The velocity-space distribution of the solar neighborhood stars shows complex substructures (moving groups) including the well-known Hercules stream. Recently, the Gaia observation revealed their detailed structures, but their origins are still in debate. We analyzed a high-resolution N-body simulation of a Milky Way (MW)-like galaxy. To find velocity-space distributions similar to that of the solar neighborhood stars, we used Kullback-Leibler divergence (KLD), which is a metric to measure similarities between probability distributions. The KLD analysis shows the time evolution and the spatial variation of the velocity-space distribution. Velocity-space distributions with small KLDs (i.e. high similarities) are frequently but not always detected around in the simulated MW. In the velocity-map with smallest KLD, the velocity-space substructures are made from bar resonances.

The age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR, primarily due to the difficulty in obtaining accurate ages for individual field stars. We have started an observational campaign for providing new observational input by using wide white dwarf-main sequence (WDMS) binaries. WDs are natural clocks and can be used to derive accurate ages. Metallicities can be obtained from the MS companions. Since the progenitors of WDs and the MS stars were born at the same time, WDMS provide a unique opportunity to constrain in a robust way the properties of the AMR. We present the AMR derived from analysing a pilot sample of 23 WDMS and provide clear evidence for the lack of correlation between age and metallicity at young and intermediate ages.

White dwarfs are natural cosmochronometers, and this allows us to use them to study relevant properties of the Galaxy, such as its age or its star formation rate history. Here we present a population synthesis study of the white dwarf population within 40 pc from the Sun, and compare the results of this study with the properties of the observed sample. We use a state-of-the-art population synthesis code based on Monte Carlo techniques that incorporates the most recent and reliable white dwarf cooling sequences, an accurate description of the Galactic neighborhood, and a realistic treatment of all the known observational biases.

We use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalog to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalog are available the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20,247 objects, making it the largest sample of white dwarfs with measured three-dimensional velocities. Furthermore, the volume probed by our sample is large, allowing us to obtain relevant kinematical information. In particular, our sample extends from a Galactocentric radial distance RG = 7.8 kpc to 9.3 kpc, and vertical distances from the Galactic plane ranging from Z = −0.5 kpc to 0.5 kpc. We examine the mean components of the stellar three-dimensional velocities, as well as their dispersions with respect to the Galactocentric and vertical distances. We confirm the existence of a mean Galactocentric radial velocity gradient, ∂〈VR〉/∂RG = −3 ± 5 km s−1 kpc−1. We also confirm North-South differences in 〈Vz〉. Specifically, we find that white dwarfs with Z > 0 (in the North Galactic hemisphere) have 〈Vz〉 < 0, while the reverse is true for white dwarfs with Z < 0. The age-velocity dispersion relation derived from the present sample indicates that the Galactic population of white dwarfs may have experienced an additional source of heating, which adds to the secular evolution of the Galactic disc.

We investigate the kinematics of stars in the Solar neighbourhood by combining radial velocities from the latest data release of the RAVE survey with the Tycho-Gaia Astrometric Solution presented in Gaia Data Release 1. We use moments of the velocity distribution to characterise the kinematics over a radial distance range of 6-10 kpc and up to 1 kpc away from the plane. Our ultimate goal is to use these to put new constraints on the (local) distribution of mass using the Jeans Equations.

Young associations, being sparsely populated and relatively close to the Sun, their members are found all over the sky. In the Solar Neighborhood, young moving groups are found within 100 pc with ages ranging from 5 to 120 Myr. While known members of these groups were identified mostly through the Hipparcos data, only the most massive members have been fully characterized so far, and defined the core members. In the last decades, several new candidate members have been identified, using different approaches. Based on the global properties of the core members (kinematics and over luminosity), those methods used several criteria to establish the membership, from qualitative manner to quantitive methods using reduced chi-squared or membership probability. A full confirmation of the membership for those numerous candidates requires radial velocity and parallax measurements to confirm their kinematics, age-dating indicator measurement to assess their youth and multiplicity follow-up to rule out binary objects. In this proceeding, we summarize a general recipe to assign membership, describe the numerous challenges for assigning membership, and end with a discussion on the appropriateness and reliability of the BANYAN I and II tools to assess membership.

Despite the recent advancements in the field of galaxy formation and evolution, fully self-consistent simulations are still unable to make the detailed predictions necessary for the planned and ongoing large spectroscopic and photometric surveys of the Milky Way disc. These difficulties arise from the very uncertain nature of sub-grid physical energy feedback within models, affecting both star formation rates and chemical enrichment. To avoid these problems, we have introduced a new approach which consists of fusing disc chemical evolution models with compatible numerical simulations. We demonstrate the power of this method by showing that a range of observational results can be explained by our new model. We show that due to radial migration from mergers at high redshift and the central bar at later times, a sizable fraction of old metal-poor, high-[α/Fe] stars can reach the solar vicinity. This naturally accounts for a number of recent observations related to both the thin and thick discs, despite the fact that we use thin-disc chemistry only. Within the framework of our model, the MW thick disc has emerged naturally from (i) stars born with high velocity dispersions at high redshift, (ii) stars migrating from the inner disc very early on due to strong merger activity, and (iii) further radial migration driven by the bar and spirals at later times. A significant fraction of old stars with thick-disc characteristics could have been born near the solar radius.

Resonances with spiral density waves or the Galactic bar can cause structure in local velocity distributions (also known as phase space). Because resonances are narrow, it is possible to place tight constraints on a pattern speed or the shape of the underlying gravitational potential.

Interference between multiple spiral patterns can cause localized bursts of star formation and discontinuities or kinks in the spiral arm morphology. Numerical simulations suggest that boundaries between different dominant patterns in the disk can manifest in local velocity distributions as gaps that are associated with specific orbital periods or angular momentum values. Recent studies have detected age gradients that may be associated with the appearance of spiral features such as armlets and spurs.

When patterns grow or vary in speed, resonances can be swept through the disk causing changes in the velocity distributions. Evidence of resonance capture or resonance crossing can be used to place constraints on the past history of patterns in the disk. The X-shaped Galactic bulge may have been caused by stars captured into vertical resonance with the Bar.

Disturbances in the Galactic disk, such as from a past merger, can cause an uneven distribution of disk stars in action angles. Subsequently the stellar distribution becomes more tightly wound in phase space. Phase wrapping can cause a series of shell like features in either real space or in a local velocity distribution. The spacing between features is dependent on the time since the disturbance.

Superjupiters are much brigther when they are young and still contracting, and the contrast with the harboring stars is significantly more favorable for their detection. Within the JOVIAN (Jupiter-like Objects in the Visible and the Infrared: Astrophysical Nature) project, a search has been performed for superjupiters around nearby young stars using 4 m class telescopes. Here we summarize the results and present prospects for a future search around young and also relatively older nearby stars with the 10 m Gran Telescopio Canarias and the mid-infrared camera CanariCam.