371 research outputs found
Red giants in the outer halo of the elliptical galaxy NGC 5128 / Centaurus A
We used VIMOS on VLT to perform and band imaging of the outermost
halo of NGC 5128 / Centaurus A (), 65 kpc from the
galaxy's center and along the major axis. The stellar population has been
resolved to with a completeness limit of ,
well below the tip of the red-giant branch (TRGB), which is seen at . The surface density of NGC 5128 halo stars in our fields was
sufficiently low that dim, unresolved background galaxies were a major
contaminant in the source counts. We isolated a clean sample of
red-giant-branch (RGB) stars extending to mag below the TRGB
through conservative magnitude and color cuts, to remove the (predominantly
blue) unresolved background galaxies. We derived stellar metallicities from
colors of the stars via isochrones and measured the density falloff of the halo
as a function of metallicity by combining our observations with HST imaging
taken of NGC 5128 halo fields closer to the galaxy center. We found both
metal-rich and metal-poor stellar populations and found that the falloff of the
two follows the same de Vaucouleurs' law profiles from kpc out to
70 kpc. The metallicity distribution function (MDF) and the density
falloff agree with the results of two recent studies of similar outermost halo
fields in NGC 5128. We found no evidence of a "transition" in the radial
profile of the halo, in which the metal-rich halo density would drop rapidly,
leaving the underlying metal-poor halo to dominate by default out to greater
radial extent, as has been seen in the outer halo of two other large galaxies.
If NGC 5128 has such a transition, it must lie at larger galactocentric
distances.Comment: Accepted for publication in A&A. 11 pages, including 14 figures and 1
tabl
Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and
The anisotropy parameter characterizes the extent to which orbits in
stellar systems are predominantly radial or tangential, and is likely to
constrain, for the stellar halo of the Milky Way, scenarios for its formation
and evolution. We have measured the anisotropy as a function of
Galactocentric radius from kpc for over 8600 metal poor ([Fe/H]
) halo K giants from the LAMOST catalog with line-of-sight velocities
and distances, matched to proper motions from the second data release.
We construct full 6-D positions and velocities for the K giants to directly
measure the 3 components of the velocity dispersion (in spherical coordinates). We find that the orbits in the halo
are radial over our full Galactocentric distance range reaching over 100 kpc.
The anisotropy remains remarkably unchanged with Galactocentric radius from
approximately 5 to 25 kpc, with an amplitude that depends on the metallicity of
the stars, dropping from for [Fe/H]
(for the bulk of the stars) to for the lowest metallicities
([Fe/H] ). Considering our sample as a whole, and,
beyond 25 kpc, the orbits gradually become less radial and anisotropy decreases
to past 100 kpc. Within 8 kpc, . The measurement of
anisotropy is affected by substructure and streams, particularly beyond a
Galactocentric distance of approximately 25 kpc, where the Sagittarius stream
is prominent in the data. These results are complimentary to recent analysis of
simulations by Loebman et al. and of SDSS/ DR1 data by Belokurov et al.Comment: 9 pages, 5 figures, published versio
Exploring asymmetric substructures of the outer disk based on the conjugate angle of the radial action
We use the conjugate angle of radial action (), the best
representation of the orbital phase, to explore the "mid-plane, north branch,
south branch" and "Monoceros area" disk structures that were previously
revealed in the LAMOST K giants (Xu et al. 2020). The former three
substructures, identified by their 3D kinematical distributions, have been
shown to be projections of the phase space spiral (resulting from
nonequilibrium phase mixing). In this work, we find that all of these
substructures associated with the phase spiral show high aggregation in
conjugate angle phase space, indicating that the clumping in conjugate angle
space is a feature of ongoing, incomplete phase mixing. We do not find the
phase spiral located in the "Monoceros area", but we do find a very
highly concentrated substructure in the quadrant of conjugate angle space with
the orbital phase from the apocenter to the guiding radius. The existence of
the clump in conjugate angle space provides a complementary way to connect the
"Monoceros area" with the direct response to a perturbation from a significant
gravitationally interactive event. Using test particle simulations, we show
that these features are analogous to disturbances caused by the impact of the
last passage of the Sagittarius dwarf spheroidal galaxy.Comment: 53pages, 35 figures, 4 Tables, ApJ accepte
Five More Massive Binaries in the Cygnus OB2 Association
We present the orbital solutions for four OB spectroscopic binaries, MT145,
GSC 03161-00815, 2MASS J20294666+4105083, and Schulte 73, and the partial
orbital solution to the B spectroscopic binary, MT372, as part of an ongoing
study to determine the distribution of orbital parameters for massive binaries
in the Cygnus OB2 Association. MT145 is a new, single-lined, moderately
eccentric (e=0.291+/-0.009) spectroscopic binary with period of 25.140+/-0.008
days. GSC 03161-00815 is a slightly eccentric (e=0.10+/-0.01), eclipsing,
interacting and double-lined spectroscopic binary with a period of
4.674+/-0.004 days. 2MASS J20294666+4105083 is a moderately eccentric
(e=0.273+/-0.002) double-lined spectroscopic binary with a period of
2.884+/-0.001 days. Schulte 73 is a slightly eccentric (e=0.169+/-0.009),
double-lined spectroscopic binary with a period of 17.28+/-0.03 days and the
first "twin" in our survey with a mass ratio of q=0.99+/-0.02. MT372 is a
single-lined, eclipsing system with a period of 2.228 days and low eccentricity
(e~0). Of the now 18 known OB binaries in Cyg OB2, 14 have periods and mass
ratios. Emerging evidence also shows that the distribution of log(P) is flat
and consistent with Oepik's Law.Comment: Accepted to Astronomical Journa
Numerical Methods for the Stochastic Landau-Lifshitz Navier-Stokes Equations
The Landau-Lifshitz Navier-Stokes (LLNS) equations incorporate thermal
fluctuations into macroscopic hydrodynamics by using stochastic fluxes. This
paper examines explicit Eulerian discretizations of the full LLNS equations.
