234 research outputs found
Phase refinement and extension by means of non-crystallographic symmetry averaging using parallel computers
Compact stellar systems in the Fornax cluster: a UV perspective
In recent years, increasing evidence for chemical complexity and multiple
stellar populations in massive globular clusters (GCs) has emerged, including
extreme horizontal branches (EHBs) and UV excess. Our goal is to improve our
understanding of UV excess in the regime of both massive GCs and ultra-compact
dwarf galaxies (UCDs). To this end, we use deep archival GALEX data of the
central Fornax cluster to measure NUV and FUV magnitudes of UCDs and massive
GCs. We obtain NUV photometry for a sample of 35 compact objects with
-13.5<M_V<-10 mag. Of those, 21 objects also have FUV photometry. Roughly half
of the sources fall into the UCD luminosity regime (M_V <=-11 mag). We find
that seven out of 17 massive Fornax GCs exhibit a NUV excess with respect to
expectations from stellar population models, even for models with enhanced
Helium abundance. This suggests that not only He-enrichment has contributed to
forming the EHB population of these GCs. The GCs extend to stronger UV excess
than GCs in M31 and massive GCs in M87, at the 97% confidence level. Most of
the UCDs with FUV photometry also show evidence for UV excess, but their UV
colours can be matched by isochrones with enhanced Helium abundances and old
ages 12-14 Gyrs. We find that Fornax compact objects with X-ray emission
detected from Chandra images are almost disjunct in colour from compact objects
with GALEX UV detection, with only one X-ray source among the 35 compact
objects. However, since this source is one of the three most UV bright GCs, we
cannot exclude that the physical processes causing X-ray emission also
contribute to some of the observed UV excess.Comment: Research Note, 7 pages, 3 figures, accepted for publication in A&
Structural Studies of Ferrofluids by Small-Angle Neutron Scattering
Abstract. The aim of this paper is to present method to investigate the properties of magnetic fluids by means of small angle neutron scattering. Ferrofluids are dispersions of small, single-domain magnetic particles suspended in a fluid carrier. The neutron scattering methods have been largely used the last two decades for the determination of structural properties of magnetic liquids at microscopic level. There can be investigated the structure of the particle, the aggregation phenomena, the magnetic liquid dynamics, particle-surfactant interaction, surfactant liquid-base interaction and structure, magnetic behavior of the samples. Experiments on small angle neutron scattering were carried out on SANS instrument YuMO in function at IBR-2 high-pulsed reactor at the Fran
The nucleus of the Sagittarius dSph galaxy and M54: a window on the process of galaxy nucleation
We present the results of a thorough study of the nucleus of the Sgr dwarf
spheroidal galaxy and of the bright globular cluster M54 that resides within
the same nucleus (Sgr,N). We have obtained accurate radial velocities and
metallicity estimates for 1152 candidate Red Giant Branch stars of Sgr and M54
lying within ~ 9 arcmin from the center of the galaxy, from Keck/DEIMOS and
VLT/FLAMES spectra of the infrared Calcium II triplet. Using both velocity and
metallicity information we selected two samples of 425 and 321 very-likely
members of M54 and of Sgr,N, respectively. The two considered systems display
significantly different velocity dispersion profiles: M54 has a steeply
decreasing profile from r=0, where sigma= 14.2 km/s, to r=3.5 arcmin where it
reaches sigma=5.3 km/s, then it appears to rise again to sigma= 10 km/s at r=7
arcmin. In contrast Sgr,N has a uniformly flat profile at sigma=9.6 km/s over
the whole 0 < r < 9 arcmin range. Using data from the literature we show that
the velocity dispersion of Sgr remains constant at least out to r ~ 100 arcmin
and there is no sign of the transition between the outer
flat-luminosity-profile core and the inner nucleus in the velocity profile.
These results - together with a re-analysis of the surface brightness profile
of Sgr,N and a suite of dedicated N-body simulations - provide very strong
support for the hypothesis that the nucleus of Sgr formed independently of M54,
which probably plunged to its present position, coincident with Sgr,N, because
of significant decay of the original orbit due to dynamical friction.Comment: Accepted for publication by the Astronomical Journal. emulateapj.cls,
26 pag., 21 low resolution figures. A full-resolution color version of the
paper can be retrieved from http://www.bo.astro.it/SGR/Sgr_nucleus.ps.g
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
Dissolution is the solution: on the reduced mass-to-light ratios of Galactic globular clusters
The observed dynamical mass-to-light (M/L) ratios of globular clusters (GCs)
are systematically lower than those expected from `canonical' simple stellar
population models, which do not account for the preferential loss of low-mass
stars due to energy equipartition. It was recently shown that low-mass star
depletion can qualitatively explain the M/L discrepancy. To verify whether it
is indeed the driving mechanism, we derive dissolution timescales and use these
to predict the M/L_V ratios of the 24 Galactic GCs for which orbital parameters
and dynamical M/L_V are known. We also predict the slopes of their low-mass
stellar mass functions (MFs). We use the SPACE cluster models, which include
dynamical dissolution, low-mass star depletion, stellar evolution, stellar
remnants and various metallicities. The predicted M/L_V are in 1 sigma
agreement with the observations for 12 out of 24 GCs. The discrepancy for the
other GCs probably arises because our predictions give global M/L ratios, while
the observations represent extrapolated central values that are different from
global ones in case of mass segregation and a long dissolution timescale. GCs
in our sample which likely have dissimilar global and central M/L ratios can be
excluded by imposing limits on the dissolution timescale and King parameter.
For the remaining GCs, the observed and predicted average M/L_V are 78^+9_-11%
and 78+/-2% of the canonically expected values, while for the entire sample the
values are 74^+6_-7% and 85+/-1%. The predicted correlation between the slope
of the low-mass stellar MF and M/L_V is qualitatively consistent with observed
MF slopes. It is concluded that the variation of M/L ratio due to dissolution
and low-mass star depletion is a plausible explanation for the discrepancy
between the observed and canonically expected M/L ratios of GCs. (Abridged)Comment: 17 pages, 10 figures, 6 tables; paper accepted for publication in A&
A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE
In this small note we are concerned with the solution of Forward-Backward
Stochastic Differential Equations (FBSDE) with drivers that grow quadratically
in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem
is a comparison result that allows comparing componentwise the signs of the
control processes of two different qgFBSDE. As a byproduct one obtains
conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio
Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at , 2.76 and 7 TeV
Measurements of the sphericity of primary charged particles in minimum bias
proton--proton collisions at , 2.76 and 7 TeV with the ALICE
detector at the LHC are presented. The observable is linearized to be collinear
safe and is measured in the plane perpendicular to the beam direction using
primary charged tracks with GeV/c in . The
mean sphericity as a function of the charged particle multiplicity at
mid-rapidity () is reported for events with different
scales ("soft" and "hard") defined by the transverse momentum of the leading
particle. In addition, the mean charged particle transverse momentum versus
multiplicity is presented for the different event classes, and the sphericity
distributions in bins of multiplicity are presented. The data are compared with
calculations of standard Monte Carlo event generators. The transverse
sphericity is found to grow with multiplicity at all collision energies, with a
steeper rise at low , whereas the event generators show the
opposite tendency. The combined study of the sphericity and the mean with multiplicity indicates that most of the tested event generators
produce events with higher multiplicity by generating more back-to-back jets
resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with
tune PERUGIA-2011 exhibits a noticeable improvement in describing the data,
compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16,
published version, figures from
http://aliceinfo.cern.ch/ArtSubmission/node/308
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
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