We have written a theoretical description of one-way and two-way satellite time and frequency transfer and developed a model of the micro-wave link in the frame of the ACES/PHARAO mission. This is used to write a data analysis software and a simulation to test it. A very short description of the mission and of the micro-wave link is given here. A detailed description can be found in Delva et al., 2012, Proceedings of the EFTF, Gothenburg, Sweden, arXiv:1206.6239.

Since January 1st, 2010, the IAU (International Astronomical Union) fundamental celestial reference frame has been the 2nd International Celestial Reference Frame (ICRF2), which is composed of Very Long Baseline Interferometry (VLBI) positions for more than 3000 extragalactic radio sources. This frame is constantly improving through joint efforts of the VLBI community. By surveying the whole sky up to magnitude 20, the European space astrometric mission Gaia will soon create its own celestial reference frame directly in the optical domain and with many more sources. By 2015–2020, the two frames will thus cohabit and it will be important to align these to the highest accuracy for consistency between optical and radio positions. In this paper, we present the various observational approaches that are undertaken to improve the VLBI frame in the future. These include extension to weaker sources for densification, extension to higher radio frequencies to take advantage of the more compact morphology of the sources at these frequencies, and further observations in the southern hemisphere for homogeneous sky coverage. We also elaborate on how such future radio frames should contribute to highly-precise alignment between the VLBI and Gaia frames within the next decade.

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 for the prime focus of the Canada-France-Hawaii Telescope. Such an instrument could provide an excellent ground-based complement for the Gaia mission and a northern complement to the HERMES project on the AAT. The CFHT is well known for providing a stable prime focus environment, with a large field of view, which has hosted several imaging instruments, but has never hosted a multifibre spectrograph. Building upon the experience gained at GÉPI with FLAMES-Giraffe and X-Shooter, we are investigating the feasibility of a high multiplex spectrograph (about 500 fibres) over a field of view one degree in diameter. We are investigating an instrument with resolution in the range 15 000 to 30 000, which should provide accurate chemical abundances for stars down to 16th magnitude and radial velocities, accurate to 1 km s-1 for fainter stars. The study is led by GÉPI-Observatoire de Paris with a contribution from Oxford for the study of the positioner. 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 to other large ground-based surveys, Gaia potential for discoveries of small asteroids appears to be limited by its magnitude threshold for detection. However, it can provide valuable 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 defined niche on its own.

Gaia is the sixth cornerstone of the ESA Scientific Programme. Beginning 2006, the programme implementation phase was kicked off at Astrium Satellites. At summer 2010 all Critical Design Reviews of the modules have been passed successfully, which enables to give a good snapshot of the development progress. This presentation summarizes the history of the satellite programme. The status of the current development will be presented with a focus of the main challenging equipment, with a particular insight on the payload.

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 Gaia space astrometric mission will construct its own celestial reference frame based on thousands of QSO positions measured with an accuracy of a few tens of microarcseconds. For consistency with the current realization of the International Celestial Reference Frame, which is based on Very Long Baseline Interferometry (VLBI) positions for more than 3000 extragalactic radio sources, it is crucial that the two frames be aligned with the highest possible accuracy. This alignment requires a number of common objects with excellent optical and radio astrometric properties. Because of their physical properties, it is possible that the QSO optical and radio positions do not physically coincide at the 100 microarcsecond level. While such shifts may affect the accuracy in aligning the two frames, they may also help gaining insights into the physical conditions in the nuclear regions of these objects. This paper reviews the ongoing work to align the VLBI and Gaia frames along with the potential astrophysical outcome that may result from comparing/combining ultra-accurately these two frames.

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

Thick disks have been observed in many disk galaxies and our Galaxy, the Milky Way, also presents a thick disk whose main spatial, kinematic, and chemical features of this population are well established. However, the origin of this ancient component is still unclear in spite the many studies carried out and several formation scenarios proposed until now. For the first time to our knowledge, we found evidence of a kinematics-metallicity correlation, of about 40–50 km s-1 per dex, amongst thick disk stars at 1 kpc  < |z| < 3 kpc and with abundance −1 <[Fe/H]< −0.5. This finding sets important constraints on the origin of the thick disk in the context of CDM hierarchical galaxy formation mechanisms and of secular evolutionary processes in galactic disks. This result is reported and, preliminary results, based on new N-body high numerical resolution simulations of stellar disks endowed with a bulge inside a dark matter NFW halo, are presented.

A spectroscopic survey of nearly 700 stars probing the Galactic Thick Disc far from the Solar neighbourhood is performed. The MATISSE (MATrix Inversion for Spectral SynthEsis) algorithm is developed and trained in order to automatically obtain atmospheric parameters of stars. The derived effective temperatures, surface gravities and overall metallicities are then combined to stellar evolution isochrones, radial velocities and proper motions to derive the distances, kinematics and orbital parameters of the sample stars. Results are compared with simulations from the Besançon model of the Milky Way.

Companions exert adverse effects on the relationships valid for Cepheids. Physical companions may also cause observable effects (e.g., phase jump in the pulsation, slight excitation of non-radial modes). Many new binaries among Cepheids can be revealed by using radial velocity measurements to be made by Gaia and by deriving astrometric orbit from data to be obtained over the five years of the Gaia mission.

Cluster membership of Cepheids also facilitates the calibration of the period-luminosity relationship independently of the pulsation. A brief summary on the membership of Cepheids in clusters is also given.

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. We highlight a few of Gaia’s properties that will benefit the study of variable objects, and illustrate with two examples the work being done in the preparation of the data processing and object characterization. The first example relates to the analysis of the nearly simultaneous multi-band data of Gaia with the Principal Component Analysis techniques, and the 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 made available to the scientific community through the intermediate and final ESA releases throughout the mission.

