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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of Elliptical Galaxies and Other Spheroidal Components (1982)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 20 (1982), S. 399-429 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.20.090182.002151
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Warps (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 30 (1992), S. 51-74 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.30.090192.000411
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  • 3
    Electronic Resource
    Electronic Resource
    Unexpected stellar velocity distribution in the warped Galactic disk (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 392 (1998), S. 471-473 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It is now over 40 years since radio observations of neutral hydrogen revealed the gaseous disk of our Galaxy to be warped. Subsequently, the warp has been detected in the distribution of Galactic dust, molecular clouds, and luminous stars,. Roughly half of all spiral galaxies have similarly ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/33096
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  • 4
    Electronic Resource
    Electronic Resource
    Galaxies and magnetic fields (1993)
    [s.l.] : Nature Publishing Group
    Nature 365 (1993), S. 20-20 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Battaner et al.1 argue that the flat rotation curves of galaxies such as M31 may be caused not by dark matter, but by magnetic tension. In essence they suggest that the centripetal force required to hold together a rapidly spinning disk of gas is-provided by the tension of an azimuthal ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/365020a0
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  • 5
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    Bringing the Galaxy's dark halo to life (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-31
    Description: We present a new method to construct fully self-consistent equilibrium models of multicomponent disc galaxies similar to the Milky Way. We define distribution functions for the stellar disc and dark halo that depend on phase-space position only through action coordinates. We then use an iterative approach to find the corresponding gravitational potential. We study the adiabatic response of the initially spherical dark halo to the introduction of the baryonic component and find that the halo flattens in its inner regions with final minor–major axis ratios q  = 0.75–0.95. The extent of the flattening depends on the velocity structure of the halo particles with radially biased models exhibiting a stronger response. In this latter case, which is according to cosmological simulations the most likely one, the new density structure resembles a ‘dark disc’ superimposed on a spherical halo. We discuss the implications of these results for our recent estimate of the local dark matter (DM) density. The velocity distribution of the DM particles near the Sun is very non-Gaussian. All three principal velocity dispersions are boosted as the halo contracts, and at low velocities a plateau develops in the distribution of v z . For models similar to a state-of-the-art Galaxy model, we find velocity dispersions around 180 km s –1 for v z and the tangential velocity, v , and 150–205 km s –1 for the in-plane radial velocity, v R , depending on the anisotropy of the model.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Chemical separation of disc components using RAVE (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-29
    Description: We present evidence from the RAdial Velocity Experiment (RAVE) survey of chemically separated, kinematically distinct disc components in the solar neighbourhood. We apply probabilistic chemical selection criteria to separate our sample into α-low (‘thin disc’) and α-high (‘thick disc’) sequences. Using newly derived distances, which will be utilized in the upcoming RAVE DR5, we explore the kinematic trends as a function of metallicity for each of the disc components. For our α-low disc, we find a negative trend in the mean rotational velocity ( V ) as a function of iron abundance ([Fe/H]). We measure a positive gradient V /[Fe/H] for the α-high disc, consistent with results from high-resolution surveys. We also find differences between the α-low and α-high discs in all three components of velocity dispersion. We discuss the implications of an α-low, metal-rich population originating from the inner Galaxy, where the orbits of these stars have been significantly altered by radial mixing mechanisms in order to bring them into the solar neighbourhood. The probabilistic separation we propose can be extended to other data sets for which the accuracy in [α/Fe] is not sufficient to disentangle the chemical disc components a priori. For such data sets which will also have significant overlap with Gaia DR1, we can therefore make full use of the improved parallax and proper motion data as it becomes available to investigate kinematic trends in these chemical disc components.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The rich are different: evidence from the RAVE survey for stellar radial migration (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-26
