Combined Array for Research in Millimeter-wave Astronomy


The Combined Array for Research in Millimeter-wave Astronomy (CARMA) was an astronomical instrument comprising 23 radio telescopes, dedicated in 2006.[1] These telescopes formed an astronomical interferometer where all the signals are combined in a purpose-built computer (a correlator) to produce high-resolution astronomical images.[2] The telescopes ceased operation in April 2015 and were relocated to the Owens Valley Radio Observatory for storage.

Combined Array for Research in Millimeter-wave Astronomy
Alternative namesCARMA Edit this on Wikidata
Part ofOwens Valley Radio Observatory Edit this on Wikidata
Location(s)California, Pacific States Region
Coordinates37°16′49″N 118°08′31″W / 37.2804°N 118.142°W / 37.2804; -118.142 Edit this at Wikidata
OrganizationCalifornia Institute of Technology Edit this on Wikidata
Altitude2,196 m (7,205 ft) Edit this at Wikidata
First light2005 Edit this on Wikidata
Telescope styleradio interferometer Edit this on Wikidata Edit this at Wikidata
Combined Array for Research in Millimeter-wave Astronomy is located in the United States
Combined Array for Research in Millimeter-wave Astronomy
Location of Combined Array for Research in Millimeter-wave Astronomy
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The Atacama Large Millimeter Array in Chile has succeeded CARMA as the most powerful millimeter wave interferometer in the world.[citation needed]

Location edit

According to the CARMA observatory catalog, the median height of all telescope pads was at an elevation of 2,196.223 meters (7,205.456 ft). The observatory was located in the Inyo Mountains to the east of the Owens Valley Radio Observatory, at a site called Cedar Flat (after relocating the Cedar Flat Group Camps to the west of Hwy-168), accessed through Westgard Pass. The high elevation site was chosen to minimize millimeter wave absorption and phase decoherence by atmospheric water vapor.

Features edit

This array was unique for being a heterogeneous collection of radio telescopes of varying sizes and design. There were three types of telescopes, all Cassegrain reflector antennas with parabolic primary mirrors and hyperbolic secondary mirrors:

  • Six telescopes each 10.4 meters (34 ft) in diameter. These were part of the Millimeter Array at the OVRO site operated by Caltech. They were moved to Cedar Flat in the Spring of 2005.
  • Nine telescopes each 6.1 m (20 ft) in diameter. These were formerly located at the Hat Creek Radio Observatory and operated by the Berkeley-Illinois-Maryland-Association (BIMA) consortium. These were moved from HCRO in the spring of 2005 to Cedar Flat.
  • Eight telescopes each 3.5 m (11 ft) in diameter. These were built as an instrument for cosmology and are also known as the Sunyaev-Zel'dovich Array (SZA), a project led by John Carlstrom at the University of Chicago. The SZA spent three years on the valley floor at the Owens Valley Radio Observatory observing the cosmic microwave background (CMB) and galaxy clusters. In the summer of 2008 it was moved up to Cedar Flat.

Deployment edit

CARMA in 2012

As of November 2006, the six telescopes from the OVRO array and the nine telescopes from the BIMA array were working together to gather scientific data. Pioneering work on compensating for the image distortion resulting from turbulent water vapor distributions in the troposphere started in the fall of 2008.

The most extended configurations of the array, up to 2 kilometers (1.2 mi), were required for viewing the finest details in astronomical images.[citation needed] Over these distances the variation in the time of arrival of signals at the different telescopes as they pass through different amounts of water vapor severely limits the quality of images.[3]

By siting an SZA antenna near each of the CARMA antennas and observing a compact astronomical radio source near the source under study, the properties of the atmosphere could be measured on time scales as short as a couple of seconds. This information could be used in the data reduction process to remove a significant fraction of the degradation caused by the atmospheric scintillation.[4]

Observations using the SZA (operating at 30 GHz) to make the atmospheric measurements started in November 2008. The SZA has also participated directly in the science operations of CARMA during experiments where all three types of telescopes were attached to the same correlator.

Observations were primarily in the 3 mm range (80–115 GHz) and the 1 mm range (210–270 GHz). These frequencies are useful for detecting many molecular gases, including the second most abundant molecule in the universe, carbon monoxide (CO).

Observing CO is an indirect indicator of the presence of molecular hydrogen gas (the most abundant molecule in the universe) which is difficult to detect directly. Cold dust is also detectable in this wavelength range and can be used to study planet-forming disks around stars, for example. In 2009, the OVRO 10.4 m antennas were instrumented with 27–35 GHz receivers and made observations in the centimeter band in concert with the SZA antennas.[citation needed]

VLBI edit

CARMA telescopes in 2012

CARMA was an array element in the early proof of concept observations by the Event Horizon Telescope project, and in 2007 participated in observations which showed that event-horizon-scale structures could be seen in the Milky Way's supermassive black hole, Sgr A*.[5]

Universities involved edit

CARMA was a consortium composed of three primary groups.

California Institute of Technology, Berkeley-Illinois-Maryland Association (BIMA), University of Chicago

See also edit

References edit

  1. ^ "CARMA Radio Telescope Array in the Inyo Mountains Dedicated May 5". California Institute of Technology. 2006-05-04. Retrieved 2021-12-01.
  2. ^ Douglas Bock and the CARMA Team, Combined Array for Research in Millimeter-wave Astronomy, From Planets to Dark Energy: the Modern Radio Universe, October 1-5 2007, The University of Manchester, UK
  3. ^ The temporal power spectrum of atmospheric fluctuations due to water vapor (
  4. ^ "Beating atmospheric scintillation at millimeter and submillimeter wavelengths". Retrieved 2021-12-01.
  5. ^ Doeleman, Shepard S.; Weintroub, Jonathan; Rogers, Alan E.E.; Plambeck, Richard; Tilanus, Remo P.J.; Friberg, Per; Ziurys, Lucy M.; Moran, James M.; Corey, Brian; Young, Ken H.; Smythe, Daniel L.; Titus, Michael; Marrone, Daniel P.; Cappallo, Roger J.; Bock, Douglas C.J.; Bower, Geoffrey C.; Chamberlin, Richard; Davis, Gary R.; Krichbaum, Thomas P.; Lamb, James; Maness, Holly; Niell, Authur E.; Roy, Alan; Strittmatter, Peter; Werthimer, Daniel; Whitney, Alan R.; Woody, David (4 September 2008). "Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre". Nature. 455 (7209): 78–80. arXiv:0809.2442. doi:10.1038/nature07245. PMID 18769434. S2CID 4424735. Retrieved 21 November 2020.
  6. ^
  7. ^

External links edit

  • CARMA Website
  • OVRO Website
  • BIMA Website
  • Sunyaev-Zeldovich observations at BIMA and OVRO
  • CARMA: Specifications & Status, 2002