR GB Y27
SC ... 2853 3645 4143 4458 4579 4839 5460 5767 8611 6822 238 2708 4532
HN 2853 ... 1611 3105 3006 3226 3623 3885 3657 7502 5602 2748 829 3198
NL 3645 1611 ... 1654 1432 1663 2075 2328 2300 6156 6734 3461 1064 1640
FD 4143 3105 1654 ... 608 564 744 1508 2345 5134 8084 3922 2354 515
LA 4458 3006 1432 608 ... 236 652 1088 1757 4970 7831 4246 2344 226
PT 4579 3226 1663 564 236 ... 417 973 1806 4795 8014 4365 2551 52
KP 4839 3623 2075 744 652 417 ... 845 1913 4466 8321 4623 2939 441
OV 5460 3885 2328 1508 1088 973 845 ... 1214 4015 8203 5255 3323 1025
BR 5767 3657 2300 2345 1757 1806 1913 1214 ... 4398 7441 5585 3326 1849
MK 8611 7502 6156 5134 4970 4795 4466 4015 4398 ... 10328 8434 7028 4835
EB 6822 5602 6734 8084 7831 8014 8321 8203 7441 10328 ... 6911 6335 8008
AR 238 2748 3461 3922 4246 4365 4623 5255 5585 8434 6911 ... 2545 4317
GB 2708 829 1064 2354 2344 2551 2939 3323 3326 7028 6335 2545 ... 2516
Y27 4532 3198 1640 515 226 52 441 1025 1849 4835 8008 4317 2516 ...

Minimum angular resolution:

Wavelength (cm) 90 50 21 18 13 6 4 2 1 0.7
θHPBW (mas) 22 12 5.0 4.3 3.2 1.4 0.85 0.47 0.32 0.17

[edit] See also

[edit] References

  1. ^ Saha, Swapan Kumar (2010), Aperture Synthesis: Methods and Applications to Optical Astronomy, Astronomy and Astrophysics Library, Springer, p. 81, ISBN 144195709X, http://books.google.com/books?id=BIHe2Mmv08cC&pg=PA81 
  2. ^ Lèna, Pierre et al. (2012), Observational Astrophysics, Astronomy and Astrophysics Library (3rd ed.), Springer, ISBN 3642218148, http://books.google.com/books?id=jvrnX7iZ5mEC&pg=PA282 
  3. ^ "NRAO Antenna Sites". http://www.vlba.nrao.edu/astro/obstatus/current/node5.html. 
  4. ^ "NRAO Website". http://www.vlba.nrao.edu/astro/obstatus/current/node30.html. 

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