Combined Array for Research in Millimeter-wave Astronomy
Encyclopedia
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is an astronomical instrument comprising 23 radio telescopes. These telescopes form an astronomical interferometer
where all the signals are combined in a purpose-built computer (a correlator) to produce high-resolution astronomical images.
to the east of the Owens Valley Radio Observatory
, at a site called Cedar Flat, accessed through Westgard Pass
. The high elevation site was chosen to minimize millimeter wave absorption and phase decoherence by atmospheric water vapor.
Until the Atacama Large Millimeter Array
in Chile is in full operation, this instrument will be the most powerful millimeter wave interferometer in the world.
antennas with parabolic primary mirrors and hyperbolic secondary mirrors:
The most extended configurations of the array required for viewing the finest details in astronomical images, the telescopes are separated by up to 2 km. 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.
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 can be measured on time scales as short as a couple of seconds. This information can be used in the data reduction process to remove a significant fraction of the degradation caused by the atmospheric scintillation.
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 are 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 will be instrumented with 27-35 GHz receivers and be able to make observations in the centimeter band in concert with the SZA antennas.
California Institute of Technology, Berkeley-Illinois-Maryland Association (BIMA), University of Chicago
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....
where all the signals are combined in a purpose-built computer (a correlator) to produce high-resolution astronomical images.
Location
According to the CARMA observatory catalog, the median height of all telescope pads is at an elevation of 2196.223 m (7205.807 ft). The observatory is located in the Inyo MountainsInyo Mountains
The Inyo Mountains are a short mountain range east of the Sierra Nevada mountains in eastern California in the United States. The range separates the Owens Valley to the west with Saline Valley to the east, extending for approximately 70 mi SSE from the southern end of the White Mountains,...
to the east of the Owens Valley Radio Observatory
Owens Valley Radio Observatory
The Owens Valley Radio Observatory is a radio observatory located near Bishop, California, within the Owens Valley, California region, approximately 250 miles north of Los Angeles on the east side of the Sierra Nevada. It is owned and operated by the California Institute of Technology. For...
, at a site called Cedar Flat, accessed through Westgard Pass
Westgard Pass
Westgard Pass is a narrow gap between the White and Inyo mountain ranges in the Basin and Range Province of California. Westgard Pass lies entirely within the Inyo National Forest, in northern Inyo County, California....
. The high elevation site was chosen to minimize millimeter wave absorption and phase decoherence by atmospheric water vapor.
Until the Atacama Large Millimeter Array
Atacama Large Millimeter Array
The Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...
in Chile is in full operation, this instrument will be the most powerful millimeter wave interferometer in the world.
Features
This array is unique for being a heterogeneous collection of radio telescopes of varying sizes and design. There are three types of telescopes, all Cassegrain reflectorCassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....
antennas with parabolic primary mirrors and hyperbolic secondary mirrors:
- 6 Telescopes each 10.4 meters (34 feet) 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.
- 9 Telescopes each 6.1 meters (20 feet) in diameter. These were formerly located at the Hat Creek Radio ObservatoryHat Creek Radio ObservatoryThe Hat Creek Radio Observatory is operated by the Radio Astronomy Laboratory in the Western United States.- Location :...
and operated by the http://bima.astro.umd.eduBerkeley-Illinois-Maryland-Association (BIMABimaBima is a city on the eastern coast of the island Sumbawa in central Indonesia's province West Nusa Tenggara, and the largest city on the island. In 2010 the municipality counted some 142,443 people, separate from the adjoining Regency of Bima with 407,636 population...
)] consortium. These were moved from HCRO in the spring of 2005 to Cedar Flat. - 8 Telescopes each 3.5 meters (11.5 feet) in diameter. These were built as an instrument for cosmology and are also known as the Sunyaev-Zel'dovich ArraySunyaev-Zel'dovich ArrayThe Sunyaev–Zel'dovich Array in California is an array of eight 3.5 meter telescopes that is now operating as part of the Combined Array for Research in Millimeter-wave Astronomy . Its initial goals were to survey the Cosmic Microwave Background in order to measure its fine-scale anisotropies...
(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 (CMBCMBCMB can mean:*The IATA airport code for Bandaranaike International Airport, Colombo – Sri Lanka's only international airport*C.M.B., the debut album of American R&B and pop group Color Me Badd...
) and galaxy clusters. In the summer of 2008 it was moved up to Cedar Flat. The array presently observes radio waves with wavelengths of 1 cm (about 30 GHz) and 3 mm (about 100 GHz).
Deployment
As of November 2006, the 6 telescopes from the OVRO array and the 9 telescopes from the BIMA array are 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 required for viewing the finest details in astronomical images, the telescopes are separated by up to 2 km. 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.
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 can be measured on time scales as short as a couple of seconds. This information can be used in the data reduction process to remove a significant fraction of the degradation caused by the atmospheric scintillation.
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 are 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 will be instrumented with 27-35 GHz receivers and be able to make observations in the centimeter band in concert with the SZA antennas.
Universities Involved
CARMA is a consortium composed of three primary groups.California Institute of Technology, Berkeley-Illinois-Maryland Association (BIMA), University of Chicago
- California Institute of TechnologyCalifornia Institute of TechnologyThe California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
http://www.caltech.edu - University of California, BerkeleyUniversity of California, BerkeleyThe University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
, Radio Astronomy Laboratory http://astro.berkeley.edu/ral - University of ChicagoUniversity of ChicagoThe University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
http://www.uchicago.edu - University of Illinois at Urbana-ChampaignUniversity of Illinois at Urbana-ChampaignThe University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
, Laboratory for Astronomical Imaging http://www.astro.uiuc.edu/projects/lai/ - University of Maryland, College ParkUniversity of Maryland, College ParkThe University of Maryland, College Park is a top-ranked public research university located in the city of College Park in Prince George's County, Maryland, just outside Washington, D.C...
, Laboratory for Millimeter-wave Astronomy http://www.astro.umd.edu/rareas/lma/
See also
- Owens Valley Radio ObservatoryOwens Valley Radio ObservatoryThe Owens Valley Radio Observatory is a radio observatory located near Bishop, California, within the Owens Valley, California region, approximately 250 miles north of Los Angeles on the east side of the Sierra Nevada. It is owned and operated by the California Institute of Technology. For...
- Atacama Large Millimeter ArrayAtacama Large Millimeter ArrayThe Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...
- Sunyaev-Zel'dovich effectSunyaev-Zel'dovich effectThe Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...
- Radio AstronomyRadio astronomyRadio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
- InterferometryInterferometryInterferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...