12,671 research outputs found
Extending the Hyades
We explore the implications of models of the Hyades moving group in which it
has a resonant origin, for regions of the Galaxy beyond the Solar
neighbourhood. We show that while models associated with different resonances
can produce nearly identical substructure in the local velocity distribution,
the velocity distribution away from the Solar neighbourhood has different
properties for different models. In particular there is a variation between
different models of where in Galactocentric radius the observed Hyades signal
in velocity space is strongest, at a given Galactic azimuth. We note, however,
that the uncertainties in currently available data, primarily due to uncertain
distances to stars, hide these signatures rather effectively, meaning we are
not yet able to determine which resonance is the cause of the Hyades.Comment: 11 pages, 9 figures. MNRAS accepte
Making action-angle disc models for Gaia
A brief review of recent work. I describe dynamical modelling of the Milky
Way using action-angle coordinates. I explain what action-angle coordinates
are, and what progress has been made in the past few years to ensuring they can
be used in reasonably realistic Galactic potentials. I then describe recent
modelling efforts, and progress they have made in constraining the potential of
the Milky Way and the local dark matter density.Comment: 5 pages, published in the proceedings of the GREAT-ITN conference on
"The Milky Way Unravelled by Gaia", Barcelona, December 201
The uncertainty in Galactic parameters
We reanalyse the measurements of parallax, proper motion, and line-of-sight
velocity for 18 masers in high mass star-forming regions presented by Reid et
al. (2009). We use a likelihood analysis to investigate the distance of the Sun
from the Galactic centre, R_0, the rotational speed of the local standard of
rest, v_0, and the peculiar velocity of the Sun, vsol, for various models of
the rotation curve, and models which allow for a typical peculiar motion of the
high mass star-forming regions.
We find that these data are best fit by models with non-standard values for
vsol or a net peculiar motion of the high mass star-forming regions. We argue
that a correction to vsol is much more likely, and that these data support the
conclusion of Binney (2009) that V_sol should be revised upwards from 5.2 km/s
to 11 km/s. We find that the values of R_0 and v_0 that we determine are
heavily dependent on the model we use for the rotation curve, with
model-dependent estimates of R_0 ranging from 6.7 \pm 0.5kpc to 8.9 \pm 0.9kpc,
and those of v_0 ranging from 200 \pm 20 km/s to 279 \pm 33 km/s. We argue that
these data cannot be thought of as implying any particular values of R_0 or
v_0. However, we find that v_0/R_0 is better constrained, lying in the range
29.9-31.6 km/s/kpc for all models but one.Comment: 8 pages. MNRAS accepted. Revised to reflect final versio
Analysing surveys of our Galaxy I: basic astrometric data
We consider what is the best way to extract science from large surveys of the
Milky Way galaxy. The diversity of data gathered in these surveys, together
with our position within the Galaxy, imply that science must be extracted by
fitting dynamical models to the data in the space of the observables. Models
based on orbital tori promise to be superior for this task than traditional
types of models, such as N-body models and Schwarzschild models. A formalism
that allows such models to be fitted to data is developed and tested on
pseudodata of varying richness.Comment: 15 pages, 6 figures, MNRAS accepted, changed to reflect final versio
An implicit method for the calculation of inlet flow fields
Inlet flow fields are calculated by an implicit, time marching procedure to solve the thin layer Navier-Stokes equations formulated in body fitted coordinates. Because the method can be used for a flow field with both subsonic and supersonic regions, it is applicable to subcritical as well as supercritical inlet operation. Results are presented and discussed for an inlet of current design practice. Results include inviscid calculations performed for supercritical inlet operation with uniform and nonuniform inflow boundary conditions as well as for subcritical inlet operation with uniform inflow boundary conditions. Results for viscous calculations performed for supercritical inlet operation with uniform inflow boundary conditions are also discussed
Calculation of two-dimensional inlet flow fields by an implicit method including viscous effects: User's manual
Inlet flow fields for airbreathing missiles are calculated by the adaptation of a two dimensional computational method developed for the flow around airfoils. A supersonic free stream is assumed to allow the forebody calculation to be uncoupled from the inlet calculation. The inlet calculation employs an implicit, time marching finite difference procedure to solve the thin layer Navier-Stokes equations formulated in body fitted coordinates. The mathematical formulation of the problem and the solution algorithm are given. Numerical stability and accuracy as well as the initial and boundary conditions used are discussed. Instructions for program use and operation along with the overall program logic are also given
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