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	PRIMA: The VLTI Dual Feed Facility
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I. Introduction A. The goals of PRIMA B. Interferometry Tutorial C. Atmospheric and physical Constraints   II. Description A. The STS B. The PRIMET C. The FSU D. The DDL E. PRIMA Software III. Applications   IV. The Team   V. The Partners   VI. References, links					News of PRIMA , VLTI Plan of the site Executive summary
		Phase-Referenced Imaging and Micro-arcsecond Astrometry

Latest News of PRIMA June 31/07/03: Update and extension of the PRIMA website. Beginning of June/03: Kick off for the Star Separator contract. The VLTI Unit Telescopes under a chilean sunset

Last Breaking News of the VLTI ESO Press Release 17/03 (19 June 2003): A First Look at the Doughnut Around a Giant Black Hole - First detection by infrared interferometry of an extragalactic object. ESO Press Release 14/03 (11 June 2003): Flattest Star Ever Seen - VLT Interferometer Measurements of Achernar Challenge Stellar Theory. With PR Photos 15a-c/03. ESO Press Release 11/03 (13 May 2003): Sharper and Deeper Views with MACAO-VLTI - First Light" with Powerful Adaptive Optics System for the VLT Interferometer. With PR Photos 12a-j/03. ESO Press Release 25/02: New Vistas Open with MIDI at the VLT Interferometer: "First Fringes" in Mid-Infrared Spectral Region with Two Giant Telescopes (18/December/2002).

Plan of the Site

Welcome to the PRIMA Website. The plan of the site is described bye the menu at the top on the left on each page and summarized just below. We hope that you will satisfy your curiosity by surfing on the different pages of this site. Don't hesitate to send us an email for any question. Good Surfing!

Warning! The Netscape and Mozilla navigators don't recognize the greek letters, that could disturb the good reading of some pages.

Executive summary

Introduction

The Phase Referenced Imaging and Micro-arcsecond Astrometry (PRIMA) project is currently being developed by the European Southern Observatory (ESO) The objective of PRIMA is to enable simultaneous interferometric observations of two objects - each with a maximum size of 2 arcsec - that are separated by up to 1 arcmin, without requiring a large continuous field of view.

PRIMA enhances the VLTI in three key areas:

1. Sensitivity, the limiting magnitude is shifted from K= 10-13 (respectively for the ATs and the UTs ) to K=15-20,

2. Imaging of faint objects with high angular resolution (<10 milli arcsec), and

3. High precision astrometry (<10 micro arcsec) to allow planet detection

The principle of operation relies on finding within the isoplanatic angle (~1 arcmin) of the science target a sufficiently bright star that can be used as a reference star for the measurement and the stabilisation of the fringe motion induced by atmospheric turbulence. This operation mode brings faint objects within reach. Controlling additionally all optical path lengths of the reference star and of the science star inside the interferometer with a laser metrology system introduces the capability of imaging faint objects and of determining the precise angular separation between the two stars.

PRIMA and its Sub-systems

PRIMA can be subdivided into four sub-systems that are positioned in different location of the VLTI:

A Star Separator (per telescope): An optical system for the UT's and AT's located in the Coude Foci that feeds two arbitrary objects from the Coudé field of view into the delay lines of the VLTI.

A Laser Metrology System: To monitor with high accuracy (5 nm rms) the internal OPD between object and reference star. The laser beam is fed into the VLTI optics in the beam combination laboratory and travels along the same path as the star light up to the secondary mirror where a retro reflector sends the light back to the beam combination laboratory.

Differential Delay Lines: The difference of the white light fringe position of the object and of the reference star can be expressed as a differential OPD that has to be added with the differential delay line. The differential delay lines will be installed in the beam combination laboratory.

A Fringe Sensor Unit: An infrared camera measuring the position of the white light fringe providing the error signal for the fringe tracking system (FSU B). The fringe sensor unit is located in the beam combination laboratory. An identical device (FSU A) will play the role of Astrometry Detector A for astrometric measurements allowing the observation of the fringe patterns of secondary star on the same detector.

The PRIMA facility contains a number of technological challenges, in particular in the area of laser metrology, and requires careful analysis of the possible technical solutions. A feasibility study for the first four sub-systems (excluding the astrometry detector) has been performed to identify technical solutions and to obtain a financial estimate for the manufacturing of the sub-systems.

It should be emphasized that observations with PRIMA can start as soon as the first sub-systems are ready. With the star separator and the fringe sensor unit a reference star can be used for fringe tracking whilst integrating with VLTI instruments (MIDI, AMBER) on the fainter science object as described above. Although phase information is not available in this case scientific programmes can be performed like measuring angular diameters or validating limb darkening models of faint (K=15-20) stars. Phase information required for imaging and astrometry becomes available if the laser metrology system is installed.

Two scientific instruments will make use of the stabilised and calibrated fringe measurements for phase referenced imaging: AMBER in the near infrared (1-2.2 microns) and MIDI in the mid infrared (10-20 microns).

I. Introduction A. The goals of PRIMA B. Interferometry Tutorial C. Atmospheric and physical Constraints   II. Description A. The STS B. The PRIMET C. The FSU D. The DDL E. PRIMA Software III. Applications   IV. The Team   V. The Partners   VI. References, links

Science with PRIMA The scientific potential of PRIMA is huge and covers stellar as well as extra-galactic topics: Star formation - determining the duplicity of massive stars in young open clusters, stars in late stages of evolution - observing the immediate vicinity and the surfaces of far evolved stars yielding information on stellar atmospheres and mass loss, stellar dynamics - measurements of differential proper motions between stars in globular clusters, Quasars and active galactic nuclei - investigating the nature of the relative contributions of a circumnuclear starburst and a compact nuclear source, Extra galactic astrometry - determining the so-called AGN Dance-centroid due to SN explosion, and last but not least, The galactic center - the galactic center will be a target for imaging as well as for astrometry. The main goals are the search for a counterpart of the radio source Sgr A*, the very center of our galaxy, which is difficult at lower spatial resolutions because of severe crowding, and the measurement of radial velocities and proper motions of individual stars in the Galactic Center cluster providing strong arguments for the presence of a massive black hole in the center of our Galaxy, Substellar companions and planet detection. The situation in the area of the search of substellar companions and planet detection has changed drastically over the last few years with the discovery, mostly with radial-velocity techniques, of more than a dozen substellar objects.The sensitivity of these techniques is limited for separations lower than 2AU and they only provide a measurement of the minimum mass of the companion, leaving uncertainties on the real nature of the detected companions. Determining the very low mass companions is a key issue for understanding if there is a critical mass separating giant planets from brown dwarfs. The astrometric accuracy of PRIMA allows us to easily detect Jupiter and Saturn-like planets.

Send comments to <fdeplan@eso.org> Last update: Jul.31 2003