3,314 research outputs found
The secular evolution of the Kuiper belt after a close stellar encounter
We show the effects of the perturbation caused by a passing by star on the
Kuiper belt objects (KBOs) of our Solar System. The dynamics of the Kuiper belt
(KB) is followed by direct -body simulations. The sampling of the KB has
been done with up to , setting the KBOs on initially nearly
circular orbits distributed in a ring of surface density .
This modelization allowed us to investigate the secular evolution of the KB
upon the encounter with the perturbing star. Actually, the encounter itself
usually leads toward eccentricity and inclination distributions similar to
observed ones, but tends also to excite the low-eccentricity population ( around \, from the Sun), depleting this region of
low eccentricities. The following long-term evolution shows a "cooling" of the
eccentricities repopulating the low-eccentricity area. In dependence on the
assumed KBO mass spectrum and sampled number of bodies, this repopulation takes
place in a time that goes from 0.5 Myr to 100 Myr. Due to the unavoidable
limitation in the number of objects in our long-term simulations (), we could not consider a detailed KBO mass spectrum, accounting for low
mass objects, thus our present simulations are not reliable in constraining
correlations among inclination distribution of the KBOs and other properties,
such as their size distribution. However, our high precision long term
simulations are a starting point for future larger studies on massively
parallel computational platforms which will provide a deeper investigation of
the secular evolution (Myr) of the KB over its whole mass spectrum.Comment: 13 pages, 12 figures, 5 table
Fun for Two
We performed populations synthesis calculations of single stars and binaries
and show that binary evolution is extremely important for Galactic astronomy.
We review several binary evolution models and conclude that they give quite
different results. These differences can be understood from the assumptions
related to how mass is transfered in the binary systems. Most important are 1)
the fraction of mass that is accreted by the companion star during mass
transfer, 2) the amount of specific angular momentum which is carried away with
the mass that leaves the binary system.Comment: 7 pages, 0 figures to appear in the proceeding of the IAU Symposium
200, "The Formation of Binary Stars" eds. H. Zinnecker and R. Mathie
Reconstructing the evolution of double helium white dwarfs: envelope loss without spiral-in
The unique core-mass - radius relation for giants with degenerate helium
cores enables us to reconstruct the evolution of three observed double helium
white dwarfs with known masses of both components.
The last mass transfer phase in their evolution must have been a spiral-in.
In the formalism proposed by Webbink (1984), we can constrain the efficiency of
the deposition of orbital energy into the envelope to be 1 \la \alpha \la 6,
for an envelope structure parameter . We find that the two
standard mass transfer types (stable mass transfer and spiral-in) are both
unable to explain the first phase of mass transfer for these three binaries.
We use a parametric approach to describe mass transfer in low-mass binaries,
where both stars are of comparable mass and find that the orbital
characteristics of the observed double helium white dwarfs can be well
reproduced if the envelope of the primary is lost with ~1.5 times the specific
angular momentum of the initial binary. In this case no substantial spiral-in
occurs.Comment: 8 pages, accepted for publication in A&
A pilgrimage to gravity on GPUs
In this short review we present the developments over the last 5 decades that
have led to the use of Graphics Processing Units (GPUs) for astrophysical
simulations. Since the introduction of NVIDIA's Compute Unified Device
Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body
simulations and is so popular these days that almost all papers about high
precision N-body simulations use methods that are accelerated by GPUs. With the
GPU hardware becoming more advanced and being used for more advanced algorithms
like gravitational tree-codes we see a bright future for GPU like hardware in
computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer
Simulations on Graphics Processing Units" . 18 pages, 8 figure
Comparing compact binary parameter distributions I: Methods
Being able to measure each merger's sky location, distance, component masses,
and conceivably spins, ground-based gravitational-wave detectors will provide a
extensive and detailed sample of coalescing compact binaries (CCBs) in the
local and, with third-generation detectors, distant universe. These
measurements will distinguish between competing progenitor formation models. In
this paper we develop practical tools to characterize the amount of
experimentally accessible information available, to distinguish between two a
priori progenitor models. Using a simple time-independent model, we demonstrate
the information content scales strongly with the number of observations. The
exact scaling depends on how significantly mass distributions change between
similar models. We develop phenomenological diagnostics to estimate how many
models can be distinguished, using first-generation and future instruments.
Finally, we emphasize that multi-observable distributions can be fully
exploited only with very precisely calibrated detectors, search pipelines,
parameter estimation, and Bayesian model inference
Simple Stellar Population Models as probed by the Large Magellanic Cloud Star Cluster ESO 121-SC03
The presence of blue straggler stars (BSs) in star clusters has proven a
challenge to conventional simple stellar population (SSP) models. Conventional
SSP models are based on the evolution theory of single stars. Meanwhile, the
typical locations of BSs in the colour-magnitude diagram of a cluster are
brighter and bluer than the main sequence turn-off point. Such loci cannot be
predicted by single-star evolution theory. However, stars with such properties
contribute significantly to the integrated light of the cluster. In this paper,
we reconstruct the integrated properties of the Large Magellanic Cloud cluster
ESO 121-SC03, based on a detailed exploration of the individual cluster stars,
and with particular emphasis on the cluster's BSs. We find that the integrated
light properties of ESO 121-SC03 are dramatically modified by its BS component.
The integrated spectral energy distribution (ISED) flux level is significantly
enhanced toward shorter wavelengths, and all broad-band colours become bluer.
When fitting the fully integrated ISED of this cluster based on conventional
SSP models, the best-fitting values of age and metallicity are significantly
underestimated compared to the true cluster parameters. The age underestimate
is per cent if we only include the BSs within the cluster's half-light
radius and per cent if all BSs are included. The corresponding
underestimates of the cluster's metallicity are and per cent,
respectively. The populous star clusters in the Magellanic Clouds are ideal
objects to explore the potential importance of BSs for the integrated light
properties of more distant unresolved star clusters in a statistically robust
manner, since they cover a large range in age and metallicity.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in MNRA
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