As the title of this symposium implies, one of the aims is to examine the future of astrometry as we move from an era in which thanks to the Hipparcos Catalogue everyone has become familiar with milliarcsecond astrometry to an era in which microarcsecond astrometry will become the norm. I will take this look into the future by first providing an overview of present astrometric programmes and how they fit together and then I will attempt to identify the most promising future directions. In addition I discuss the important conditions for the maximization of the scientific return of future large and highly accurate astrometric catalogues; catalogue access and analysis tools, the availability of sufficient auxiliary data and theoretical knowledge, and the education of the future generation of astrometrists.

Highly accurate astrometry of asteroids in the frame of QSOs will provide the direct link between the Dynamical Reference Frame and the International Celestial Reference Frame. We propose a procedure that implies a selection of events for asteroids with accurately determined orbits crossing the CCD field containing the selected quasars. For asteroid ephemerides, a numerical integration method coupled with precise modelling of asteroid brightness will be used for analyzing our observations. A list of predictions for this type of “close approaches” will be presented.

Window functions describe, as a function of orbital period, the probability that an existing planetary transit is detectable in one's data for a given observing strategy. We show the dependence of this probability upon several strategy and astrophysical parameters, such as length of observing run, observing cadence, length of night, and transit duration. The ability to detect a transit is directly related to the intrinsic noise of the observations. In our simulations of the window function, we explicitly address non-correlated (white) noise and correlated (red) noise and discuss how these two different noise components affect window functions in different manners.

Tides come from the fact that different parts of a system do not fall in exactly the same way in a non-uniform gravity field. In the case of a protoplanetary disk perturbed by an orbiting, prograde protoplanet, the protoplanet tides raise a wake in the disk which causes the orbital elements of the planet to change over time. The most spectacular result of this process is a change in the protoplanet's semi-major axis, which can decrease by orders of magnitude on timescales shorter than the disk lifetime. This drift in the semi-major axis is called planetary migration. In a first part, we describe how the planet and disk exchange angular momentum and energy at the Lindblad and corotation resonances. Next we review the various types of planetary migration that have so far been contemplated: type I migration, which corresponds to low-mass planets (less than a few Earth masses) triggering a linear disk response; type II migration, which corresponds to massive planets (typically at least one Jupiter mass) that open up a gap in the disk; “runaway” or type III migration, which corresponds to sub-giant planets that orbit in massive disks; and stochastic or diffusive migration, which is the migration mode of low- or intermediate-mass planets embedded in turbulent disks. Lastly, we present some recent results in the field of planetary migration.

We used VLBI observations at 8.4 GHz between 1991 and 2005 to determine the motion of the RS CVn binary IM Pegasi (HR 8703), the guide star for the NASA/Stanford gyroscope relativity mission, Gravity Probe B (GP-B). The motion was determined relative to our primary reference, the core of the quasar 3C 454.3. The stability of this core was checked relative to two other extragalactic sources, B2250+194 and B2252+172, the former of which was tied to the ICRF. The core of 3C 454.3 is stationary relative to these two sources to within 30 μas yr−1 in each coordinate. IM Pegasi's radio morphology varies, but appears to be on average centered on the primary. We estimate the proper motion of IM Pegasi with a statistical standard error (sse) of 30 μas yr−1 in each coordinate. We also estimate the parallax with a statistical standard error of 75 μas and parameters of the orbit with sse's corresponding to 110 μas on the sky. Coupled with our upper limit of three times the sse on any systematic errors in each parameter %threefold higher upper limit on the systematic error contributions to each parameter estimate, these results ensure that the uncertainty of IM Pegasi's proper motion makes only a small contribution to the uncertainty of GP-B's tests of general relativity.

A new star catalog has been derived recently, which is based on combination of Hipparcos/Tycho Catalogues with long lasting ground-based astrometric observations. In addition to ‘classical’ mean positions and proper motions of the stars, it contains also information on periodic motions of many stars that are due to double or multiple stellar systems. The catalog, called EOC-3, contains 4418 different objects, out of which 585 have significant periodic motions. This improved catalog is used as a reference frame in optical wavelength to derive a new series of Earth Orientation Parameters. To this end, almost five million observations of latitude/universal time variations made at 33 observatories are used. The new EOP series covers almost the entire 20th century (namely the interval 1899.7-1992.0).

