PRIMA Astrometric FItting Software (AFIS)

Transcription

1 PRIMA Astrometric FItting Software (AFIS) Users Requirements Doc. Nr: JRA4-SPE Issue: 1.0 Date: July 15 th, 2006 Prepared Damien Ségransan July 15 th, 2006 Approved Gérard Zins Released Signature Signature Signature

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3 PRIMA Astrometric FItting Software (AFIS)Users Requirements Issue 1.0 JRA4-SPE Change Record Issue Date Section/Parag. affected Reason/Initiation/Documents/Remarks July-2006 all First concept

4 Contents iv

5 List of Figures v

6 List of Tables vi

7 PRIMA Astrometric FItting Software (AFIS)Users Requirements Issue 1.0 JRA4-SPE Scope The Astrometric FItting Software (AFIS) will be made available as a contribution of Geneva Observatory to the JRA4. AFIS is a software that allows to analyse data taken with VLTI using the astrometric mode of PRIMA. AFIS allows to fit for relative parallaxes and proper motion as well as for orbital elements of binary stars or planets.

8 Introduction The Astrometric FItting software (AFIS) is the last stage of the observations. Its goal is to extract the astrophysical information out of reduced astrometric data and radial velocity data. In the specific case of extrasolar planet search and characterisation, AFIS will allow to derive the orbital parameters of the planet s parent star as well as the mass of the planet. Scientific and Technical Goals The primary objective and main science driver for developing the high-precision narrow-angle astrometric facility at the VLTI is the detection and characterization of extra-solar planets. However, to play a significant role, an astrometric accuracy of order 10 µarcsec is necessary, which is close to the fundamental limit set by atmospheric turbulence (on a m baseline at a high-altitude site with excellent seeing, arcsec separation between target and reference star, and hr integration time). The ultimate technical goal of the PRIMA-DDL/AOS project is to develop and integrate into the VLTI/PRIMA system hard- and software that allows to routinely and over the duration of many years measure the angular separation between two stars which are separated by arcsec with an absolute 1σ (rms) accuracy of 10 µarcsec. When completed in 2008, we will use the upgraded PRIMA system to carry out a large observing program to detect and characterize extra-solar planets by measuring the 2-dimensional reflex motion of their host stars in the plane of the sky. PRIMA Astrometry Operation Concept The Phase Referenced Imaging and Micro-arcsecond Astrometry (PRIMA) facility is a system designed to enable simultaneous interferometric observations of two objects each with size of at most 2 arcsec that are separated by up to 1 arcmin, without requiring a large continuous field of view [?]. The maximum separation between the two objects is given by the isoplanatic angle, which depends on the observing wavelength and the atmospheric conditions. In addition, it is constrained by field of view of the M10 star separator mirror. In most cases, only one of the two objects, usually the brighter one, is of scientific interest, while the scientific observable is the angular separation vector between the two stars. The actual scientific target, i.e., the position (or change of position) of the science star has to be deduced via assumptions and models from this observable. 2

9 Chapter 1 Functional Requirements 1.1 Functionality and user interfaces of the AFIS AFIS: Basic functions AFIS is a standalone software that allow to retrieve relative parallaxes, relative proper motions as well as the orbital parameters of binary stars or of stars hosting a planet. AFIS will use the classical levenberg marquardt minimisation algorithm of a Chi2 function. AFIS will also compute error bars resulting from the diagonal terms of the covariance matrix of the fit and will compute correlation between the fitted parameters. Basic functions 1. Parallactic motion computation 2. Astrometric orbital motion computation 3. Radial Velocity orbital motion computation (if rv provided) 4. Minimisation function 5. Correlation function 6. Several GUI that allow to pass parameters to the previous functions AFIS: Inputs All data of a given project (or several projects): 1. Date 2. Differential phase measurements and their error (interface with DAF) 3. Radial velocities and their errors 4. Guess for initial fit parameters 3

10 4 PRIMA Astrometric FItting Software (AFIS)Users Requirements Issue 1.0 JRA4-SPE AFIS: Outputs The main output of the IDAF are relative parallaxes between the target and its reference stars as well as the orbital parameters provided that the target is a binary star or that it is orbited by a planet. 1. Chi2 2. Relative Parallax and proper motions and their errors 3. Orbital parameters, planet mass and errors 4. Correlation between the fitted parameters 4. Residuals, Chi2 probability AFIS: User interfaces AFIS will be a java applet that can be loaded by most of the web browser. It will also be possible to launch it locally using any java applet viewer compatible with JDK AFIS will have a GUI very similar to APES (Astrometric observations PrEparation Software, segransa/apes/protoapes/welcome alpha.html) that will allow to load all input parameter. The configuration of the fitting algorithm will also be accessible through the GUI. AFIS will also be able to plot orbits with the astrometric measurements (similar to APES) as well as residuals.

11 Chapter 2 Operational Requirements 2.1 Operation of the AFIS AFIS will be user friendly enough that it could be used by any astronomer who should provide correctly reduced data. Of course, the user should be aware of the basic pitfall of fitting algorithm. AFIS could be runned online or offline depending on the user needs. 2.2 Software development, platforms, and documentation Software evolution over time The design of the software should allow evolution over time since it is object oriented Software distribution and installation The software packages should be self-contained and distribution and easy installation should be possible after a detailed development phase (e.g., via CVS) Platforms and environments The software should run on any machine with java runtime environement 1.5 or later. It could be runned through a web server or locally using any java applet viewer Documentation The software and all its modules must be fully documented. The documentation must be sufficient such that others can install, upgrade, and operate the software independent of the developers. Documentation in electronic form is sufficient. The goal is to have documentation on a WWW-server on a central location, for easy upgrades. ooo 5