146 research outputs found
High performance astrophysics computing
The application of high end computing to astrophysical problems, mainly in
the galactic environment, is under development since many years at the Dep. of
Physics of Sapienza Univ. of Roma. The main scientific topic is the physics of
self gravitating systems, whose specific subtopics are: i) celestial mechanics
and interplanetary probe transfers in the solar system; ii) dynamics of
globular clusters and of globular cluster systems in their parent galaxies;
iii) nuclear clusters formation and evolution; iv) massive black hole formation
and evolution; v) young star cluster early evolution. In this poster we
describe the software and hardware computational resources available in our
group and how we are developing both software and hardware to reach the
scientific aims above itemized.Comment: 2 pages paper presented at the Conference "Advances in Computational
Astrophysics: methods, tools and outcomes", to be published in the ASP
Conference Series, 2012, vol. 453, R. Capuzzo-Dolcetta, M. Limongi and A.
Tornambe' ed
A Monte Carlo analysis of the velocity dispersion of the globular cluster Palomar 14
We present the results of a detailed analysis of the projected velocity
dispersion of the globular cluster Palomar 14 performed using recent
high-resolution spectroscopic data and extensive Monte Carlo simulations. The
comparison between the data and a set of dynamical models (differing in
fraction of binaries, degree of anisotropy, mass-to-light ratio M/L, cluster
orbit and theory of gravity) shows that the observed velocity dispersion of
this stellar system is well reproduced by Newtonian models with a fraction of
binaries f_b<30% and a M/L compatible with the predictions of stellar evolution
models. Instead, models computed with a large fraction of binaries
systematically overestimate the cluster velocity dispersion. We also show that,
across the parameter space sampled by our simulations, models based on the
Modified Newtonian Dynamics theory can be reconciled with observations only
assuming values of M/L lower than those predicted by stellar evolution models
under standard assumptions.Comment: 13 pages, 13 figures, accepted for publication by Ap
Jeans modelling of the Milky Way's nuclear stellar disc
The nuclear stellar disc (NSD) is a flattened stellar structure that dominates the gravitational potential of the Milky Way at Galactocentric radii 30âČRâČ300pcâ . In this paper, we construct axisymmetric Jeans dynamical models of the NSD based on previous photometric studies and we fit them to line-of-sight kinematic data of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and silicon monoxide (SiO) maser stars. We find that (i) the NSD mass is lower but consistent with the mass independently determined from photometry by Launhardt et al. Our fiducial model has a mass contained within spherical radius r=100pc of M(r 1. Observations and theoretical models of the star-forming molecular gas in the central molecular zone suggest that large vertical oscillations may be already imprinted at stellar birth. However, the finding Ïz/ÏR > 1 depends on a drop in the velocity dispersion in the innermost few tens of parsecs, on our assumption that the NSD is axisymmetric, and that the available (extinction corrected) stellar samples broadly trace the underlying light and mass distributions, all of which need to be established by future observations and/or modelling. (iii) We provide the most accurate rotation curve to date for the innermost 500pc of our Galaxy
NBSymple, a double parallel, symplectic N-body code running on Graphic Processing Units
We present and discuss the characteristics and performances, both in term of
computational speed and precision, of a numerical code which numerically
integrates the equation of motions of N 'particles' interacting via Newtonian
gravitation and move in an external galactic smooth field. The force evaluation
on every particle is done by mean of direct summation of the contribution of
all the other system's particle, avoiding truncation error. The time
integration is done with second-order and sixth-order symplectic schemes. The
code, NBSymple, has been parallelized twice, by mean of the Computer Unified
Device Architecture to make the all-pair force evaluation as fast as possible
on high-performance Graphic Processing Units NVIDIA TESLA C 1060, while the
O(N) computations are distributed on various CPUs by mean of OpenMP Application
Program. The code works both in single precision floating point arithmetics or
in double precision. The use of single precision allows the use at best of the
GPU performances but, of course, limits the precision of simulation in some
critical situations. We find a good compromise in using a software
reconstruction of double precision for those variables that are most critical
for the overall precision of the code. The code is available on the web site
astrowww.phys.uniroma1.it/dolcetta/nbsymple.htmlComment: Paper composed by 29 pages, including 9 figures. Submitted to New
Astronomy
Smooth kinematic and metallicity gradients between the Milky Way's nuclear star cluster and nuclear stellar disc. Different components of the same structure?