As the oldest objects whose ages can be accurately determined, Galactic globular clusters can be used to establish the minimum age of the universe (and hence, to constrain cosmological models) and to study the early formation history of the Milky Way. The largest uncertainty in the determination of globular cluster ages is the distance scale. The current uncertainty in the distances to globular clusters is ~ 6%, which leads to a 13% uncertainty in the absolute ages of globular clusters. I am the PI on a SIM-Planetquest key project to determine the distances of 21 globular clusters with an accuracy of ranging from 1 to 4%. This will lead to age determinations accurate to 5 − 9%. The mean age of the oldest, most metal-poor globular clusters will be determined with an accuracy of ±3%.

SIM will search for planets with masses as small as the Earth's orbiting in the ‘habitable zones’ around more than 100 of the nearest stars and could discover many dozen if Earth-like planets are common. With a planned “Deep Survey” of 100–450 stars (depending on desired mass sensitivity) SIM will search for terrestrial planets around all of the candidate target stars for future direct detection missions such as Terrestrial Planet Finder and Darwin. SIM's “Broad Survey” of 2100 stars will characterize single and multiple-planet systems around a wide variety of stellar types, including many now inaccessible with the radial velocity technique. In particular, SIM will search for planets around young stars providing insights into how planetary systems are born and evolve with time.

Ground-based optical/IR interferometers have provided strong support to the space-based astrometric mission Hipparcos ever since the Hipparcos instrument was in operation in 1989. Interferometric observations also produced critical corrections of orbital motion to many targets, including radio stars, which link the Hipparcos system to the International Celestial Reference Frame (ICRF). In particular, orbital parallax from interferometers confirmed the 10% bias of the Pleiades distance from Hipparcos, and thus avoids revision of classical astronomy. Significant offsets and errors of Hipparcos parallax introduced by binary jitters are demonstrated in this work. By comparing the Hipparcos results with long baseline interferometry and other techniques including spectroscopy, multi-color photometry, Main-Sequence fitting, light curve measurements, Lunar occultation, Fine Guidance Sensor, etc., systematic biases and uncertainties of Hipparcos parallaxes are investigated and analyzed. We have established good models for major error sources of Hipparcos parallax, such as zonal bias, binary jitters, and luminosity-dependent errors. The lessons learned from the systematic biases of Hipparcos parallax are valuable to future space missions like SIM and Gaia.

The advent of next-generation telescopes with very wide fields-of-view creates a need for deep and precise reference frames for astrometric calibrations. The Deep Astrometric Standards (DAS) program is designed to establish such a frame, by providing absolute astrometry at the 5–10 mas level in four 10 deg2 Galactic fields, to a depth of V=25. The source of our basic reference frame is the UCAC2 catalog, significantly improved by additional observations, and new VLBI positions of radio-loud and optically visible QSOs. We describe all the major steps in the construction of the DAS fields and provide the current status of this project.

Recently, it has been observed the extreme metal-poor stars in the Galactic halo, which must be formed just after Pop III objects. On the other hand, the first gas clouds of mass ∼ 106 M⊙ are supposed to be formed at z ∼ 10, 20, and 30 for the 1σ, 2σ and 3σ, where the density perturbations are assumed of the standard ΛCDM cosmology. Usually it is approximated that the distribution of the density perturbation amplitudes is gaussian where σ means the standard deviation. If we could apply this gaussian distribution to the extreme small probability, the gas clouds would be formed at z ∼40, 60, and 80 for the 4σ, 6σ, and 8σ where the probabilities are approximately 3 × 10−5, 10−9, and 10−15. Within our universe, there are almost ∼ 1016 (∼ 1022M⊙/106M⊙) clouds of mass 106M⊙. Then the first gas clouds must be formed around z ∼ 80, where the time is ∼ 20 Myr (∼ 13.7/(1 + z)3/2 Gyr). Even within our galaxy, there are ∼ 105 (∼ 1011M⊙/106M⊙) clouds, then the first gas clouds within our galaxy must be formed around z ∼ 40, where the time is ∼ 54 Myr (∼ 13.7/(1+z)3/2Gyr).

