Chemically Peculiar (CP) stars have been the subject of systematic research for more than 50 years. With the discovery of pulsation of some of the cool CP stars, and the availability of advanced spectropolarimetric instrumentation and high signal-to-noise, high resolution spectroscopy, a new era of CP star research emerged about 20 years ago. Together with the success in ground-based observations, new space projects are developed that will greatly benefit future investigations of these unique objects. In this contribution we will give an overview of some interesting results obtained recently from ground-based observations and discuss the future outstanding Gaia space mission and its impact on CP star research.

The atmospheres of chemically peculiar stars can be highly structured in both the horizontal and vertical dimensions. While most prevalent in the magnetic stars, these structures can also exist in non-magnetic stars. In addition to providing an important window to understanding the physical processes at play in these complex atmospheres, they can also be exploited to study stellar pulsations. This article reviews contributions to the session “A 3D look into the atmosphere” of the Joint Discussion “Progress in understanding the physics of Ap and related stars”. It is divided into 3 sections: “Magnetic field and surface structures”, “Pulsations in the atmospheres of roAp stars/inversions”, and “Spectral synthesis/atmospheric models”.

We review the interaction in intermediate and high mass stars between their evolution and magnetic and chemical properties. We describe the theory of Ap-star ‘fossil’ fields, before touching on the expected secular diffusive processes which give rise to evolution of the field. We then present recent results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that magnetic fields of the kind seen on the main-sequence already exist during the pre-main sequence phase, in agreement with fossil field theory, and that the origin of the slow rotation of Ap/Bp stars also lies early in the pre-main sequence evolution; we also present results confirming a lack of stars with fields below a few hundred gauss. We then seek which macroscopic motions compete with atomic diffusion in determining the surface abundances of AmFm stars. While turbulent transport and mass loss, in competition with atomic diffusion, are both able to explain observed surface abundances, the interior abundance distribution is different enough to potentially lead to a test using asterosismology. Finally we review progress on the turbulence-driving and mixing processes in stellar radiative zones.

The body of photometric and astrometric data on stars in the Galaxy has been growing very fast in recent years (Hipparcos/Tycho, OGLE-3, 2-Mass, DENIS, UCAC2, SDSS, RAVE, Pan Starrs, Hermes, . . .) and in two years ESA will launch the Gaia satellite, which will measure astrometric data of unprecedented precision for a billion stars. On account of our position within the Galaxy and the complex observational biases that are built into most catalogues, dynamical models of the Galaxy are a prerequisite full exploitation of these catalogues. On account of the enormous detail in which we can observe the Galaxy, models of great sophistication are required. Moreover, in addition to models we require algorithms for observing them with the same errors and biases as occur in real observational programs, and statistical algorithms for determining the extent to which a model is compatible with a given body of data.

JD5 reviewed the status of our knowledge of the Galaxy, the different ways in which we could model the Galaxy, and what will be required to extract our science goals from the data that will be on hand when the Gaia Catalogue becomes available.

Gaia will perform an unprecedented high quality survey of the Milky Way. Distances, 3D kinematics, ages and abundances will be obtained, giving access to the overall mass distribution and to the Galactic potential. Gaia data analysis will involve a high level of complexity requiring new and efficient multivariate data analysis methods, improved modelling of the stellar populations and dynamical approaches to the interpretation of the data in terms of the chemical and dynamical evolution of the Galaxy.

The structure and dynamics of the Galaxy contain information about both its current workings and its assembly history. I review our understanding of the dynamics of the disk and stellar halo, and sketch how these may be used to unravel how our Galaxy formed.

Dynamical models have often necessarily assumed that the Galaxy is nearly steady state or dynamically relaxed. However observed structure in the stellar metallicity, spatial and velocity distributions imply that heating, mixing and radial migration has taken place. Better comprehension of non-equilibrium processes will allow us to not only better understand the current structure of the galaxy but its past evolution.

A selection of topics was discussed, but given the limits of space, I discuss here only the IMF in any depth, with only a brief supplementary comment on the bulge.

