Publications by James Binney

Dynamical models and Galaxy surveys

Proceedings of the International Astronomical Union Cambridge University Press (CUP) 9 (2013) 117-129

J Binney, JL Sanders

<jats:title>Abstract</jats:title><jats:p>Equilibrium dynamical models are essential tools for extracting science from surveys of our Galaxy. We show how models can be tested with data from a survey before the survey's selection function has been determined. We illustrate the application of this method by presenting some results for the RAVE survey. We extend our published analytic distribution functions to include chemistry and fit the chosen functional form to a combination of the Geneva–Copenhagen survey (GCS) and a sample of G-dwarfs observed at<jats:italic>z</jats:italic>~ 1.75 kpc by the SEGUE survey. By including solid dynamics we are able to predict the contribution that the thick disc/halo stars surveyed by SEGUE should make to the GCS survey. We show that the measured [Fe/H] distribution from the GCS includes many fewer stars at [Fe/H] &lt; −0.6 than are predicted. The problem is more likely to lie in discordant abundance scales than with incorrect dynamics.</jats:p>

Dynamics for galactic archaeology

New Astronomy Reviews (2013)

J Binney

Our Galaxy is a complex machine in which several processes operate simultaneously: metal-poor gas is accreted, is chemically enriched by dying stars, and then drifts inwards, surrendering its angular momentum to stars; new stars are formed on nearly circular orbits in the equatorial plane and then diffuse through orbit space to eccentric and inclined orbits; the central stellar bar surrenders angular momentum to the surrounding disc and dark halo while acquiring angular momentum from inspiralling gas; the outer parts of the disc are constantly disturbed by satellite objects, both luminous and dark, as they sweep through pericentre. We review the conceptual tools required to bring these complex happenings into focus. Our first concern must be the construction of equilibrium models of the Galaxy, for upon these hang our hopes of determining the Galaxy's mean gravitational field, which is required for every subsequent step. Ideally our equilibrium model should be formulated so that the secular evolution of the system can be modelled with perturbation theory. Such theory can be used to understand how stars diffuse through orbit space from either the thin gas disc in which we presume disc stars formed, or the debris of an accreted object, the presumed origin of many halo stars. Coupling this understanding to the still very uncertain predictions of the theory of stellar evolution and nucleosynthesis, we can finally extract a complete model of the chemodynamic evolution of our reasonably generic Galaxy. We discuss the relation of such a model to cosmological simulations of galaxy formation, which provide general guidance but cannot be relied on for quantitative detail. © 2013.

Stream–orbit misalignment – II. A new algorithm to constrain the Galactic potential

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 433 (2013) 1826-1836

JL Sanders, J Binney

Stream–orbit misalignment – I. The dangers of orbit-fitting

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 433 (2013) 1813-1825

JL Sanders, J Binney

Analysing surveys of our Galaxy - II. Determining the potential


PJ McMillan, JJ Binney



F Fraternali, A Marasco, F Marinacci, J Binney

Actions for axisymmetric potentials

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 426 (2012) 1324-1327

J Binney

More dynamical models of our Galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 426 (2012) 1328-1337

J Binney

The properties of the local spiral arms from RAVE data: two-dimensional density wave approach


A Siebert, B Famaey, J Binney, B Burnett, C Faure, I Minchev, MEK Williams, O Bienayme, J Bland-Hawthorn, C Boeche, BK Gibson, EK Grebel, A Helmi, A Just, U Munari, JF Navarro, QA Parker, WA Reid, G Seabroke, A Siviero, M Steinmetz, T Zwitter

The detection and treatment of distance errors in kinematic analyses of stars

Monthly Notices of the Royal Astronomical Society 420 (2012) 1281-1293

R Schönrich, J Binney, M Asplund

We present a new method for detecting and correcting systematic errors in the distances to stars when both proper motions and line-of-sight velocities are available. The method, which is applicable for samples of 200 or more stars that have a significant extension on the sky, exploits correlations between the measured U, V and W velocity components that are introduced by distance errors. We deliver a formalism to describe and interpret the specific imprints of distance errors including spurious velocity correlations and shifts of mean motion in a sample. We take into account correlations introduced by measurement errors, Galactic rotation and changes in the orientation of the velocity ellipsoid with position in the Galaxy. Tests on pseudo-data show that the method is more robust and sensitive than traditional approaches to this problem. We investigate approaches to characterizing the probability distribution of distance errors, in addition to the mean distance error, which is the main theme of the paper. Stars with the most overestimated distances bias our estimate of the overall distance scale, leading to the corrected distances being slightly too small. We give a formula that can be used to correct for this effect. We apply the method to samples of stars from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, exploring optimal gravity cuts, sample contamination, and correcting the used distance relations. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Analysing surveys of our Galaxy - I. Basic astrometric data