The evolution time for massive star (∼ 102M⊙) is ∼ 3 Myr and the explosion of the massive supernova distributes the metal within a cloud. The damping time of the supernova shock wave in the adiabatic and isothermal era is several Myr and stars of the second generation (Pop II) are formed within a free fall time ∼ 20 Myr. Even if the gas cloud is metal poor, there is a lot of possibility to form the planets around such stars. The first planetary systems could be formed within ∼ 6 × 107 years after the Big Bang in the universe. Even in our galaxies, the first planetary systems could be formed within ∼ 1.7 × 108 years. If the abundance of heavy elements such as Fe is small compared to the elements of C, N, O, the planets must be the one where the rock fraction is small. It is interesting to wait the observations of planets around metal-poor stars. For the panspermia theory, the origin of life could be expected in such systems.

The ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 7–25 μas range down to 15 mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 330–1000 nm wavelength range and, for the brighter stars, radial velocity measurements. The scientific case covers an extremely wide range of topics in galactic and stellar astrophysics, solar system and exoplanet science, as well as the establishment of a very accurate, dense and faint optical reference frame. With a planned launch around 2012 and an (extended) operational lifetime of 6 years, final results are expected around 2021. We give a brief overview of the science goals of Gaia, the overall project organisation, expected performance, and some key technical features and challenges.

As a result of failed star formation, brown dwarfs (BDs) do not reach the critical mass to ignite the fusion of hydrogen in their cores. Different from their low-mass stellar brothers, the red dwarfs, BDs cool down with their lifetime to very faint magnitudes. Therefore, it was only about 10 to 20 years ago that such ultracool objects began to be detected. Accurate astrometry can be used to detect them indirectly as companions to stars by the signature of the so-called astrometric wobble. Resolved faint BD companions of nearby stars can be identified by their common proper motion (CPM). A direct astrometric detection of the hidden isolated BDs in the Solar neighborhood is possible with deep high proper motion (HPM) surveys. This technique led to the discovery of the first free-floating BD, Kelu 1, and of the nearest BD, ε Indi B. Both were meanwhile found to be binary BDs. The astrometric orbital monitoring of ε Indi Ba+Bb, for which we know an accurate distance from the Hipparcos measurement of its primary, ε Indi A, will allow the determination of individual masses of two low-mass BDs. Hundreds of BDs have been identified for the last decade. Deep optical sky survey (SDSS) and near-infrared sky surveys (DENIS, 2MASS), played a major role in the search mainly based on colours, since BDs emit most of their light at longer wavelengths. However, alternative deep optical HPM surveys based on archival photographic data are not only sensitive enough to detect some of the nearest representatives, they do also uncover many of the rare class of ultracool halo objects crossing the Solar neighborhood at large velocities. SSSPM 1444, with the extremely large proper motion of 3.5 arcsec/yr, is one of the nearest among these subdwarfs with masses at the substellar boundary. We present preliminary parallax results for this and two other ultracool subdwarfs (USDs) from the Calar Alto Omega 2000 parallax program.

We have performed monitoring observations of the 3-mm flux density toward the Galactic center compact radio source Sgr A* with the ATCA since 2005 October. It has been found that during several observing epochs Sgr A* was quite active, showing significant intraday variation. Here we report the detection of an IDV in Sgr A* on 2006 August 13, which exhibits a 27% fractional variation in about 2 hrs.

Evidence suggesting an observable magnetic interaction between a star and its hot Jupiter (Porb < 7 days, a < 0.1 AU, Mpsini > 0.2 MJ) appears as a cyclic variation of stellar activity synchronized to the planet's orbit. HD 179949 has been observed almost every year since 2001. Synchronicity of the Ca II H & K emission with the orbit is clearly seen in four out of six epochs, while rotational modulation with Prot=7 days is apparent in the other two seasons. We observe a similar phenomenon on υ And, which displays rotational modulation (Prot=12 days) in September 2005, while in 2002 and 2003 variations appear to correlate with the planet's orbital period. This on/off nature of star-planet interaction (SPI) in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. The tentative correlation between this activity in the 13 stars we have observed to date and the ratio of Mpsini to the planet's rotation period, a quantity proportional to the hot Jupiter's magnetic moment, first presented in Shkolnik et al. (2005) remains viable. This work furthers the characterization of SPI, improving its potential as a probe of extrasolar planetary magnetic fields.

