FULL TITLE ASP Conference Series Vol VOLUME YEAR OF PUBLICATION NAMES OF EDITORS Status of the Atacama Large Millimeter Array

The Atacama Large Millimeter Array ALMA is a large inter national telescope project which will be built over the next decade in northern Chile on a site at km elevation The site provides excellent atmospheric trans mission in the millimeter and sub millimeter wavelength ranges The project consists of two parts the m Array composed of sixty four meter antennas that can be placed on di erent stations for baselines up to km see Table and the Atacama Compact Array or ACA that consists of twelve meter telescopes placed in compact con gurations and four meter telescopes for measuring source total power In addition to high sensitivity frequency coverage and dynamic range ALMA will record both interferometric and the complete source ux density At the shortest planned wavelength mm and longest baseline the angular resolution will be The receivers use superconducting SIS mixers to provide the lowest possible receiver noise contribution At rst light the ALMA project the highest priority receiver bands will be installed see Table each observing both polarizations with a bandwidth of GHz In the following we present the status of the ALMA project as of late Introduction and Science Requirements The ALMA project will provide an instrument uniquely capable of producing detailed images in the continuum and in spectral lines in the wavelength re gion from to mm These data will allow new insights into the formation of galaxies stars planets and the chemical precursors necessary for life itself ALMA is the appropriate successor to the present generation of millimeter wave interferometer arrays ALMA will be able to image dust enshrouded or cold material and will complement meter optical near IR telescopes such as the Very Large Telescope VLT Gemini Subaru LBT and Keck and to the Hubble Space Telescope and its successor the James Webb Space Telescope matching or exceeding the angular resolution of any of these facilities The highest level science requirements that have determined the ALMA parameters are the ability to detect spectral line emission from rotational spectral lines of the carbon monoxide molecule atomic and ionized carbon in a Wilson Beasley and Wootten galaxy with the properties of the Milky Way at a redshift of z in less than hours of measurement image the kinematics of gas in protostars and protoplanetary disks around young solar type stars out to a distance of light years This represents the distance to the nearby well known clouds in Ophiuchus Taurus or Corona Australis and provide precise images at an angular resolution better than Here precise means that the ratio of the most intense to weakest feature in the image can reach This applies to sources that transit at more than o elevation at the ALMA site For more general science goals ALMA will allow users to Image the broadband emission from dust in evolving galaxies at epochs of formation as early as z trace through measurements of molecular and atomic spec tral lines the chemical composition of star forming gas in galaxies throughout the history of the universe Measure the motions of obscured galactic nuclei and Quasi Stellar Objects on spatial scales ner than light years Image gas rich heavily obscured regions that are collapsing to form protostars proto planets and pre planetary disks Determine the crucial isotopic and chemical gradients within circumstellar shells that re ect the chronology of stellar nuc lear processing obtain sub arcsecond images of cometary nuclei hundreds of asteroids Centaur and Kuiper belt objects together with images of planets and their moons and Image active solar regions to investigate particle accelera tion on the suns surface For more complete descriptions of ALMA science see Wilson The Dusty and Molecular Universe or Wootten Science with the Atacama Large Millimeter Array General Description of the Project ALMA is a revolutionary instrument in its scienti c concept engineering design and organization as a global scienti c endeavor ALMA is an equal partner ship between Europe and North America in cooperation with the Republic of Chile and is funded in North America by the U S National Science Foundation NSF in cooperation with the National Research Council of Canada NRC and in Europe by the European Southern Observatory ESO and Spain In the bilateral project ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory NRAO which is managed by Associated Universities Inc AUI and on behalf of Europe by ESO In addition Japan has also entered the ALMA project A preliminary agreement has been signed by all partners and a nal agreement is expected to be signed in The Japanese contribution to the enhanced ALMA will be the construction of the ACA an array of twelve meter antennas plus four meter dishes that will be used to measure the total power and two additional receiver bands ALMA will be an interferometer array operating in the millimeter sub millimeter wavelength range It is the natural extension of existing millimeter interferometer arrays but on a vastly larger scale on an excellent observing site ALMA is a revolutionary instrument in its scienti c concept engineering design and organization it is a global scienti c undertaking In the following we present a description of the basic and ultimate versions of the project and indicate how the scienti c objectives have led to the technical speci cations and Status of the Atacama Large Millimeter Array operations plan More details about the ALMA project and design can be found at the website http www alma info These publications contain a complete set of references In the following we describe the baseline ALMA plan as of late Table ALMA Antenna Arrays and Con gurations Array Main Compact ACA Number of Antennas Total Collecting Area m Array Con gurations dimension of lled area Compact lled m m Largest Extent km Total No of antenna stations Antennas Diameter m m m Surface accuracy m m m m m a Transportable by specially constructed vehicle with rubber tires Table First Light Front Ends on all Antennas Band mm GHz SIS Band mm GHz SIS Band mm GHz SIS Band mm GHz SIS Band mm GHz SIS Band mm GHz SIS Water Vapor Radiometer mm GHz Schottky a Baseline ALMA plan all are planned to have dual polarization with noise performance limited by atmosphere The ALMA sensitivity calculator is at http www eso org projects alma science bin sensitivity html