Several CFD approaches are considered (including MacCormack's two-step
Lax-Wendroff scheme and the Piecewise Parabolic Method) and are found to give
good results (about 10% error) for the variances of momentum and energy
fluctuations. However, neither of these schemes accurately reproduces the
density fluctuations. We introduce a conservative centered scheme with a
third-order Runge-Kutta temporal integrator that does accurately produce
density fluctuations. A variety of numerical tests, including the random walk
of a standing shock wave, are considered and results from the stochastic LLNS
PDE solver are compared with theory, when available, and with molecular
simulations using a Direct Simulation Monte Carlo (DSMC) algorithm
Modelling hepatitis C infection acquired from blood transfusions in the UK between 1970 and 1991 for the Infected Blood Inquiry
The Statistics Expert Group was convened at the request of the Infected Blood Inquiry to provide estimates of the number of infections and deaths from blood-borne infections including hepatitis B virus, human immunodeficiency virus, hepatitis C virus (HCV) and variant Creutzfeldt Jakob disease, as a direct result of contaminated blood and blood products administered in the United Kingdom of Great Britain and Northern Ireland (UK). In the absence of databases of HCV infections and related deaths for all nations of the UK, a statistical model was required to estimate the number of infections and subsequent deaths from HCV acquired from blood transfusions from January 1970 to August 1991. We present this statistical model in detail alongside the results of its application to each of the four nations in the UK. We estimated that 26 800 people (95% uncertainty interval 21 300–38 800) throughout the UK were chronically infected with HCV because of contaminated blood transfusions between January 1970 and August 1991. The number of deaths up to the end of 2019 that occurred as a result of this chronic infection is estimated to be 1820 (95% uncertainty interval 650–3320)
Neural processing associated with cognitive and affective Theory of Mind in adolescents and adults
Theory of Mind (ToM) is the ability to attribute thoughts, intentions and beliefs to others. This involves component processes, including cognitive perspective taking (cognitive ToM) and understanding emotions (affective ToM). This study assessed the distinction and overlap of neural processes involved in these respective components, and also investigated their development between adolescence and adulthood. While data suggest that ToM develops between adolescence and adulthood, these populations have not been compared on cognitive and affective ToM domains. Using fMRI with 15 adolescent (aged 11–16 years) and 15 adult (aged 24–40 years) males, we assessed neural responses during cartoon vignettes requiring cognitive ToM, affective ToM or physical causality comprehension (control). An additional aim was to explore relationships between fMRI data and self-reported empathy. Both cognitive and affective ToM conditions were associated with neural responses in the classic ToM network across both groups, although only affective ToM recruited medial/ventromedial PFC (mPFC/vmPFC). Adolescents add- itionally activated vmPFC more than did adults during affective ToM. The specificity of the mPFC/vmPFC response during affective ToM supports evidence from lesion studies suggesting that vmPFC may integrate affective information during ToM. Furthermore, the differential neural response in vmPFC between adult and adolescent groups indicates developmental changes in affective ToM processing
Witness: The Modern Writer as Witness
Editor\u27s Note [Excerpt] The United States, as a society, is on the brink of profound and positive change. Demographically and culturally, things are improving, and the reason is obvious to people who study history: Conflict pushes us to be better, to strive for principled goals. Consider the inspired eco-advocacy of Greta Thunberg. Or the swearing in of most diverse class of lawmakers in history into the 116th Congress. Or billionaire Robert F. Smith’s pledge to pay off every Morehouse College (in Atlanta, Georgia) student’s debt. Indeed, there are many good people helping and great moments happening in spite of a bleak 24-hour news cycle designed to ruin happiness and to limit our understanding of our human potential. We at Witness see this yearning for transformation in the works we selected. The doorway must be crossed, and the voices and characters we featured in our Winter 2019 issue stand at the vestibule, ready for the light to warm them, primed to fight for that necessary illumination.https://digitalscholarship.unlv.edu/witness/1000/thumbnail.jp
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