3,026 research outputs found
The dynamical distance and intrinsic structure of the globular cluster omega Centauri
We determine the dynamical distance D, inclination i, mass-to-light ratio M/L
and the intrinsic orbital structure of the globular cluster omega Cen, by
fitting axisymmetric dynamical models to the ground-based proper motions of van
Leeuwen et al. and line-of-sight velocities from four independent data-sets. We
correct the observed velocities for perspective rotation caused by the space
motion of the cluster, and show that the residual solid-body rotation component
in the proper motions can be taken out without any modelling other than
assuming axisymmetry. This also provides a tight constraint on D tan i.
Application of our axisymmetric implementation of Schwarzschild's orbit
superposition method to omega Cen reveals no dynamical evidence for a
significant radial dependence of M/L. The best-fit dynamical model has a
stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an
inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic
axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3
kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained
by means of simple spherical or constant-anisotropy axisymmetric dynamical
models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by
photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6
M_sun. The best-fit model is close to isotropic inside a radius of about 10
arcmin and becomes increasingly tangentially anisotropic in the outer region,
which displays significant mean rotation. This phase-space structure may well
be caused by the effects of the tidal field of the Milky Way. The cluster
contains a separate disk-like component in the radial range between 1 and 3
arcmin, contributing about 4% to the total mass.Comment: 37 pages (23 figures), accepted for publication in A&A, abstract
abridged, for PS and PDF file with full resolution figures, see
http://www.strw.leidenuniv.nl/~vdven/oc
General solution of the Jeans equations for triaxial galaxies with separable potentials
The Jeans equations relate the second-order velocity moments to the density
and potential of a stellar system. For general three-dimensional stellar
systems, there are three equations and six independent moments. By assuming
that the potential is triaxial and of separable Staeckel form, the mixed
moments vanish in confocal ellipsoidal coordinates. Consequently, the three
Jeans equations and three remaining non-vanishing moments form a closed system
of three highly-symmetric coupled first-order partial differential equations in
three variables. These equations were first derived by Lynden-Bell, over 40
years ago, but have resisted solution by standard methods. We present the
general solution here.
We consider the two-dimensional limiting cases first. We solve their Jeans
equations by a new method which superposes singular solutions. The singular
solutions, which are new, are standard Riemann-Green functions. The
two-dimensional solutions are applied to non-axisymmetric discs, oblate and
prolate spheroids, and also to the scale-free triaxial limit. We then extend
the method of singular solutions to the triaxial case, and obtain a full
solution. The general solution can be expressed in terms of complete
(hyper)elliptic integrals which can be evaluated in a straightforward way, and
provides the full set of second moments which can support a triaxial density
distribution in a separable triaxial potential. (abridged)Comment: 28 pages (7 figures), LaTeX MN2e, accepted for publication in MNRA
The role of severity and intentionality in the intensity of Schadenfreude attribution:A developmental study of Danish children
Systemic lupus during pregnancy with refractory alveolar haemorrhage: recovery following termination of pregnancy
A case of refractory pulmonary hemorrhage in a pregnant 22-year-old with systemic lupus is presented. The clinical difficulty of management of pulmonary haemorrhage and lupus flare during pregnancy are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68549/2/10.1177_096120339700600909.pd
Formation of central massive objects via tidal compression
For a density that is not too sharply peaked towards the center, the local
tidal field becomes compressive in all three directions. Available gas can then
collapse and form a cluster of stars in the center, including or even being
dominated by a central black hole. We show that for a wide range of
(deprojected) Sersic profiles in a spherical potential, the tidal forces are
compressive within a region which encloses most of the corresponding light of
observed nuclear clusters in both late-type and early-type galaxies. In such
models, tidal forces become disruptive nearly everywhere for relatively large
Sersic indices n >= 3.5. We also show that the mass of a central massive object
(CMO) required to remove all radial compressive tidal forces scales linearly
with the mass of the host galaxy. If CMOs formed in (progenitor) galaxies with
n ~ 1, we predict a mass fraction of ~ 0.1-0.5%, consistent with observations
of nuclear clusters and super-massive black holes. While we find that tidal
compression possibly drives the formation of CMOs in galaxies, beyond the
central regions and on larger scales in clusters disruptive tidal forces might
contribute to prevent gas from cooling.Comment: 19 pages, 4 figures. Accepted for publication in ApJ. High resolution
version available at
http://www-obs.univ-lyon1.fr/labo/perso/eric.emsellem/preprint
22: Ex-vivo expansion (EvE) of previously cryopreserved cord blood (CB) into natural killer (NK) cells with enhanced AML and neuroblastoma cytotoxicity Potential role of CB NK cells in adoptive cellular immunotherapy (ACI)
Newsletter providing "a lighter, human interest side of the news" from the Boston University Medical Campus
Romedepsin (RM), A Hdaci, Significantly Increases The Expression Of NKG2D Ligands, MIC A/B, In Leukemia/Lymphoma Cells (LL), In Part Through The Glycogen Synthase Kinase-3 (GSK-3) Pathway, Resulting In Enhanced NK Cytotoxicity: Translational Approach For Adoptive NK Cell Immunotherapy
A study of rotating globular clusters - the case of the old, metal-poor globular cluster NGC 4372
Aims: We present the first in-depth study of the kinematic properties and
derive the structural parameters of NGC 4372 based on the fit of a Plummer
profile and a rotating, physical model. We explore the link between internal
rotation to different cluster properties and together with similar studies of
more GCs, we put these in the context of globular cluster formation and
evolution. Methods: We present radial velocities for 131 cluster member stars
measured from high-resolution FLAMES/GIRAFFE observations. Their membership to
the GC is additionally confirmed from precise metallicity estimates. Using this
kinematic data set we build a velocity dispersion profile and a systemic
rotation curve. Additionally, we obtain an elliptical number density profile of
NGC 4372 based on optical images using a MCMC fitting algorithm. From this we
derive the cluster's half-light radius and ellipticity as r_h=3.4'+/-0.04' and
e=0.08+/-0.01. Finally, we give a physical interpretation of the observed
morphological and kinematic properties of this GC by fitting an axisymmetric,
differentially rotating, dynamical model. Results: Our results show that NGC
4372 has an unusually high ratio of rotation amplitude to velocity dispersion
(1.2 vs. 4.5 km/s) for its metallicity. This, however, puts it in line with two
other exceptional, very metal-poor GCs - M 15 and NGC 4590. We also find a mild
flattening of NGC 4372 in the direction of its rotation. Given its old age,
this suggests that the flattening is indeed caused by the systemic rotation
rather than tidal interactions with the Galaxy. Additionally, we estimate the
dynamical mass of the GC M_dyn=2.0+/-0.5 x 10^5 M_Sun based on the dynamical
model, which constrains the mass-to-light ratio of NGC 4372 between 1.4 and 2.3
M_Sun/L_Sun, representative of an old, purely stellar population.Comment: Accepted for publication in A&A, 12 pages, 14 figures, 2 table
- …