Accurate characterization of the errors in the global astrometric solution for Gaia isessential for making optimal use of the catalogue data. We investigate the structure ofthe covariance between the estimated astrometric parameters by studying the properties ofthe astrometric least squares solution. We find that astrometric errors can be separatedin a star and an attitude part, due to the estimation of the star and attitude parametersrespectively. Hence the covariances can be separated in a star, an attitude and a crossterm. This is demonstrated using our scalable simulation tool AGISLab, where thecovariances are estimated statistically using Monte Carlo techniques.

We report on recent new developments around the Astrometric Global Iterative Solutionsystem. This includes the availability of an efficient Conjugate Gradient solver and theGeneric Astrometric Calibration scheme that had been proposed a while ago. The number ofprimary stars to be included in the core solution is now believed to be significantlyhigher than the 100 Million that served as baseline until now. Cloud computing servicesare being studied as a possible cost-effective alternative to running AGIS on dedicatedcomputing hardware at ESAC during the operational phase.

The Gaia space satellite will perform absolute astrometry, aiming at the definition of aglobal astrometric reference frame at visual wavelengths. Within this reference system, itwill be very difficult to identify possible errors in the measurements or in the datareduction process that brings about the definition of the final catalogue. The Gaia DataProcessing and Analysis Consortium (DPAC) has established an Astrometric Verification Unit(AVU) to verify crucial steps in the baseline data processing chain and report on anysignificant difference. This process is essential in order to guarantee a high qualitycatalogue to the larger scientific community. We describe here the global spherereconstruction (GSR) component of AVU hosted by the Italian data processing centre atTorino (DPCT).

The core data reduction for the Nano-JASMINE mission is planned to be done with Gaia’sAstrometric Global Iterative Solution (AGIS). The collaboration started at 2007 promptedby Uwe Lammers’ proposal. In addition to similar design and operating principles of thetwo missions, this is possible thanks to the encapsulation of all Gaia-specific aspects ofAGIS in a Parameter Database. Nano-JASMINE will be the test bench for Gaia AGIS software.We present this idea in detail and the necessary practical steps to make AGIS work withNano-JASMINE data. We also show the key mission parameters, goals, and status of the datareduction for the Nano-JASMINE.

The SIM-Lite mission has finished its technology programme and continues with anengineering risk reduction activity while waiting for the results of the 2010 decadalreview. One of the last remaining activities is work on the SCDU testbed, which isdesigned to calibrate the spectral bias in interferometric astrometry to 0.1 microarcsec.This talk will provide a summary of engineering activities on building flight-likeprototypes of the key interferometer subassemblies, as well as an overview of the types ofproblems one encounters when attempting to do astrometry below 1 microarcsec, as well astheir solution.

The Origins Billions Star Survey (OBSS) is a space astrometry mission that was funded byNASA in 2004 to perform an eight-month concept study. Although the OBSS mission was notselected for further development beyond the concept study phase, OBSS spawned asmaller-scale mission, called the Joint Milli-Arcsecond Pathfinder Survey (JMAPS), whichis currently funded for launch in early 2014. JMAPS is a small, space-based, all-skyvisible wavelength astrometric and photometric survey mission for 0th through 14th magnitudestars. The primary objective of the JMAPS mission is the generation of an astrometric starcatalogue with better than 1 milliarcsecond positional accuracy and photometry to the 1%accuracy level, or better, at 1st to 12th magnitude.

We present the pipeline processing (for photometry and spectrophotometry) primarily based on the comparison of the observation with a prediction from the spectral energy distribution and total flux of the source and a set of parameters modelling the instrument properties observation-to-observation. Experiments on G white light calibration yield residuals well below one mmag for most of the cases, but for extreme colour stars. For blue and red spectra, tests up to now yield residuals significantly smaller than the observational noise, except for sources with very strong spectral features, which present flux residuals of 2–3% in the spectral lines (at G = 15). Work continues to account for all instrumental effects, to add complexity to the instrument model and to improve the processing pipeline.