The Herschel and Planck satellites have started imaging the sky at far-IR to mm wavelengths with an unprecedented combination of sky and spectral coverage, angular resolution, and sensitivity, thus opening the last window of the electromagnetic spectrum on the Galaxy. Dedicated observing programs on Herschel and the Planck all-sky survey will provide the first complete view at cold dust across the Galaxy, opening new perspectives on the structure and dynamical evolution of the Milky Way relevant to Gaia. The analysis and modelling of these observations will contribute to our understanding of two key questions: how do stars form from interstellar matter? how are the interstellar medium and the magnetic field dynamically coupled? The comparison with Gaia observations will contribute to build a 3D model of the Galactic extinction taking into account dust evolution between ISM components

We discuss plans for a new joint effort between observers and theorists to understand the formation of the Milky Way halo back to the first epochs of chemical evolution. New models based on high-resolution N-body simulations coupled to simple models of Galactic chemical evolution show that surviving stars from the epoch of the first galaxies remain in the Milky Way today and should bear the nucleosynthetic imprint of the first stars. We investigate the key physical influences on the formation of stars in the first galaxies and how they appear today, including the relationship between cosmic reionization and surviving Milky Way stars. These models also provide a physically motivated picture of the formation of the Milky Ways “outer halo,” which has been identified from recent large samples of stars from SDSS. The next steps are to use these models to guide rigorous gas simulations of Milky Way formation, including its disk, and to gradually build up the fully detailed theoretical “Virtual Galaxy” that is demanded by the coming generation of massive Galactic stellar surveys.

The model of Schönrich & Binney (2009) offers new ways to understand the chemo-kinematic structure of the solar neighbourhood in the light of radial mixing. The combination of chemical information with rich kinematic data reveals a still hardly explored abundance of interconnections and structures from which we can learn about both the physics and history of our Galaxy. Large upcoming datasets can be used to improve estimates of central parameters, to shed light on the Galaxy's history and to explore the unexpected way of understanding the well-known division of the Galactic disc yielded by the new model.

In the recent years, more and more sophisticated models have been proposed for the gas distribution and kinematics in the Milky Way, taking into account the main bar, but also the possible nuclear bar, with the same or different pattern-speed. I review the success and problems encountered by the models, in particular in view of the new discovery of a symmetrical far-side counterpart of the 3 kpc arm. The inner part, dominated by the bar, and the outer parts, dominated by the spiral arms, can be observed from a virtual solar position, and the errors coming from kinematical distances are evaluated. The appearance of four arms could be due to a deprojection bias.

We summarize recent work on the Milky Way “tomography” with SDSS and use these results to illustrate what further breakthroughs can be expect from Gaia and the Large Synoptic Survey Telescope (LSST). LSST is the most ambitious ground-based survey currently planned in the visible band. Mapping of the Milky Way is one of the four main science and design drivers. The main 20 000 deg2. survey area will be imaged about 1000 times in six bands (ugrizy) during the anticipated 10 years of operations, with the first light expected in 2015. Due to Gaia's superb astrometric and photometric accuracy, and LSST's significantly deeper data, the two surveys are highly complementary: Gaia will map the Milky Way's disk with unprecedented detail, and LSST will extend this map all the way to the halo's edge.

Schwarzschild's orbit-superposition technique is the most developed and well-tested method available for constraining the detailed mass distributions of equilibrium stellar systems. Here I provide a very short overview of the method and its existing implementations, and briefly discuss their viability as a tool for modeling the Galaxy using Gaia data.

We use test-particle orbit integration with a realistic Milky Way (MW) potential to study the effect of the resonances of the Galactic bar and spiral arms on the velocity distribution of the Solar Neighbourhood and other positions of the disk. Our results show that spiral arms create abundant kinematic substructure and crowd stars into the region of the Hercules moving group in the velocity plane. Bar resonances can contribute to the origin of low-angular momentum moving groups like Arcturus. Particles in the predicted dark disk of the MW should be affected by the same resonances as stars, triggering dark-matter moving groups in the disk. Finally, we evaluate how this study will be advanced by upcoming Gaia data.

Recent simulations of forming low-mass galaxies suggests a strategy for obtaining realistic models of galaxies like the Milky-Way.

The principles and advantages of torus modelling are explained.

After a brief review of past N-body models of the Milky Way, I consider some of the difficulties that are inherent in the N-body approach to modelling any disk galaxy.

In this talk a brief introduction is given to made-to-measure particle methods and their potential use for modeling the Milky Way Galaxy.

We show that anomalous extinction (deviations from the traditionally adopted RV = AV/E(B − V) = 3.1 introduces large uncertainties in the distances of stars, for distances larger than 1-2 kpc. We argue that for such distances and for directions close to the galactic plane, the use of extinction models based on the gas distribution in the Galaxy is safer, for the moment, than the use of extinction maps.