The Gaia astrophysical parameters inference system (Apsis)

Pre-launch description

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: calj@mpia.de
² Fac. Informática, Universidade da Coruña, Campus de Elviña, 15071 A Coruña, Spain
³ Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, PO Box 20048, 11810 Athens, Greece
⁴ Dpt. Statistics and Operations Research, University of Cádiz, Campus Universitario Río San Pedro s/n., 11510 Puerto Real, Cádiz, Spain
⁵ Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice, France
⁶ Dpt. de Inteligencia Artificial, UNED, Juan del Rosal 16, 28040 Madrid, Spain
⁷ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, B5C, 4000 Sart Tilman, Belgium
⁸ Centre de Recherche en Astronomie, Astrophysique et Géophysique, Route de l’Observatoire, BP 63 Bouzareah, 16340 Algers, Algeria
⁹ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, 15783 Athens, Greece
¹⁰ Osservatorio Astrofisico di Torino, Istituto Nazionale di Astrofisica (INAF), 10025 Pino Torinese, Italy
¹¹ Royal Observatory of Belgium, 3 avenue circulaire, 1180 Brussels, Belgium
¹² Area of Languages and Computer Systems, Pablo de Olavide University, 41013 Seville, Spain
¹³ Observatoire de Paris, GEPI, CNRS UMR 8111, 92195 Meudon, France
¹⁴ Institut de Physique de Rennes, Université de Rennes 1, CNRS UMR 6251, 35042 Rennes, France
¹⁵ Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
¹⁶ Centre National d’Études Spatiales, 18 Av. Edouard Belin, 31401 Toulouse, France
¹⁷ Niels Bohr Institute, Copenhagen University, 2100 Copenhagen, Denmark
¹⁸ Tartu Observatory, 61602 Toravere, Estonia
¹⁹ Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Universitá di Catania, via S. Sofia 78, Catania, Italy
²⁰ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, Catania, Italy
²¹ CSC Danmark A/S, Retortvej 8, 2500 Valby, Denmark
²² European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile
²³ Institut d’Astrophysique de Paris, UMR 7095 CNRS – Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
²⁴ Université de Paris-Sud XI, IAS, 91405 Orsay Cedex, France
²⁵ INAF – Osservatorio Astronomico di Padova, 35122 Padova, Italy
²⁶ LAB UMR 5804, Univ. Bordeaux – CNRS, 33270 Floirac, France

Received: 23 July 2013
Accepted: 9 September 2013

Abstract

The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Itsmain objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaia’s unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite’s data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (rms residuals) on F, G, K, M dwarfs and giants at G = 15 (V = 15–17) for a wide range of metallicites and interstellar extinctions of around 100 K in effective temperature (T_eff), 0.1 mag in extinction (A₀), 0.2 dex in metallicity ([Fe/H]), and 0.25 dex in surface gravity (log g). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in December 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data.