Abstract.Since the Hipparcos mission and recent large scale surveys in the optical and the near-infrared, new constraints have been obtained on the structure and evolution history of the Milky Way. The population synthesis approach is a useful tool to interpret such data sets and to test scenarios of evolution of the Galaxy. We present here new constraints on evolution parameters obtained from the Besançon model of population synthesis and analysis of optical and near-infrared star counts. The Galactic potential is computed self-consistently, in agreement with Hipparcos results and the observed rotation curve. Constraints are posed on the outer bulge structure, the warped and flared disc, the thick disc and the spheroid populations. The model is tuned to produce reliable predictions in the visible and the near-infrared in wide photometric bands from U to K. Finally, we describe applications such as photometric and astrometric simulations and a new classification tool based on a Bayesian probability estimator, which could be used in the framework of Virtual Observatories. As examples, samples of simulated star counts at different wavelengths and directions are also given.

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Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

We describe the Sloan

Aims. The Two Micron All Sky Survey, along with the Stellar Population Synthesis Model of the Galaxy, developed in Besançon, is used to calculate the extinction distribution along different lines of sight. By combining many lines of sight, the large scale distribution of interstellar material can be deduced.Methods. The Galaxy model is used to provide the intrinsic colour of stars and their probable distances, so that the near infrared colour excess, and hence the extinction, may be calculated and its distance evaluated. Such a technique is dependent on the model used, however we are able to show that moderate changes in the model parameters result in insignificant changes in the predicted extinction.Results. This technique has now been applied to over 64 000 lines of sight, each separated by 15 , in the inner Galaxy (|l| ≤ 100• , |b| ≤ 10• ). We have projected our three dimensional results onto a two dimensional plane in order to compare them with existing two dimensional extinction maps and CO surveys. We find that although differences exist due to the different methods used or the medium traced, the same large scale structures are visible in each of the different maps. Using our extinction map, we have derived the main characteristics of the large scale structure of the dust distribution. The scale height of the interstellar matter is found to be 125 +17 −7 pc. The dust distribution is found to be asymmetrically warped, in agreement with CO and HI observations of the ISM. However, the slope of the dust warp and the galactocentric distance where it starts are found to be smaller than the values measured for the external HI disc: for positive longitudes the angle is θ = 89• , it starts at 8.7 kpc from the Galactic center and grows with a slope of 0.14, while at negative longitudes, the angle of the maximum is at θ = 272• , the starting radius 7.8 kpc and the slope 0.11. Finally, the presence of dust is detected in the Galactic bulge. It forms an elongated structure approximately 5.2 kpc long and lies at an angle of 30 ± 5• with respect to the Sun-Galactic centre direction. This may be interpreted as a dust lane along the Galactic bar. This resulting extinction map will be useful for studies of the inner Galaxy and its stellar populations.

Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [α/Fe] vs. [Fe/H] plane and the metallicity distribution functions (MDF) across an unprecedented volume of the Milky Way disk, with radius 3 < R < 15 kpc and height |z| < 2 kpc. Stars in the inner disk (R < 5 kpc) lie along a single track in [α/Fe] vs. [Fe/H] , starting with α-enhanced, metal-poor stars and ending at [α/Fe] ∼ 0 and [Fe/H]∼ +0.4. At larger radii we find two distinct sequences in [α/Fe] vs. [Fe/H] space, with a roughly solar-α sequence that spans a decade in metallicity and a high-α sequence that merges with the low-α sequence at super-solar [Fe/H].The location of the high-α sequence is nearly constant across the disk, however there are very few high-α stars at R > 11 kpc. The peak of the midplane MDF shifts to lower metallicity at larger R, reflecting the Galactic metallicity gradient. Most strikingly, the shape of the midplane MDF changes systematically with radius, with a negatively skewed distribution at 3 < R < 7 kpc, to a roughly Gaussian distribution at the solar annulus, to a positively skewed shape in the outer Galaxy. For stars with |z| > 1 kpc or [α/Fe] > 0.18, the MDF shows little dependence on R. The positive skewness of the outer disk MDF may be a signature of radial migration; we show that blurring of stellar populations by orbital eccentricities is not enough to explain the reversal of MDF shape but a simple model of radial migration can do so.

The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z ∼ 0.52), 102,100 new quasar spectra (median z ∼ 2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T eff < 5000 K and in metallicity estimates for stars with [Fe/H] > −0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2).