Combined Array for Research in Millimeter-wave Astronomy

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The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is an astronomical instrument to be composed of 23 radio telescopes. The signals detected by these telescopes are combined to form an interferometer. According to the CARMA observatory catalog, the median height of all telescope pads are at an elevation of 2196.223 m (7205.807 ft). The observatory is 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.

Until the Atacama Large Millimeter Array is constructed in Chile, this instrument will be the most powerful millimeter wave interferometer in the world. This array is unique for being a heterogeneous collection of radio telescopes of varying sizes and design. There are three types of telescopes.

9 Telescopes each 6.1 meters (20 feet) in diameter. These were once 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.
8 Telescopes each 3.5 meters (11.5 feet) in diameter. These were newly built and are also known as the Sunyaev-Zel'dovic Array (SZA), a project lead by John Carlstrom at the University of Chicago. The SZA is currently observing the sky on the valley floor of the Owens Valley Radio Observatory and will be moved up to Cedar Flat sometime in 2007. The array presently observes radio waves with a wavelength of 1 cm (about 22 GHz).
6 Telescopes each 10.4 meters (34 feet) in diameter. These were once part of the Millimeter Array at the OVRO site. They were moved to Cedar Flat in the spring of 2005.

As of November 2006, the 9 telecopes from the BIMA array and the 6 telescopes from the OVRO array are working together to gather scientific data. The process of instrument commissioning is on-going.

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.