    Description: Using the RAdial Velocity Experiment fourth data release (RAVE DR4), and a new metallicity calibration that will be also taken into account in the future RAVE DR5, we investigate the existence and the properties of supersolar metallicity stars ([ M /H]  +0.1 dex) in the sample, and in particular in the solar neighbourhood. We find that RAVE is rich in supersolar metallicity stars, and that the local metallicity distribution function declines remarkably slowly up to +0.4 dex. Our results show that the kinematics and height distributions of the supersolar metallicity stars are identical to those of the [ M /H]  0 thin-disc giants that we presume were locally manufactured. The eccentricities of the supersolar metallicity stars indicate that half of them are on a roughly circular orbit ( e  ≤ 0.15), so under the assumption that the metallicity of the interstellar medium at a given radius never decreases with time, they must have increased their angular momenta by scattering at corotation resonances of spiral arms from regions far inside the solar annulus. The likelihood that a star will migrate radially does not seem to decrease significantly with increasing amplitude of vertical oscillations within range of oscillation amplitudes encountered in the disc.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Gas flow in barred potentials (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-02
    Description: We use a Cartesian grid to simulate the flow of gas in a barred Galactic potential and investigate the effects of varying the sound speed in the gas and the resolution of the grid. For all sound speeds and resolutions, streamlines closely follow closed orbits at large and small radii. At intermediate radii shocks arise and the streamlines shift between two families of closed orbits. The point at which the shocks appear and the streamlines shift between orbit families depends strongly on sound speed and resolution. For sufficiently large values of these two parameters, the transfer happens at the cusped orbit as hypothesized by Binney et al. over two decades ago. For sufficiently high resolutions, the flow downstream of the shocks becomes unsteady. If this unsteadiness is physical, as appears to be the case, it provides a promising explanation for the asymmetry in the observed distribution of CO.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Extended distribution functions for our Galaxy (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-10
    Description: We extend models of our Galaxy based on distribution functions that are analytic functions of the action integrals to extended distribution functions (EDFs), which have an analytic dependence on metallicity as well. We use a simple, but physically motivated, functional forms for the metallicity of the interstellar medium as a function of radius and time and for the star formation rate, and a model for the diffusion of stars through phase space to suggest the required functional form of an EDF. We introduce a simple prescription for radial migration that preserves the overall profile of the disc while allowing individual stars to migrate throughout the disc. Our models explicitly consider the thin and thick discs as two distinct components separated in age. We show how an EDF can be used to incorporate realistic selection functions in models, and to construct mock catalogues of observed samples. We show that the selection function of the Geneva–Copenhagen Survey (GCS) biases in favour of young stars, which have atypically small random velocities. With the selection function taken into account our models produce good fits of the GCS data in chemo-dynamical space and the Gilmore & Reid ( 1983 ) density data. From our EDF, we predict the structure of the Sloan Extension for Galactic Understanding and Exploration G-dwarf sample. The kinematics are successfully predicted. The predicted metallicity distribution has too few stars with [Fe/H] ~= –0.5 dex and too many metal-rich stars. A significant problem may be the lack of any chemical–kinematic correlations in our thick disc. We argue that EDFs will prove essential tools for the analysis of both observational data and sophisticated models of Galaxy formation and evolution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Torus mapper: a code for dynamical models of galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-01
    Description: We present a freely downloadable software package for modelling the dynamics of galaxies, which we call the Torus Mapper ( tm ). The package is based around ‘torus mapping’, which is a non-perturbative technique for creating orbital tori for specified values of the action integrals. Given an orbital torus and a star's position at a reference time, one can compute its position at any other time, no matter how remote. One can also compute the velocities with which the star will pass through any given point and the contribution it will make to the time-averaged density there. A system of angle-action coordinates for the given potential can be created by foliating phase space with orbital tori. Such a foliation is facilitated by the ability of tm to create tori by interpolating on a grid of tori. We summarize the advantages of using tm rather than a standard time-stepper to create orbits, and give segments of code that illustrate applications of tm in several contexts, including setting up initial conditions for an N -body simulation. We examine the precision of the orbital tori created by tm and the behaviour of the code when orbits become trapped by a resonance.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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