The Very Large Array Expansion Project

TheVeryLargeArrayExpansionPro jectMichaelP.Rup enaaNational Radio AstronomyObservatory,1003 Lop ezville Road, So corro, NM,USAABSTRACTThe National Radio Astronomy Observatory (NRAO) is undertaking a ma jor expansion of the Very Large Array(VLA), the most p owerful and exible radio instrumentinthe world.This VLA Expansion Pro ject combines theexisting infrastructure with state-of-the-art electronics and instrumentation to improve the scienti c capabilitiesof the arrayby a factor 10 or more in all key observational parameters.Some of the most imp ortantadvancesinclude:(1)replacingtheexistingwaveguide withoptical b er,allowingtotalbandwidthsofupto16 GHz,rather than the current 200 MHz; (2) installing wideband receiver systems, for continuous coverage of the entirecentimeter radio sp ectrum from1 to 50 GHz; (3) building a new correlator, able to provide as manyas262,144frequency channels with exible, variable resolutions b etween 4 MHz and 1 Hz; (4) adding8 new stations atdistances up to 300 km from the current VLA, allowing spatial resolution as high as a fewmilliarcseconds onbothsynchrotron andthermalsources.Thedesign anddevelopmente ort forthe rstphaseofthispro jecthasalreadyb egun,andwearecurrentlydevelopingaprop osalforthenewantennasneededhigh-resolution New Mexico Array.There are three ma jor partners in the EVLA: NRAO; the Herzb erg Institute ofAstrophysics (HIA),fundedbytheNationalResearch Council(NRC)ofCanada;andMexicanCouncil for Science and Technology (CONACyT). Weplan to nish theentire pro ject withina decade.TheEVLA will inaugurate a new era in radio astronomy, allowing extinction-free imaging of star-forming galaxiesout toz>5, measurements of the three-dimensional structure of magnetic elds in ob jects ranging from the Sunto nearby galaxies, and parallaxes and prop er motion measurements of pulsars spread throughout the Galaxy.The EVLA is intended not to p erform a single, particular exp eriment,but to provide an essential to ol acrossthe entire range of mo dern astrophysics.Keywords:New telescop es, ground-based astronomy, radio astronom,interferometry, ap erture synthesis1. INTRODUCTIONThe Very Large Array (VLA) is the most p owerful, exible, and widely-used radio telescop e in the world.Sinceits dedication in 1980, it has b een used by more than 2200 researchers for more than 10,000 di erent observingpro jects.Thesepro jectsspanthefullrangeofmo dernastronomy,fromimagingcollidingstellarwinds,toexploringenergyinputfromactivegalacticnucleiintothetergalacticmedium,mappingoutmagnetic eldstructuresinnearbygalaxies.ItisatributetotheoriginaldesignofVLAthatthistweny-year-old instrument can still make imp ortant scienti c contributions;at thesametime itis clear thatthe world'spremier radio telescop e is enormously limitedby employing decades-old technology, esp ecially in the areas ofsignal transmission and data pro cessing.The goal of the VLA Expansion Pro ject is to remove these limitationsbyincorp oratingnewlyavailabletechnologiesintothesoundbasicdesignandexistinginfrastructureofVLA, and by expanding the array spatially by the addition of new antennas at lo cations up to 300 km from thecurrent VLA. The result will e ectively b ean entirely new instrument { the Expanded VLA (EVLA) { withorder-of-magnitude improvements in all key observational characteristics, at a fraction of the cost of the originalobservatory.FollowingastrongendorsementbytheMcKee-TylorDecadalSurvey,1NationalScienceFoundation(NSF)approvedfundingforthe rstpartofpro jecton15Noember2001,withadditionalsupp ort coming from Canada's National Research Council (NRC), and Mexico's Consejo Nacional de Ciencia yTecnologa (CONACyT). The National Radio Astronomy Observatory (NRAO)is currently preparing a planFurther author information:E-mail:mrup en@nrao.edu, Telephone:1 505 835-7248The National Radio Astronomy Observatory is a facility of the National Science Foundation op erated under co op-erative agreementby Asso ciated Universities, Inc.