Young objects (e.g. OB-associations and HII regions) in the Galaxy outline a 4-armed spiral structure whereas the tangent points of arms observed in the near-infrared indicate a 2-armed pattern. The more important issue is whether the spiral potential in the Galaxy is 2- or 4-armed i.e. if all arms traced by young objects also have a significant mass perturbation associated to them. This can be tested by studying the mean radial velocity of a well defined stellar population across the spiral arms and thereby estimating the surface density change.

The current paper presents a preliminary analysis of the radial velocities of a sample of 736 early-type stars toward the Galactic center observed with FLAMES/VLT. A comparison with N-body models in a fixed spiral potential with 2 or 4 arms suggests that no significant mass is associated to the Sagittarius arm. The data are consistent with 2-armed models with pattern speeds in the range of 15-30 km s−1 kpc−1 and relative radial forces of less than 4%.

In the context of the Radial Velocity Experiment (RAVE, Steinmetz et al. 2006), we present chemical abundances derived with the pipeline GAUGUIN. Based of 520 701 RAVE stars with medium resolution (R~7 500) spectra and stellar atmospheric parameters of the fifth Data Release, the analysis is performed around the infrared Ca-triple domain for 6 chemical elements: Mg, Ni, Si, Ti, Fe and Al. We discuss here the reliability of the chemical abundances provided by GAUGUIN, and the implications for the future Data Release 6 of the RAVE Survey. We also present elemental abundance patterns of Milky Way components based of kinematical criteria.

We investigate the kinematics of red clump stars in the Solar neighbourhood by combining data from the RAVE survey with the TGAS dataset presented in Gaia DR1. Our goal is to put new constraints on the (local) distribution of mass using the Jeans Equations. Here we show the variation of the vertical velocity dispersion as function of height above the mid-plane for both a thin and a thick disk tracer sample and present preliminary results.

We present the derived kinematic characteristics of low-α thin-disk and high-α thick-disk stars in the Milky Way, investigated with a sample of about 32,000 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of α-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocities, velocity dispersions, and velocity gradients for the U, V, and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: −23 km s−1 dex−1 for the thin disk and +44 km s−1 dex−1 for the thick disk. The velocity dispersion of the thick disk decreases with increasing [Fe/H], while the velocity dispersion gradient over [Fe/H] for the thin disk is almost flat for all velocity components, except for the W velocity dispersion of the metal-poor thin-disk stars. The eccentricity distribution exhibits a peak at a higher value, and is more symmetric as [α/Fe] increases, implying that complex formation mechanisms may be involved. Our results can be used to constrain several proposed disk-formation scenarios of the Milky Way and other large spirals.

Phylogenetics is a widely used concept in evolutionary biology. It is the reconstruction of evolutionary history by building trees that represent branching patterns and sequences. These trees represent shared history, and it is our contention that this approach can be employed in the analysis of Galactic history. In Galactic archaeology the shared environment is the interstellar medium in which stars form and provides the basis for tree-building as a methodological tool. Using elemental abundances of solar-type stars as a proxy for DNA, we built such an evolutionary tree to study the chemical evolution of the solar neighbourhood and published in Jofré15 et al. (2017). In this proceeding we summarise these results and discuss future prospects.

We used our detailed analytic local disc model to compare predictions in number counts, colour distribuitons and kinematics with a data set extracted from a combination of TGAS and RAVE catalogues. We find generally a very good agreement with some deviations close to the Galactic plane.

Open clusters are important objects to study the galactic structure and its dynamical behavior as well as the stellar formation and evolution. We carried out a spectroscopic analysis to derive atmospheric parameters and chemical composition for 52 giant stars within 9 galactic open clusters. We have used the high-resolution spectra from FEROS, HARPS and UVES in the ESO archive. The methodology used is based on LTE-hypothesis. Abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Ni, YII, LaII, CeII, and NdII were calculated. Although most of these clusters present spectroscopic analysis in the literature, some CNO and s-process abundances were not previously estimated or were calculated with high uncertainties. Several lines of such elements were identified and used to calculate new abundances and improve some previous one.

To explore the relation between bar formation and star formation in Milky Way-type galaxies quantitatively, we simulated gas-rich disk isolated galaxies. We find that the action of the stellar bar efficiently quenches star formation, reducing the star-formation rate by a factor of 10 in less than 1 Gyr. Analytical and self-consistent galaxy simulations with bars suggest that the action of the stellar bar increases the gas random motions within the co-rotation radius of the bar. Indeed, we detect an increase in the gas velocity dispersion at the end of the bar formation phase. The star formation efficiency decreases rapidly, and in all of our models, the bar quenches the star formation in the galaxy. The star-formation efficiency is much lower in simulated barred compared to unbarred galaxies and more rapid bar formation implies more rapid quenching.

In order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters (GCs). Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars (WMS), together with the winds and ejecta from low and intermediate mass asymptotic-giant-branch stars (AGBs), are all locally retained in these less massive systems. We find that the observed Na-O anti-correlations in metal-poor GCs can be reproduced, when multiple episodes of starbursts are allowed to continue in these subsystems. A specific form of star formation history (SFH) with decreasing time intervals between the stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from our stellar evolution models for the horizontal-branch. The “mass budget problem” is also much alleviated by our models without ad-hoc assumptions on star formation efficiency (SFE) and initial mass function (IMF). We also applied these models to investigate the origin of super-helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the WMS can naturally reproduce the required helium enhancement (ΔY/ΔZ = 6) for the second generation stars. Disruption of proto-GCs in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field.

