The Allen Telescope Array: Science Operations
Intellectual Merit: The Allen Telescope Array (ATA) is a pioneering centimeter-wavelength radio telescope that will produce science that cannot be done with any other instrument. The ATA is the first radio telescope designed for commensal observing; it will simultaneously undertake the most comprehensive and sensitive SETI surveys ever done as well as the deepest and largest area continuum and spectroscopic surveys. The science of the ATA is enabled by a wide range of innovative technical developments. The astronomy decadal panel, Astronomy and Astrophysics in the New Millenium, endorsed SETI and recognized the ATA (then, the 1 Hectare Telescope) as an important stepping-stone to the Square Kilometer Array (SKA), its highest ranked "moderate project" in radio astronomy. Located in Hat Creek, CA, formerly the site of the BIMA Array, the array currently consists of 42 6.1-m diameter antennas with continuous frequency response from 0.5 to 11.2 GHz. Science operations commenced in mid-2007. Highlights include large-scale continuum mosaics, a high-quality single-pointing image of the entire Andromeda galaxy in HI, and a 500-hour search for fast radio transients. A call for external proposals netted 24 proposals requesting 1200 hours of observing time in a wide range of fields. The wide field of view of the ATA enables a survey capability that is comparable to large single dish telescopes and within a factor of a few of the current Very Large Array (VLA). The compact configuration of the ATA and the high density of antennas provides unprecedented snapshot imaging quality as well as a resolution that is intermediate between the most compact VLA configuration and that of the largest single dishes. The frequency range of the ATA permits sensitive observations at frequencies rarely studied. Finally, the use of two separate correlators at two independently-tunable frequencies and the simultaneous ability to synthesize multiple independently-located phased array beams at four independently-tunable frequencies gives the ATA the capability to conduct a wide range of science at once. Even with 42 elements, the ATA is a powerful radio survey telescope. Science goals include a 5 GHz continuum survey to match the 7.4-GHzN RAO VLA Sky Survey and the Sloan Digital Sky Survey within the first year of operation, and a survey of extragalactic hydrogen in the nearby universe to investigate galaxy evolution and intergalactic gas accretion. Transient and variable source surveys, pulsar science, spectroscopy of new molecular species in the galaxy, large-scale mapping of galactic magnetic filaments, and wide-field imaging of comets and other solar system objects are among the other key science objectives of the ATA. SETI surveys will target the inner Galactic plane for very luminous transmitters and hundreds of nearby stars, in some cases with sensitivities to terrestrial-level signals.
Broader Impact: The Large-N, small-diameter (LNSD) concept that underlies the ATA design is the basis for the USA and international designs for the SKA. Much of the technical development related to the ATA is important for the SKA and a range of new radio facilities employing the LNSD concept. Operation of the ATA will demonstrate the value of these in the best possible way - through science goals that cannot be otherwise achieved. The ATA has been and will continue to be the training ground for the next generation of centimeter-wave astronomers and instrumentalists. Eighteen graduate and undergraduate students have already been involved with the hardware and firmware design of the ATA. Additional students and postdocs have been involved in commissioning, calibrating and observing. SETI science has a public appeal and a potential reward that go far beyond that of other fields of astronomy. The ATA and its SETI program will continue to draw worldwide attention to radio astronomy. The appeal of SETI has already drawn the private investment into the ATA that has enabled its development and construction, creating a new model for public and private collaboration in radio astronomy.