The nature and origin of the Galactic warp represent one of the open questions posed by Galactic evolution. Thanks to Gaia high precision absolute astrometry, steps towards the understanding of the warp's dynamical nature can be made. Indeed, proper motions for long-lived stable warp are expected to show measurable trends in the component vertical to the galactic plane. Within this context, we search for the kinematic warp signal in the first Gaia data release (DR1). By analyzing distant spectroscopically-identified OB stars in the Hipparcos subset in Gaia DR1, we find that the kinematic trends cannot be explained by a simple model of a long-lived warp. We therefore discuss possible scenarios for the interpretation of the obtained results. We also present current work in progress to select a larger sample of OB star candidates from the Tycho-Gaia Astrometric Solution (TGAS) subsample in DR1, and delineate the points that we will be addressing in the near future.

We have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, AqC4, produced by a cosmological simulation integrating a sub-resolution ISM model. We evidence a global inside-out and upside-down disk evolution, that is consistent with a scenario where the “thin disk” stars are formed from the accreted gas close to the galactic plane, while the older “thick disk” stars are originated in situ at higher heights. Also, the bar appears the most effective heating mechanism in the inner disk. Finally, no significant metallicity-rotation correlation has been observed, in spite of the presence of a negative [Fe/H] radial gradient.

We examine the evolution induced by secular processes of an initial, cosmologically motivated, radial chemical distribution, in a barred and an unbarred disk.

We report on the effect of observational errors when recovering cold streams related to the formation of our Galaxy by analysing the 10% fastest objects within 3 kpc of the “Sun” of an inner halo based on four N− body numerical simulations of the interaction between dwarf galaxies and the Milky Way. Much of the original substructure becomes visible again thanks to the superior precision that Gaia will achieve.

Although the thick disk in our Galaxy was revealed more than thirty years ago, its formation scenario is still unclear. Here, we analyze a chemo-dynamical simulation of a primordial disk population representative of the Galactic thick disk and investigate how the spatial, kinematic, and chemical properties are affected by the presence of a central bar.

We report on the discovery and characterization of a possibly new signature related to the formation of the Milky Way stellar local halo.

Most of the discovered exoplanets are close to our sun. Usually their host star is with large proper motions, which is an important parameter for exoplanet searching. The first version of absolute proper motions catalog achieved based on Digitized Sky Survey Schmidt plate where outside the galactic plane |b|≥27° is presented, resulting in a zero point error less than ± 0.3 mas/yr, and the overall accuracy better than ± 4.5 mas/yr for objects brighter than RF=18.5, and ranging from 4.5 to 9.0 mas/yr for objects with magnitude 18.5<RF<20.5. The systematic errors of absolute proper motions related to the position, magnitude and color are practically all removed. The sky cover of this catalog is 22,525 degree2, the mean density is 6444 objects/degree2 and the magnitude limit is around RF=20.5.

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.

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.

To make GSC-II more accurate and useful, it is necessary to re-calibrate GSC-II when a better reference catalogue (UCAC2) is available. With UCAC2 as the reference, preliminary re-calibration of some sample plates from GSC2.3 were carried out with different methods, such as Global, Mask and Filter. The results indicate that a 7th-order polynomial is sufficient to account for the influence of Schmidt plate deformation on the measured coordinates of stars. The magnitude equation can be eliminated after correcting for a common magnitude equation. The RMS of the re-calibrated data is around ±0.2~0.3 arcsec.

In this paper, we first summarize the results of a large-scale double-blind tests campaign carried out for the realistic estimation of the Gaia potential in detecting and measuring planetary systems. Then, we put the identified capabilities in context by highlighting the unique contribution that the Gaia exoplanet discoveries will be able to bring to the science of extrasolar planets during the next decade.

The GSC 2.3 is a current catalog release extracted from the Guide Star Catalog II database, which is maintained at the Space Telescope Science Institute in Baltimore, USA. The catalog contains astrometry, multi-band photometry (BJ, RJ, IN) and star/non-star classification for 945,592,683 objects down to the magnitude limit of the survey plates. We review the performance of stellar parameters, anticipating the improvements in astrometric accuracy foreseen by its recalibration with the newly available catalog in the UCAC series.