The innermost regions of most galaxies are characterised by the presence of
extremely dense nuclear star clusters. Nevertheless, these clusters are not the
only stellar component present in galactic nuclei, where larger stellar
structures known as nuclear stellar discs, have also been found. Understanding
the relation between nuclear star clusters and nuclear stellar discs is
challenging due to the large distance towards other galaxies which limits their
analysis to integrated light. The Milky Way's centre, at only 8 kpc, hosts a
nuclear star cluster and a nuclear stellar disc, constituting a unique template
to understand their relation and formation scenario. We aim to study the
kinematics and stellar metallicity of stars from the Milky Way's nuclear star
cluster and disc to shed light on the relation between these two Galactic
centre components. We used publicly available photometric, proper motions, and
spectroscopic catalogues to analyse a region of centred on
the Milky Way's nuclear star cluster. We built colour magnitude diagrams, and
applied colour cuts to analyse the kinematic and metallicity distributions of
Milky Way's nuclear star cluster and disc stars with different extinction along
the line of sight. We detect kinematics and metallicity gradients for the
analysed stars along the line of sight towards the Milky Way's nuclear star
cluster, suggesting a smooth transition between the nuclear stellar disc and
cluster. We also find a bi-modal metallicity distribution for all the analysed
colour bins, which is compatible with previous work on the bulk population of
the nuclear stellar disc and cluster. Our results suggest that these two
Galactic centre components might be part of the same structure with the Milky
Way's nuclear stellar disc being the grown edge of the nuclear star cluster.Comment: Submitted to A&A. 13 pages, 9 figure
Gaia and Hubble unveil the kinematics of stellar populations in the Type II globular clusters {\omega} Centauri and M 22
The origin of multiple stellar populations in Globular Clusters (GCs) is one
of the greatest mysteries of modern stellar astrophysics. N-body simulations
suggest that the present-day dynamics of GC stars can constrain the events that
occurred at high redshift and led to the formation of multiple populations.
Here, we combine multi-band photometry from the Hubble Space Telescope (HST)
and ground-based facilities with HST and Gaia Data Release 2 proper motions to
investigate the spatial distributions and the motions in the plane of the sky
of multiple populations in the type II GCs NGC 5139 (Centauri) and
NGC 6656 (M 22). We first analyzed stellar populations with different
metallicities. Fe-poor and Fe-rich stars in M 22 share similar spatial
distributions and rotation patterns and exhibit similar isotropic motions.
Similarly, the two main populations with different iron abundance in
Centauri share similar ellipticities and rotation patterns. When
analyzing different radial regions, we find that the rotation amplitude
decreases from the center towards the external regions. Fe-poor and Fe-rich
stars of Centauri are radially anisotropic in the central region and
show similar degrees of anisotropy. We also investigate the stellar populations
with different light-element abundances and find that their N-rich stars
exhibit higher ellipticity than N-poor stars. In Centauri Centauri
both stellar groups are radially anisotropic. Interestingly, N-rich, Fe-rich
stars exhibit different rotation patterns than N-poor stars with similar
metallicities. The stellar populations with different nitrogen of M 22 exhibit
similar rotation patterns and isotropic motions. We discuss these findings in
the context of the formation of multiple populations.Comment: 24 pages, 13 figures, accepted for publication in Ap
A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations
The Sagittarius dwarf spheroidal galaxy is in an advanced stage of disruption but still hosts its nuclear star cluster (NSC), M54, at its center. In this paper, we present a detailed kinematic characterization of the three stellar populations present in M54: young metal-rich (YMR); intermediate-age metal-rich (IMR); and old metal-poor (OMP), based on the spectra of ~6500 individual M54 member stars extracted from a large Multi-Unit Spectroscopic Explorer (MUSE)/Very Large Telescope data set. We find that the OMP population is slightly flattened with a low amount of rotation (~0.8 km sâ1) and with a velocity dispersion that follows a Plummer profile. The YMR population displays a high amount of rotation (~5 km sâ1) and a high degree of flattening, with a lower and flat velocity dispersion profile. The IMR population shows a high but flat velocity dispersion profile, with some degree of rotation (~2 km sâ1). We complement our MUSE data with information from Gaia DR2 and confirm that the stars from the OMP and YMR populations are comoving in 3D space, suggesting that they are dynamically bound. While dynamical evolutionary effects (e.g., energy equipartition) are able to explain the differences in velocity dispersion between the stellar populations, the strong differences in rotation indicate different formation paths for the populations, as supported by an N-body simulation tailored to emulate the YMRâOMP system. This study provides additional evidence for the M54 formation scenario proposed in our previous work, where this NSC formed via GC accretion (OMP) and in situ formation from gas accretion in a rotationally supported disk (YMR)
The Unexpected Kinematics of Multiple Populations in NGC 6362: Do Binaries Play a Role?