The Gaia spectro-photometric data consist of white-light G magnitudes from unfilteredfluxes measured in the astrometric field CCDs, and low resolution prism spectra measuredin the blue (BP) and red (RP) CCDs. The integrated flux of these BP and RP spectra willyield GBP and GRP magnitudes astwo broad passbands. The internal flux calibration will correct for all possibleinstrumental effects and produce mean spectral energy distributions in an internallydefined flux scale. The purpose of the absolute flux calibration is to tie this flux scaleto physical units by means of spectro-photometric standard stars that rely ultimately onVega’s absolute flux scale. The characteristics of the Gaia spectrophotometric system willbe described, and the absolute calibration process will be outlined and compared withexamples of classical systems.

The ESA Gaia mission will provide a multi-epoch database for a billion of objects,including variable objects that comprise stars, active galactic nuclei and asteroids. Wehighlight a few of Gaia’s properties that will benefit the study of variable objects, andillustrate with two examples the work being done in the preparation of the data processingand object characterization. The first example relates to the analysis of the nearlysimultaneous multi-band data of Gaia with the Principal Component Analysis techniques, andthe second example concerns the classification of Gaia time series into variability types.The results of the ground-based processing of Gaia’s variable objects data will be madeavailable to the scientific community through the intermediate and final ESA releasesthroughout the mission.

Our goal is to assess Gaia’s performance on the period recovery of short period(p < 2 hours) and small amplitude variability. To reach thisgoal first we collected the properties of variable stars that fit the requirementsdescribed above. Then we built a database of synthetic light-curves with short period andlow amplitude variability with time sampling that follows the Gaia nominal scanning lawand with noise level corresponding to the expected photometric precision of Gaia. Finallywe performed period search on the synthetic light-curves to obtain period recoverystatistics. This work extends our previous period recovery studies to short periodvariable stars which have non-stationary Fourier spectra.

Synoptic sky surveys are opening up exciting opportunities in time domain astronomy. Gaiawill make a great contribution to this field. A crucial factor for good scientific returnsis real-time classification of transients, in order to optimize their follow-up. We havebeen developing infrastructure towards this end starting from the completed Palomar-Quest(PQ) survey, and the ongoing Catalina Real-Time Transient Survey (CRTS). CRTS has beenconsistently producing transients for almost three years now. We describe here the effortsrelated to transient classification and event dissemination. Many of the technologies andmethodologies we are developing may benefit Gaia.

The lack of radial velocity data in the Hipparcos catalogue was considered a significantdeficiency, so when Gaia was conceived, a spectrometer was a core constituent of itspayload. The Gaia Radial Velocity Spectrometer faced a number of design challenges, inparticular set by the need to balance kinematic and astrophysical capability. We presentan overview of the evolution of the instrument to its present form, identifying thecompeting technical, performance and programmatic factors which have shaped it.

During the five years of the mission, the Gaia spectrograph, the Radial Velocity Spectrometer (RVS) will repeatedly survey the celestial sphere down to magnitude V ~ 17–18. This talk presents: (i) the system which is currently developed within the Gaia Data Processing and Analysis Consortium (DPAC) to reduce and calibrate the spectra and to derive the radial and rotational velocities, (ii) the RVS expected performances and (iii) scientific returns.

The calibration of the Radial Velocity Zero-Point (RVZP) of the Radial VelocitySpectrometer (RVS) will be performed with the help of Radial Velocity (RV) standard starsand asteroids. A full-sky list of RV standard stars candidates has been built for thispurpose within the Development Unit (DU) 640 of the Gaia DPAC Consortium. A ground-basedcampaign of RV observations has been initiated to eliminate unsuitable candidates.Simulations have also been performed in order to estimate in advance the number of RVstandard stars and asteroids crossing the RVS field of view. These standard stars andasteroids will also be very helpful for controlling any harmful effect (especially the CCDradiation damage) on calibration and RVZP during the lifetime of the Gaia project.Kinematic RV are expected to be published at the end of the project for the brighteststars, taking into account gravitational redshift and convective shifts for the linespresent in the RVS spectral wavelength range.