PJ McMillan, J Binney

Supernova-driven gas accretion in the Milky Way


A Marasco, F Fraternali, JJ Binney

A new formula for disc kinematics

Monthly Notices of the Royal Astronomical Society 419 (2012) 1546-1556

R Schönrich, J Binney

In a disc galaxy, the distribution of azimuthal components of velocity is very skew. In the past, this skewness has been modelled by superposed Gaussians. We use dynamical arguments to derive an analytic formula that can be fitted to observed velocity distributions, and validate it by fits to the velocities derived from a dynamically rigorous model, and to a sample of local stars with accurate space velocities. Our formula is much easier to use than a full distribution function. It has fewer parameters than a multi-Gaussian fit, and the best-fitting model parameters give insight into the underlying disc dynamics. In particular, once the azimuthal velocities of a sample have been successfully fitted, the apparatus provides a prediction for the corresponding distribution of radial velocitiesvR. An effective formula like ours is invaluable when fitting to data for stars at some distance from the Sun because it enables one to make proper allowance for the errors in distance and proper motion when determining the underlying disc kinematics. The derivation of our formula elucidates the way the horizontal and vertical motions are closely intertwined, and makes it evident that no stellar population can have a scaleheight and vertical velocity dispersions that are simultaneously independent of radius. We show that the oscillation of a star perpendicular to the Galactic plane modifies the effective potential in which the star moves radially in such a way that the more vertical energy a star has, the larger is the mean radius of its orbit. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Fountain-driven gas accretion by the Milky Way


F Marinacci, F Fraternali, J Binney, C Nipoti, L Ciotti, P Londrillo

Comparing theoretical models of our galaxy with observations


S Sharma, J Bland-Hawthorn, KV Johnston, J Binney

Accretion by the Galaxy

EPJ Web of Conferences EDP Sciences 19 (2012) 08001-08001

J Binney, F Fraternali

Galactic fountains and the rotation of disc-galaxy coronae

Monthly Notices of the Royal Astronomical Society 415 (2011) 1534-1542

F Marinacci, F Fraternali, C Nipoti, J Binney, L Ciotti, P Londrillo

In galaxies like the Milky Way, cold (~104K) gas ejected from the disc by stellar activity (the so-called galactic-fountain gas) is expected to interact with the virial-temperature (~106K) gas of the corona. The associated transfer of momentum between cold and hot gas has important consequences for the dynamics of both gas phases. We quantify the effects of such an interaction using hydrodynamical simulations of cold clouds travelling through a hot medium at different relative velocities. Our main finding is that there is a velocity threshold between clouds and corona, of about 75kms-1, below which the hot gas ceases to absorb momentum from the cold clouds. It follows that in a disc galaxy like the Milky Way a static corona would be rapidly accelerated; the corona is expected to rotate and to lag, in the inner regions, by ~80-120kms-1 with respect to the cold disc. We also show how the existence of this velocity threshold can explain the observed kinematics of the cold extraplanar gas. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Distance determination for RAVE stars using stellar models III. The nature of the RAVE survey and Milky Way chemistry


B Burnett, J Binney, S Sharma, M Williams, T Zwitter, O Bienayme, J Bland-Hawthorn, KC Freeman, J Fulbright, B Gibson, G Gilmore, EK Grebel, A Helmi, U Munari, JF Navarro, QA Parker, GM Seabroke, A Siebert, A Siviero, M Steinmetz, FG Watson, RFG Wyse

Extracting science from surveys of our Galaxy

Pramana - Journal of Physics 77 (2011) 39-52

J Binney

Our knowledge of the Galaxy is being revolutionized by a series of photometric, spectroscopic and astrometric surveys. Already an enormous body of data is available from completed surveys, and data of ever-increasing quality and richness will accrue at least until the end of this decade. To extract science from these surveys, we need a class of models that can give probability density functions in the space of the observables of a survey - we should not attempt to 'invert' the data from the space of observables into the physical space of the Galaxy. Currently just one class of model has the required capability, the so-called 'torus models'. A pilot application of torus models to understand the structure of the Galaxy's thin and thick discs has already produced two significant results: a major revision of our best estimate of the Sun's velocity with respect to the local standard of rest, and a successful prediction of the way in which the vertical velocity dispersion in the disc varies with distance from the Galactic plane. © Indian Academy of Sciences.

The radial velocity experiment (RAVE): Third data release

Astronomical Journal 141 (2011)

A Siebert, MEK Williams, A Siviero, W Reid, C Boeche, M Steinmetz, J Fulbright, U Munari, T Zwitter, FG Watson, RFG Wyse, RS De Jong, H Enke, B Anguiano, D Burton, CJP Cass, K Fiegert, M Hartley, A Ritter, KS Russel, M Stupar, O Bienaymé, KC Freeman, G Gilmore, EK Grebel, A Helmi, JF Navarro, J Binney, J Bland-Hawthorn, R Campbell, B Famaey, O Gerhard, BK Gibson, G Matijevič, QA Parker, GM Seabroke, S Sharma, MC Smith, E Wylie-De Boer

We present the third data release of the RAdial Velocity Experiment (RAVE) which is the first milestone of the RAVE project, releasing the full pilot survey. The catalog contains 83,072 radial velocity measurements for 77,461 stars in the southern celestial hemisphere, as well as stellar parameters for 39,833 stars. This paper describes the content of the new release, the new processing pipeline, as well as an updated calibration for the metallicity based upon the observation of additional standard stars. Spectra will be made available in a future release. The data release can be accessed via the RAVE Web site. © 2011. The American Astronomical Society. All rights reserved.