We have carried out an imaging survey for Local Group dwarf spheroidal galaxy Ursa Minor (UMi) using Hyper Suprime-Cam (HSC) on the 8.2m Subaru Telescope. Wide and deep data obtained by HSC enable us to investigate the extent of UMi which is revealed to extend out to twice the nominal tidal radius. The fraction of binary systems is also investigated from the morphology of the main sequence and estimated to be ~0.4.

We present here a model that allows us to predict the properties of gaps in stellar streams, and how these depend on the parameters of the encounters (satellite mass, size and relative velocity). Since the gaps we consider are created by dark matter satellites we hope to use our understanding to constrain the properties of dark matter.

With the much enlarged stellar sample of 55 831 stars and much increased precision in distances, proper motions, provided by Gaia DR1 TGAS we have shown with the help of the wavelet analysis that the velocity distribution of stars in the Solar neighbourhood contains more kinematic structures than previously known. We detect 19 kinematic structures between scales 3-16 km s−1 at the 3σ confidence level. Among them we identified well-known groups (such as Hercules, Sirius, Coma Berenices, Pleiades, and Wolf 630). We confirmed recently detected groups (such as Antoja12 and Bobylev16). In addition we report here about a new kinematic structure at (U, V) ≈ (37, 8) km s−1. Another three new groups are tentatively detected, but require confirmation.

The cornerstone mission of the European Space Agency, Gaia, together with forthcoming complementary surveys (CoRoT, Kepler, K2, APOGEE and Gaia-ESO), will revolutionize our understanding of the formation and history of our Galaxy, providing accurate stellar masses, radii, ages, distances, as well as chemical properties for a very large sample of stars across different Galactic stellar populations. Using improved population synthesis approach and new stellar evolution models we attempt to evaluate the possibility to derive ages of clump stars from their chemical properties. A new version of the Besançon Galaxy models (BGM) is used in which new stellar evolutionary tracks are computed from the stellar evolution code STAREVOL. The effects of mixing on chemical composition of the stellar photosphere has a significant impact on the determined stellar age from the observed [C/N] ratio. We clearly show that transport processes occurring in red-giant stars should be taken into account in the determination of ages for future Galactic archaeology studies.

There is growing evidence that, among the various subclasses of carbon-enhanced metal-poor (CEMP) stars, the outer halo of the Milky Way exhibits a higher frequency of CEMP-no stars (those having no over-abundances of heavy neutron-capture elements) compared with the CEMP-s stars (those with over-enhancements of the s-process elements), while the inner halo shows a higher frequency of CEMP-s stars. We map out fractions of CEMP-no and CEMP-s stars in the inner- and outer-halo populations, separated by their spatial distribution of carbonicity ([C/Fe]), a so-called “carbonicity map”, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. The CEMP-no and CEMP-s objects are classified by different levels of absolute carbon abundances for our sample, A(C). We also present kinematic and orbital characteristics of these subclasses for each population. The contrast appearing in these characteristics provides critical constraints on the assembly history of the two primary stellar components of the Galactic halo.

Cepheids are excellent stellar tracers: they are bright enough to be observed even at large distances; their distances can be accurately determined via period-luminosity relations; their spectra contain numerous lines that enable us to derive abundances for many α, iron-peak or neutron-capture elements. Classical Cepheids are yellow supergiants that trace the young populations (⩽ 300 Myr); Type II Cepheids are post Horizontal Branch, low-mass, Population II stars (⩾ 10 Gyr). Both can be used for many purposes in Milky Way archaeology.

The fundamental plane (FP) is the relation between the surface brightness (I), velocity dispersion (σ) and radius (R). The tilt of FP from the virial plane (R = σ2I) not only tells the dynamical states of the system but also its formation and evolution. We motivate to looking for an FP in Galactic open clusters (OCs). To form a sample of OCs, we access the most recent DR 14 data from the SDSS/APOGEE2 and the Gaia-ESO survey. Membership of stars is determined via radial velocity and metallicity, plus star’s location in the color-magnitude diagram. Besides the velocity dispersion (σrv) obtained from SDSS/APOGEE2 & Gaia-ESO, the average surface brightness (IKs), and apparent radii (r2) of OCs are taken from known OC catalog. A weak relation is found: log(r2) ∝ -0.34 * log(σ) - 0.08 * IKs. An implication of this FP needs further investigation.

Based on high-resolution spectral observations for a sample of very metal-poor stars, we investigate how well stellar chemical abundances can be derived with available theoretical methods and computational tools.

We have conducted a large-scale survey of variable stars in the northern Galactic plane, about 320 square degrees using Kiso Wide Field Camera attached to the 105-cm Schmidt telescope at Kiso observatory. In the KISOGP (KWFC Intensive Survey of the Galactic Plane), we collected 40–100 epoch I-band images between 2012 and 2017. In our survey region roughly 5 million stars exist down to the limiting magnitude of ~16.5 mag in I. In the initial data analysis, we detected a couple of thousands of variable stars including approximately 100 Cepheids and more than 700 Miras. More than 80 percents of them were not previously reported as variable stars, indicating that there are still many relatively bright variables to be found in the Galactic plane.

We report the results of abundance analysis for high-resolution spectra of eight extremely metal-poor turn-off stars selected from SDSS/SEGUE. Based on differential analysis adopting stellar parameters from Balmer line profiles, we obtain the following results: i) Statistically significant scatter is found in [X/Fe] (X=Na, Mg, Cr, Ti, Sr and Ba), among which [Na/Fe] shows an apparent bimodal distribution, ii) Li abundances are ~0.3 dex lower in [Fe/H]<−3.5 than the Spite plateau value without significant scatter.