By means of N-body simulations, we have investigated the impact of minor mergers on the angular momentum content and kinematical properties of a disc galaxy. Our simulations cover a range of initial orbital characteristics and the system consists of a massive galaxy with a bulge and a stellar disc merging with a much less massive gasless companion. Our results show that: (1) during the process of merging, the disc of the primary galaxy becomes kinematically hotter and thicker; (2) its specific angular momentum always decreases, independent of the orbit or morphology of the satellite galaxy; (3) the decrease in the rotation velocity of the primary galaxy is accompanied by a change in the anisotropy of the stellar orbits, which becomes increasingly radially dominated as the merger advances; (4) the radial velocity dispersion increases at all radii, but in particular in the outermost regions; (5) at the same time, the transverse velocity decreases throughout the whole disc, except in the inner region, where the constribution of bulge stars leads to an increase of σt.

The calibration of the Radial Velocity Zero-Point (RVZP) of the Radial Velocity Spectrometer (RVS) will be performed with the help of Radial Velocity (RV) standard stars and asteroids. A full-sky list of RV standard stars candidates has been built for this purpose within the Development Unit (DU) 640 of the Gaia DPAC Consortium. A ground-based campaign of RV observations has been initiated to eliminate unsuitable candidates. Simulations have also been performed in order to estimate in advance the number of RV standard stars and asteroids crossing the RVS field of view. These standard stars and asteroids will also be very helpful for controlling any harmful effect (especially the CCD radiation 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 brightest stars, taking into account gravitational redshift and convective shifts for the lines present in the RVS spectral wavelength range.

During its mission Gaia will give access to a so far never reached astrometric accuracy of a large number of Solar System objects. Nevertheless some of these Gaia observations could be efficiently completed by ground-based observations. This will allow us to get a better understanding of the dynamical and physical properties of these objects. We present a general overview of these cases.

Classification and parametrization of unresolved galaxies to be detected by Gaia is the goal of our contribution to DPAC/CU8. Gaia will observe more than several times 106 unresolved galaxies seen almost as point sources. For the classification and parametrization of these sources we have undertaken the following tasks: a) providing libraries of synthetic galaxy spectra (produced under the PÉGASE.2 code of galaxy evolution) and a semi-empirical library using observed galaxy spectra from SDSS data archive. b) Developping an appropriate algorithm called Unresolved Galaxy Classifier (UGC). The algorithm is being developed implementing the Support Vector Machines (SVM), a supervised training technique. This algorithm utilizes Gaia simulated BP/RP galaxy spectra of our synthetic galaxy library.

In this study we use numerical N-body/SPH simulations to investigate the vertical stellar distribution of thick disks formed in minor mergers. These disks have a sech-shape vertical surface density profile which needs two sech functions with different scale heights to fit due to an additional stellar excesses at large heights (z ≳ 4 − 5 kpc). The scale heights of merger-induced thick disks increase with radius but the details of this thickening are sensitive to orbital configurations and gas fraction of the galaxies. The scale height of the stellar excess is constant with radius and largely independent of the initial conditions. The effects of minor mergers is cumulative in the sense that several minor mergers have the same impact of a single minor merger of the same total mass. Scattering by self-gravitating masses (clumps) in unstable gaseous disks can produce thick disks with constant scale height, however, there is not a stellar excess at large scale heights. Most of these results are found to be in good agreement with observations and thus we conclude that minor mergers remains a viable mechanism for the creation of galactic thick disks.

The growing awareness of the importance of the fossil record in the Milky Way for constraining 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 the Sloan Digital Sky Survey (SDSS-DR7) and high-quality proper motions derived from multiepoch positions from the Guide Star Catalogue II (GSC-II). In this framework, we assembled a sample of ~ 30 000 FGK nearby metal-poor (sub)dwarfs for which selection 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 feasibility of probing fossil signatures of the formation of the Milky Way by selecting and analysing subsamples of stars as tracers of the seven-dimensional space distribution (full phase-space coordinates plus chemical abundance) of the Galactic halo population within a few kiloparsecs from the Sun. Preliminary results exhibit statistical evidence for discrete overdensities localised in kinematics and in the space of adiabatic invariants (angular momentum and energy). By examination of their intrinsic properties, we suggest that they may be possible fossil signatures of past mergers or other accretion events.

The high precision X-ray spectroscopy studies of plasma created from the CO2 clusters in gas jet targets by the ultrashort laser pulses (35 and 60 fs duration) were performed at the intensities IL ∼ 1017–1018 W cm−2. The spectral line shape of the H-like and He-like oxygen ions gains an asymmetry with increasing the laser pulse intensity. Theoretical modeling of the line shape shows that the asymmetry can be explained by absorption of the Doppler-shifted line radiation from the essential fraction of ions (over 10−3) with energies above 1 MeV due to photoionization of inner shells of carbon ions. The results obtained demonstrate measurement capabilities of the X-ray spectral measurements of multicharged ions accelerated during the interaction with a laser radiation.

Time-resolved photoemission spectroscopy, using high order harmonics, is used to measure the energy relaxation rate of hot electrons in α-SiO2 with sub-picosecond time resolution. Our results indicate that electrons of 30 eV kinetic energy in the conduction band relax at a rate which is at least two orders of magnitude lower than the one of photo-excited carriers of a few eV. As a result, we give insight in the relaxation process of hot electrons and show that impact ionization probability per unit time is only of the order of 1/40 ps−1, in very strong contrast with the much higher value generally assumed in models of optical breakdown.