Combined Array for Research in Millimeter-wave Astronomy
The Combined Array for Research in Millimeter-wave Astronomy was an astronomical instrument comprising 23 radio telescopes. These telescopes formed an astronomical interferometer where all the signals are combined in a purpose-built computer to produce high-resolution astronomical images. The telescopes ceased operation in April 2015 and were relocated to the Owens Valley Radio Observatory for storage. The Atacama Large Millimeter Array in Chile has succeeded CARMA as the most powerful millimeter wave interferometer in the world.
Location
According to the CARMA observatory catalog, the median height of all telescope pads was at an elevation of. The observatory was located in the Inyo Mountains 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.
Features
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 in diameter. These were part of the Millimeter Array at the OVRO site operated byCaltech. They were moved to Cedar Flat in the Spring of 2005.
Nine telescopes each in diameter. These were formerly located at the Hat Creek Radio Observatory and operated by the consortium. These were moved from HCRO in the spring of 2005 to Cedar Flat.
, 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, were required for viewing the finest details in astronomical images. 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 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. Observations using the SZA 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 and the 1 mm range. These frequencies are useful for detecting many molecular gases, including the second most abundant molecule in the universe, carbon monoxide. Observing CO is an indirect indicator of the presence of molecular hydrogen gas 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.
