Mario G. Lattanzi

Space-borne global astrometric surveys: the hunt for extrasolar planets

The proposed global astrometry mission GAIA, recently recommended within the context of ESAs Horizon 2000 Plus long-term scientific programme, appears capable of surveying the solar neighbourhood within ∼200xa0pc for the astrometric signatures of planets around stars down to the magnitude limit of V=17xa0mag, which includes late M dwarfs at 100xa0pc. n n n nRealistic end-to-end simulations of the GAIA global astrometric measurements have yielded the first quantitative estimates of the sensitivity to planetary perturbations and of the ability to measure their orbital parameters. Single Jupiter-mass planets around normal solar-type stars appear detectable out to 150xa0pc (V≤12xa0mag) with probabilities ≥50xa0per cent for orbital periods between ∼2.5 and ∼8xa0yr, and their orbital parameters are measurable with better than 30xa0per cent accuracy to about 100xa0pc. Jupiter-like objects (same mass and period as our giant planet) are found with similar probabilities out to 100xa0pc. n n n nThese first experiments indicate that the GAIA results would constitute an important addition to those that will come from the other ongoing and planned planet-search programmes. These data combined would provide a formidable testing ground on which to confront theories of planetary formation and evolution.

ABSOLUTE PROPER MOTIONS OUTSIDE the PLANE (APOP) - A STEP TOWARD the GSC2.4

We present a new catalog of absolute proper motions and updated positions derived from the same Space Telescope Science Institute digitized Schmidt survey plates utilized for the construction of Guide Star Catalog II. As special attention was devoted to the absolutization process and the removal of position, magnitude, and color dependent systematic errors through the use of both stars and galaxies, this release is solely based on plate data outside the galactic plane, i.e., vertical bar b vertical bar >= 27 degrees. The resulting global zero point error is less than 0.6 mas yr(-1), and the precision is better than 4.0 mas yr(-1) for objects brighter than R-F = 18.5, rising to 9.0 mas yr(-1) for objects with magnitudes in the range 18.5 < R-F < 20.0. The catalog covers 22,525 square degrees and lists 100,774,153 objects to the limiting magnitude of R-F similar to 20.8. Alignment with the International Celestial Reference System was made using 1288 objects common to the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths. As a result, the coordinate axes realized by our astrometric data are believed to be aligned with the extragalactic radio frame to within +/- 0.2 mas at the reference epoch J2000.0. This makes our compilation one of the deepest and densest ICRF-registered astrometric catalogs outside the galactic plane. Although the Gaia mission is poised to set the new standard in catalog astronomy and will in many ways supersede this catalog, the methods and procedures reported here will prove useful to remove astrometric magnitude-and color-dependent systematic errors from the next generation of ground-based surveys reaching significantly deeper than the Gaia catalog.

NPARSEC : NTT Parallaxes of Southern Extremely Cool objects. Goals, targets, procedures and first results

The discovery and subsequent detailed study of T dwarfs has provided many surprises and pushed the physics and modeling of cool atmospheres in unpredicted directions. Distance is a critical parameter for studies of these objects to determine intrinsic luminosities, test binarity and measure their motion in the Galaxy. We describe a new observational program to determine distances across the full range of T dwarf sub-types using the NTT/SOFI telescope/instrument combination. We present preliminary results for ten objects, five of which represent new distances.

General relativistic satellite astrometry - II. Modeling parallax and proper motion

The non-perturbative general relativistic approach to global astrometry introduced by de Felice et al. ([CITE]) is here extended to account for the star motions on the Schwarzschild celestial sphere. A new expression of the observables, i.e. angular distances among stars, is provided, which takes into account the effects of parallax and proper motions. This dynamical model is then tested on an end-to-end simulation of the global astrometry mission GAIA. The results confirm the findings of our earlier work, which applied to the case of a static (angular coordinates only) sphere. In particular, measurements of large arcs among stars (each measurement good to ~

Memberships and CM diagrams of young open clusters. I - NGC 225

100 mu

NEW SIGNATURES OF THE MILKY WAY FORMATION IN THE LOCAL HALO AND INNER-HALO STREAMERS IN THE ERA OF GAIA

arcsec, as expected for

The ray tracing analytical solution within the RAMOD framework. The case of a Gaia-like observer

Vsim17

49 new T dwarfs identified using methane imaging

mag stars) repeated over an observing period comparable to the mission lifetime foreseen for GAIA, can be modeled to yield estimates of positions, parallaxes, and annual proper motions good to ~

Relativistic Models for a GAIA-Like Astrometry Mission

15 mu

The Gaia mission: the dawn of Astrometric Cosmology? Status and prospects after 14 months of science operations

arcsec. This second round of experiments confirms, within the limitations of the simulation and the assumptions of the current relativistic model, that the space-born global astrometry initiated with Hipparcos can be pushed down to the 10 -5 arcsec accuracy level proposed with the GAIA mission. Finally, the simplified case we have solved can be used as reference for testing the limiting behavior of more realistic models as they become available.