The growing awareness of the importance of the fossil record in the Milky Way forconstraining galaxy formation theory is reflected by the increasing number of new ground-and space-based surveys designed to unravel the formation history of the Galaxy. Recently,a new kinematic survey has been produced by means of spectro-photometric data from theSloan Digital Sky Survey (SDSS-DR7) and high-quality proper motions derived frommultiepoch positions from the Guide Star Catalogue II (GSC-II). In this framework, weassembled a sample of ~ 30 000 FGK nearby metal-poor (sub)dwarfs for whichselection and distance estimates take advantage of accurate stellar atmospheric parameters(effective temperature, surface gravity and metallicity) derived from SDSS spectra. Here,as one of the most interesting applications of this catalogue, we consider the feasibilityof probing fossil signatures of the formation of the Milky Way by selecting and analysingsubsamples of stars as tracers of the seven-dimensional space distribution (fullphase-space coordinates plus chemical abundance) of the Galactic halo population within afew kiloparsecs from the Sun. Preliminary results exhibit statistical evidence fordiscrete overdensities localised in kinematics and in the space of adiabatic invariants(angular momentum and energy). By examination of their intrinsic properties, we suggestthat they may be possible fossil signatures of past mergers or other accretion events.

The automated stellar classification algorithm, MATISSE, has been developed at theObservatoire de la Côte d’Azur (OCA) as a means of determining stellar effectivetemperatures, surface gravities and chemical abundances for large samples of stellarspectra. MATISSE is one of the key programmes to be used in the analysis of the spectrathat will be obtained by the Radial Velocity Spectrometer (RVS) on the European SpaceAgency’s (ESA) Gaia satellite. In preparation for the Gaia mission, rigorous testing ofMATISSE is currently being carried out using large datasets of spectra from the EuropeanSouthern Observatory (ESO) archive (The AMBRE Project, a collaboration between ESO andOCA). The derived stellar parameters will be delivered to ESO in order to make themavailable to the astronomical community via the Virtual Observatory. This paper presentsthe preliminary results of the analysis of the archived FEROS spectra.

I discuss wide-field high resolution spectroscopic instruments in the context of Gaia andGalactic archaeology. Galactic archaeology aims to discover signatures or fossils from theepoch of Galaxy formation, to give observational insights into the processes which tookplace as the Galaxy was assembled. Chemical tagging based on large high resolutionspectroscopic surveys will soon become a significant part of Galactic archaeology. Much ofthe discussion is focussed on prospects for the new HERMES instrument on the AAT.

We have chosen the name of GYES, one of the mythological giants with one hundred arms,offspring of Gaia and Uranus, for our instrument study of a multifibre spectrograph forthe prime focus of the Canada-France-Hawaii Telescope. Such an instrument could provide anexcellent ground-based complement for the Gaia mission and a northern complement to theHERMES project on the AAT. The CFHT is well known for providing a stable prime focusenvironment, with a large field of view, which has hosted several imaging instruments, buthas never hosted a multifibre spectrograph. Building upon the experience gained at GÉPIwith FLAMES-Giraffe and X-Shooter, we are investigating the feasibility of a highmultiplex spectrograph (about 500 fibres) over a field of view one degree in diameter. Weare investigating an instrument with resolution in the range 15 000 to 30 000, whichshould provide accurate chemical abundances for stars down to 16th magnitude and radialvelocities, accurate to 1 km s-1 for fainter stars. The study is led byGÉPI-Observatoire de Paris with a contribution from Oxford for the study of thepositioner. The financing for the study comes from INSU CSAA and Observatoire de Paris.The conceptual study will be delivered to CFHT for review by October 1st 2010.

Gaia will also provide a comprehensive survey of Solar System objects. If compared toother large ground-based surveys, Gaia potential for discoveries of small asteroidsappears to be limited by its magnitude threshold for detection. However, it can providevaluable data on the physical properties of the observed objects. If compared to LSST,Pan-STARRS or other surveys Gaia is complementary and occupies a clearly definedniche on its own.

Statistical asteroid-orbit-computation methods have proven important for applicationssuch as computing the collision probability, performing dynamical classification,identifying asteroids, and aiding the recovery of lost objects. These methods will be ofmajor importance during the Gaia mission (to be launched in 2012). Here we discuss thesemethods and some of their applications and potentials. As earlier, we examine the Bayesiana posteriori probability density of the orbital elements using Monte-Carlo methods thatmap the discretized volume of solutions in the orbital-element phase space. In particular,we use the Markov-chain Monte-Carlo (MCMC) method to map the phase space. The marginalorbital-element distributions then serve as a base for applications as collisionprobability computation, dynamical classification and others. A number of recentapplications are presented. Importance of the method for the Gaia mission is alsodescribed.