In this report, we present results of analytical and numerical calculations of evolution the axis of rotation of planets moving at very close orbits. We consider the evolution of the axis of rotation caused by tidal perturbations of a parent star and obtain estimates of the principal moment of inertia and the dynamical flattening for nine exoplanets. From analysis of evolutionary equations, we obtain the critical values of the kinetic momentum vector, , for different values of orbital eccentricity. We find a general tendency of vector to evolve to the direction perpendicular to the orbital plane.

The discovery of an increasing number of extrasolar planets (EPs) prompts the development of a planetary taxonomy. Such analysis, as in many other fields of research, is useful to identify groups of objects sharing similar traits. When applied to extrasolar planets, the taxonomy may provide a valid support for disentangling the role of the several physical parameters (semimajor axis, metallicity etc.) involved in the planetary formation processes and subsequent evolution. We present the state-of-the-art for exoplanets taxonomy obtained with hierarchical algorithms and the definition of robust clusters of planets (this is an update of the taxonomy published in Marchi 2007). The physical relevance of the exoplanet clusters along with their implications for the formation theories are also discussed. Finally, we comment on the future improvements of such analysis taking into account new algorithms and new input variables.

Spectra of FGK stars were selected from the SDSS–DR5 spectroscopic database to investigate the Age-Metallicity relation and the [Fe/H] and [α/Fe] vertical gradients in the Milky Way. Atmospheric parameters and [α/Fe] were derived by comparing synthetic and measured Lick/SDSS spectral indices. Results were checked and complemented by analyzing solar neighbourhood stars. Spectroscopic distances and ages were obtained for a subsample of ~2000 stars using theoretical isochrones via a Bayesian approach. The resulting Age-Metallicity diagram and the [Fe/H] and [α/Fe] vertical gradients are presented.

Measuring the proper motions and geometric distances of galaxies within the Local Group is very important for our understanding of its history, present state and future. Currently, proper motion measurements using optical methods are limited only to the closest companions of the Milky Way. However, given that VLBI provides the best angular resolution in astronomy and phase-referencing techniques yield astrometric accuracies of ≈ 10 micro-arcseconds, measurements of proper motions and angular rotation rates of galaxies out to a distance of ~ 1 Mpc are feasible. This paper presents results of VLBI observations in regions of H2O maser activity of the Local Group galaxies M33 and IC 10. Two masing regions in M33 are on opposite sides of the galaxy. This allows a comparison of the angular rotation rate (as measured by the VLBI observations) with the known inclination and rotation speed of the Hi gas disk leading to a determination of a geometric distance of 730 ± 100 ± 135 kpc. The first error indicates the statistical error of the proper-motion measurements, while the second error is the systematic error of the rotation model. Within the errors, this distance is consistent with the most recent Cepheid distance to M33. Since all position measurements were made relative to an extragalactic background source, the proper motion of M33 has also been measured. This provides a three dimensional velocity vector of M33, showing that this galaxy is moving with a velocity of 190 ± 59 km s−1 relative to the Milky Way. For IC 10, we obtain a motion of 215 ± 42 km s−1 relative to the Milky Way. These measurements promise a new handle on dynamical models for the Local Group and the mass and dark matter halo of Andromeda and the Milky Way.

The problem of determination of the orbital velocity of an astrometric satellite from its own observational data is studied. It is well known that data processing of microarcsecond-level astrometric observations imposes very stringent requirements on the accuracy of the orbital velocity of satellite (a velocity correction of 1.45 mm/s implies an aberrational correction of 1 μas). Because of a number of degeneracies the orbital velocity cannot be fully restored from observations provided by the satellite. Seven constraints that must be applied on a velocity parameterization are discussed and formulated mathematically. It is shown what part of velocity can be recovered from astrometric data using a combined fit of both velocity parameters and astrometric parameters of the sources. Numerical simulations show that, with the seven constraints applied, the velocity and astrometric parameters can be reliably estimated from observational data. It is also argued that the idea to improve the velocity of an astrometric satellite from its own observational data is only useful if a priori information on orbital velocity justifies the applicability of the velocity constraints. The proposed model takes into account only translational motion of the satellite and ignores any satellite-specific parameters. Therefore, the results of this study are equally applicable to both scanning missions similar to Gaia, and pointing ones like SIM, provided that enough sources were observed sufficiently uniformly.