37 research outputs found
Breaking beta: A comparison of mass modelling methods for spherical systems
We apply four different mass modelling methods to a suite of publicly
available mock data for spherical stellar systems. We focus on the recovery of
the density and velocity anisotropy as a function of radius, using either
line-of-sight velocity data only, or adding proper motion data. All methods
perform well on isotropic and tangentially anisotropic mock data, recovering
the density and velocity anisotropy within their 95% confidence intervals over
the radial range 0.25 < R/Rhalf < 4, where Rhalf is the half light radius.
However, radially-anisotropic mocks are more challenging. For line-of-sight
data alone, only methods that use information about the shape of the velocity
distribution function are able to break the degeneracy between the density
profile and the velocity anisotropy to obtain an unbiased estimate of both.
This shape information can be obtained through directly fitting a global phase
space distribution function, by using higher order 'Virial Shape Parameters',
or by assuming a Gaussian velocity distribution function locally, but
projecting it self-consistently along the line of sight. Including proper
motion data yields further improvements, and in this case, all methods give a
good recovery of both the radial density and velocity anisotropy profiles
Globular cluster systems and galaxy formation
Globular clusters are compact, gravitationally bound systems of up to a
million stars. The GCs in the Milky Way contain some of the oldest stars known,
and provide important clues to the early formation and continuing evolution of
our Galaxy. More generally, GCs are associated with galaxies of all types and
masses, from low-mass dwarf galaxies to the most massive early-type galaxies
which lie in the centres of massive galaxy clusters. GC systems show several
properties which connect tightly with properties of their host galaxies. For
example, the total mass of GCs in a system scales linearly with the dark matter
halo mass of its host galaxy. Numerical simulations are at the point of being
able to resolve globular cluster formation within a cosmological framework.
Therefore, GCs link a range of scales, from the physics of star formation in
turbulent gas clouds, to the large-scale properties of galaxies and their dark
matter. In this Chapter we review some of the basic observational approaches
for GC systems, some of their key observational properties, and describe how
GCs provide important clues to the formation of their parent galaxies.Comment: 32 pages, 6 figures. Accepted for publication in the book "Reviews in
Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds
Kabath, Jones and Skarka; publisher Springer Nature) funded by the European
Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
Amplitude analysis of the B0 (s)! K0K0 decays and measurement of the branching fraction of the B0! K0K0 decay
The and decays are studied using proton-proton collision data
corresponding to an integrated luminosity of 3fb. An untagged and
time-integrated amplitude analysis of
decays in two-body invariant mass regions of 150 MeV around the
mass is performed. A stronger longitudinal polarisation fraction in the decay, , is observed as compared to in the decay. The ratio of branching fractions of the two decays
is measured and used to determine .Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-004.html (LHCb
public pages
Heat pipes and solid sorption transformations: fundamentals and practical applications
Developing clean energy and utilizing waste energy has become increasingly vital. Research targeting the advancement of thermally powered adsorption cooling technologies has progressed in the past few decades, and the awareness of fuel cells and thermally activated (heat pipe heat exchangers) adsorption systems using natural refrigerants and/or alternatives to hydrofluorocarbon-based refrigerants is becoming ever more important. Heat Pipes and Solid Sorption Transformations: Fundamentals and Practical Applications concentrates on state-of-the-art adsorption research and technologies for relev