We present a detailed analysis of the kinematic properties of the multiple populations (MPs) in the low-mass Galactic globular cluster (GC) NGC 6362 based on a sample of about 500 member stars for which radial velocities (RVs), and Fe and Na abundances have been homogeneously derived. At distances from the cluster center larger than about 0.5r h , we find that first-generation (FGâNa-poor) and second-generation (SGâNa-rich) stars show hints of different line-of-sight velocity dispersion profiles, with FG stars being dynamically hotter. This is the first time that differences in the velocity dispersion of MPs are detected using only RVs. While kinematic differences between MPs in GCs are usually described in terms of anisotropy differences driven by the different radial distributions, this explanation hardly seems viable for NGC 6362, where SG and FG stars are spatially mixed. We demonstrate that the observed difference in the velocity dispersion profiles can be accounted for by the effect of binary stars. In fact, thanks to our multi-epoch RV measurements, we find that the binary fraction is significantly larger in the FG sample (f ~ 14%) than in the SG population (f < 1%), and we show that such a difference can inflate the velocity dispersion of FG with respect to SG by the observed amount in the relevant radial range. Our results nicely match the predictions of state-of-the art N-body simulations of the co-evolution of MPs in GCs that include the effects of binaries
The Galactic Center Black Hole Laboratory
The super-massive 4 million solar mass black hole Sagittarius~A* (SgrA*)
shows flare emission from the millimeter to the X-ray domain. A detailed
analysis of the infrared light curves allows us to address the accretion
phenomenon in a statistical way. The analysis shows that the near-infrared
flare amplitudes are dominated by a single state power law, with the low states
in SgrA* limited by confusion through the unresolved stellar background. There
are several dusty objects in the immediate vicinity of SgrA*. The source G2/DSO
is one of them. Its nature is unclear. It may be comparable to similar stellar
dusty sources in the region or may consist predominantly of gas and dust. In
this case a particularly enhanced accretion activity onto SgrA* may be expected
in the near future. Here the interpretation of recent data and ongoing
observations are discussed.Comment: 30 pages - 7 figures - accepted for publication by Springer's
"Fundamental Theories of Physics" series; summarizing GC contributions of 2
conferences: 'Equations of Motion in Relativistic Gravity' at the
Physikzentrum Bad Honnef, Bad Honnef, Germany, (Feb. 17-23, 2013) and the
COST MP0905 'The Galactic Center Black Hole Laboratory' Granada, Spain (Nov.
19 - 22, 2013
Gaia Data Release 3: G_RVS photometry from the RVS spectra
Gaia Data Release 3 (DR3) contains the first release of magnitudes estimated
from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample
of about 32.2 million stars brighter than G_RVS~14 mag (or G~15 mag). In this
paper, we describe the data used and the approach adopted to derive and
validate the G_RVS magnitudes published in DR3. We also provide estimates of
the G_RVS passband and associated G_RVS zero-point. We derived G_RVS photometry
from the integration of RVS spectra over the wavelength range from 846 to 870
nm. We processed these spectra following a procedure similar to that used for
DR2, but incorporating several improvements that allow a better estimation of
G_RVS. These improvements pertain to the stray-light background estimation, the
line spread function calibration, and the detection of spectra contaminated by
nearby relatively bright sources. We calibrated the G_RVS zero-point every 30
hours based on the reference magnitudes of constant stars from the Hipparcos
catalogue, and used them to transform the integrated flux of the cleaned and
calibrated spectra into epoch magnitudes. The G_RVS magnitude of a star
published in DR3 is the median of the epoch magnitudes for that star. We
estimated the G_RVS passband by comparing the RVS spectra of 108 bright stars
with their flux-calibrated spectra from external spectrophotometric libraries.
The G_RVS magnitude provides information that is complementary to that obtained
from the G, G_BP, and G_RP magnitudes, which is useful for constraining stellar
metallicity and interstellar extinction. The median precision of G_RVS
measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5
< G_RVS < 6.5 mag) to 0.125 mag at the faint end. The derived G_RVS passband
shows that the effective transmittance of the RVS is approximately 1.23 times
better than the pre-launch estimate.Comment: 16 pages, 18 figures. Accepted for publication in A&
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