The Future of Stellar Populations Studies in the Milky Way and the Local Group

The last decade has seen enormous progress in understanding the structure of the Milky Way and neighboring galaxies via the production of large-scale digital surveys of the sky like 2MASS and SDSS, as well as specialized, counterpart imaging surveys of other Local Group systems. Apart from providing snaphots of galaxy structure, these "cartographic" surveys lend insights into the formation and evolution of galaxies when supplemented with additional data (e.g., spectroscopy, astrometry) and when referenced to theoretical models and simulations of galaxy evolution. These increasingly sophisticated simulations are making ever more specific predictions about the detailed chemistry and dynamics of stellar populations in galaxies. To fully exploit, test and constrain these theoretical ventures demands similar commitments of observational effort as has been plied into the previous imaging surveys to fill out other dimensions of parameter space with statistically significant intensity. Fortunately the future of large-scale stellar population studies is bright with a number of grand projects on the horizon that collectively will contribute a breathtaking volume of information on individual stars in Local Group galaxies.Comment: 12 pages, 0 figures, IAU Symposium No. 262, Stellar Populations - Planning for the Next Decad

Prospects for Gaia and other space-based surveys

Gaia is a fully-approved all-sky astrometric and photometric survey due for launch in 2011. It will measure accurate parallaxes and proper motions for everything brighter than G=20 (ca. 10^9 stars). Its primary objective is to study the composition, origin and evolution of our Galaxy from the 3D structure, 3D velocities, abundances and ages of its stars. In some respects it can be considered as a cosmological survey at redshift zero. Several other upcoming space-based surveys, in particular JWST and Herschel, will study star and galaxy formation in the early (high-redshift) universe. In this paper I briefly describe these missions, as well as SIM and Jasmine, and explain why they need to observe from space. I then discuss some Galactic science contributions of Gaia concerning dark matter, the search for substructure, stellar populations and the mass--luminosity relation. The Gaia data are complex and require the development of novel analysis methods; here I summarize the principle of the astrometric processing. In the last two sections I outline how the Gaia data can be exploited in connection with other observational and theoretical work in order to build up a more comprehensive picture of galactic evolution.Comment: To appear in the proceedings of the JD13 "Exploiting large surveys for Galactic astronomy" held at the IAU GA 2006, Prague. 9 page

Inversion formula for determining parameters of an astrometric binary

It is believed that some numerical technique must be employed for the determination of the system parameters of a visual binary or a star with a planet because the relevant equations are not only highly nonlinear but also transcendental owing to the Kepler's equation. Such a common sense, however, is not true; we discover an analytic inversion formula, in which the original orbital parameters are expressed as elementary functions of the observable quantities such as the location of four observed points and the time interval between these points. The key thing is that we use the time interval but not the time of each observation in order to avoid treating the Kepler's equation. The present formula can be applied even in cases where the observations cover a short arc of the orbit during less than one period. Thus the formula will be useful in the future astrometric missions such as SIM, GAIA and JASMINE.Comment: 8 pages; accepted for publication in PAS