HCRO began in the late 1950s and has been a pioneer in radio astronomy for nearly half a century. Scientists detected polyatomic molecules in space for the first time here. HCRO has also been the site of one of the first millimeter-wave interferometers. An interferometer is an array of dishes connected together to provide information similar to a larger single-dish. Much of what scientists know about star formation today came from observations made by our millimeter-wave interferometer.
One of the primary instruments at HCRO was an 85-foot diameter antenna that was installed in 1962. With the 85 ft dish, astronomers discovered the first interstellar maser, the radio analogue of a laser. Other firsts at Hat Creek include the discovery of polyatomic molecules in space, like water and ammonia.
In the 1970’s Berkeley astronomers developed a centimeter wavelength radio interferometer at HCRO. The interferometer was used to accurately measure positions of water vapor masers in star-forming regions, to image giant radio galaxies like M87 and Cygnus A, and to study supernova remnants like the Crab Nebula.
Starting with two dishes operating at wavelengths near 1 centimeter, the interferometer evolved into an array of 10 dishes operating at wavelengths of 1 to 3 millimeters.
The 10-element array was called BIMA, named after the consortium of universities that operated and helped fund the instrument (Berkeley, Illinois, and Maryland Association).
The shift to shorter wavelengths produced new results not possible before. The array was capable of studying the details of proto-stellar disks (sites of planet and star formation) and of imaging molecular clouds and entire galaxies in the radio emissions from CO (carbon monoxide) and other molecules. These included large organic molecules like formic acid, acetic acid, and glycolaldehyde found in the Galactic Center and other star-forming regions. Detecting these molecules in space suggests that life on earth may be intimately related to the organic chemistry of interstellar space. Perhaps these large molecules were delivered to the primordial earth, providing a jump-start to life on our planet.
Even though the BIMA Array produced outstanding scientific discoveries for more than a decade, water vapor within the atmosphere above Hat Creek limited the sensitivity at the shortest wavelengths. For this reason the BIMA Array has been moved to a higher elevation site in a drier location. It has joined six telescopes from the Owens Valley Radio Observatory operated by Caltech to make a new array called CARMA (Combined Array for Research in Millimeter-wave Astronomy). The CARMA array is located at a new site in the Inyo Mountains, at an elevation of 7,200 feet, near Bishop, CA.
Right now HCRO is installing the ATA. Each ATA antenna is 20 feet in diameter and uses an offset Gregorian focus. That is, the receiver is placed off of the axis of symmetry of the dish in order to provide a cleaner signal. The telescopes are actually looking at a much higher angle than you might think! (Estimate from the bottom of the large dish to the top of the small dish). The individual dishes work together to provide the collecting power of all dishes combined and the resolving power (ability to see fine detail) of a much larger dish.
The decision to build the ATA at HCRO was based largely on the site’s low-interference environment. Situated in Hat Creek Valley surrounded by volcanic mountains, HCRO is well isolated from man-made radio interference. Eliminating terrestrial interference is critical in the search for extraterrestrial intelligence.
The completed ATA will be have an incredible field of view and angular resolution as well as very fast imaging speed. One of the first targets for convetional radio astronomy here will be to map all the hydrogen (position, mass, velocity) in our galaxy and then the intergalactic neiborhood. Hydrogen is 90% of all matter so this data helps astronomers better understand the structure of our galaxy, including the evidence for the elusive dark matter out there. Amazingly SETI will be able to conduct their search at the same time as this is happening! Another project will be to monitor the sky for time varying, or transient, radio sources. Many of these originate in processes involving super-massive black holes in the centers of galaxies, distant supernova explosions, and gamma-ray bursts. Discovering where and how often transient sources occur in the universe will improve our understanding of these exotic objects.
Original text by Sanj Brar. Edited, updated, reformatted, and some additions by Brian Kearney. Visual and layout redesign by Colby Gutierrez-Kraybill