Heliocentric (UVW) and galactocentric (VR VΦ VZ) space motions were derived for 38 RR Lyrae (RRL) and 79 blue horizontal branch (BHB) stars in a 200-sq degree area near the North Galactic Pole (NGP). A kinematic analysis of the 26 RRL and 52 BHB stars whose height (Z) above the plane is < 8 kpc shows that the sample is not homogeneous. Our BHB sample shows zero galactic rotation and roughly isotropic velocity dispersions. whereas the RRL sample shows a definite retrograde rotation and non-isotropic velocity dispersions. The combined BHB and RRL sample shows a smaller retrograde rotation that is similar to that found by Majewski et al. (1996) for a sample of subdwarfs in SA 57 at the NGP. There are significantly more RRL with negative W-velocity (streaming down) than positive W-velocity, whereas the numbers of BHB stars are comparable. This indicates the presence near the NGP of an accreted halo component that is rich in RRL (probably Oosterhoff type I) stars.

These results are presented in detail in a forthcoming paper (Kinman et al. 2007).

We explore the stellar halo of the Milky Way to search for fossil signatures of past mergers. We use the Beers et al. (2000) catalog of non-kinematically selected metal poor stars in the solar neighborhood to select subsets of halo stars within 1-2 kpc of the Sun. Motivated by the results of high resolution CDM simulations, we look for substructure in the kinematics of the fastest stars. When a two-point velocity correlation function is applied to these subsets, statistical evidence of substructure is found. This appears to be due to a small moving group with dynamical properties similar to the stellar “stream” previously discovered by Helmi et al. (1999).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Microlensing experiments have suggested that a significant part of the dark halo of the Milky Way could be composed of matter in the form of massive compact halo objects (MACHOs). Cool ancient white dwarfs (WDs) are the natural candidates. Here we present a new survey of halo WDs and evaluate the local space density using an accurate kinematic analysis. A comparison to a revaluation of the Oppenheimer et al. result is also provided. the local space density estimated for the two independent samples is about ~ 10–5M⊙ pc–3.

Magnetization measurements were performed as a function of magnetic field H and temperature T on samples of nine different materials including clear fused quartz, cartridge brass, G-10 glass-reinforced epoxy, acetal homopolymer, glass-filled acetal, phenolic, and other plastics. A small yet distinct amount of ferromagnetic or paramagnetic impurities is observed in all the materials investigated in this study except quartz. In contrast, the magnetic response of quartz is typical of a diamagnet over the temperature range 5 K to 300 K. The volume susceptibility is equal to −4.4×10−7 (cgs) over the whole temperature range.

New GSC-II proper motions of RR Lyrae and Blue Horizontal Branch (BHB) stars near the North Galactic Pole are used to show that the Galactic Halo 5 kpc above the Plane has a significantly retrograde galactic rotation.

The ESA Cornerstone Mission GAIA, to be launched prior to 2012 and with a nominal lifetime of 5 years, will improve the accuracy of Hipparcos astrometry by more than two orders of magnitude. GAIA high-precision global astrometric measurements will provide deep insights on the science of extra-solar planets. The GAIA contribution is primarily understood in terms of the number and spectral type of targets available for investigation, and characteristics of the planets to be searched for. Several hundreds of thousands of solar-type stars (F-G-K) within a sphere of ~200 pc centered on our Sun will be observed. GAIA will be particularly sensitive to giant planets (MP ~ MJ) on wide orbits, up to periods twice as large as the mission duration, the potential signposts of the existence of rocky planets in the Habitable Zone. Thousands of new planets might be discovered, and a significant fraction of those which will be detected will have orbital parameters measured to better than 30% accuracy. By measuring to a few degrees the relative inclinations of planets in multiple systems with favorable configurations, GAIA will also make measurements of unique value towards a better understanding of the formation and evolution processes of planetary systems.

Faint surveys of accurate colors and proper motions are fundamental for studying the physical and kinematical properties of the stellar populations in the Galaxy. A program designed to address such issues has been initiated on selected fields utilizing prototype material from the GSC-II project (see McLean et al. in this volume, p. 431). Photographic photometry V, B–V, V–Rc, is derived down to V = 18.5 with a precision of about 0.1 mag, together with absolute proper motions to σμ ≃ 3 mas/yr.