2,778 research outputs found
The Formation of Solar System Analogs in Young Star Clusters
The Solar system was once rich in the short-lived radionuclide (SLR)
Al\, but deprived in Fe. Several models have been proposed to
explain these anomalous abundances in SLRs, but none has been set within a
self-consistent framework of the evolution of the Solar system and its birth
environment. The anomalous abundance in Al may have originated from the
accreted material in the wind of a massive \apgt 20\, Wolf-Rayet
star, but the star could also have been a member of the parental star-cluster
instead of an interloper or an older generation that enriched the proto-solar
nebula. The protoplanetary disk at that time was already truncated around the
Kuiper-cliff (at au) by encounters with another cluster members before it
was enriched by the wind of the nearby Wolf-Rayet star. The supernova explosion
of a nearby star, possibly but not necessarily the exploding Wolf-Rayet star,
heated the disk to \apgt 1500K, melting small dust grains and causing the
encapsulation and preservation of Al into vitreous droplets. This
supernova, and possibly several others, caused a further abrasion of the disk
and led to its observed tilt of with respect to the Sun's
equatorial plane. The abundance of Fe originates from a supernova shell,
but its preservation results from a subsequent supernova. At least two
supernovae are needed (one to deliver Fe\, and one to preserve it in the
disk) to explain the observed characteristics of the Solar system. The most
probable birth cluster then has stars and a radius of pc. We conclude that Solar systems equivalent systems form
in the Milky Way Galaxy at a rate of about 30 per Myr, in which case
approximately 36,000 Solar system analogues roam the Milky Way.Comment: Submitted to A&
Stellar disk destruction by dynamical interactions in the Orion Trapezium star cluster
We compare the observed size distribution of circum stellar disks in the
Orion Trapezium cluster with the results of -body simulations in which we
incorporated an heuristic prescription for the evolution of these disks. In our
simulations, the sizes of stellar disks are affected by close encounters with
other stars (with disks). We find that the observed distribution of disk sizes
in the Orion Trapezium cluster is excellently reproduced by truncation due to
dynamical encounters alone. The observed distribution appears to be a sensitive
measure of the past dynamical history of the cluster, and therewith on the
conditions of the cluster at birth. The best comparison between the observed
disk size distribution and the simulated distribution is realized with a
cluster of stars with a half-mass radius of about 0.5\,pc in
virial equilibrium (with a virial ratio of , or somewhat colder ), and with a density structure according to a fractal dimension of
. Simulations with these parameters reproduce the observed
distribution of circum stellar disks in about 0.2--0.5\,Myr.Comment: submitted to MNRA
The origin of the two populations of blue stragglers in M30
We analyze the position of the two populations of blue stragglers in the
globular cluster M30 in the Hertzsprung-Russell diagram. Both populations of
blue stragglers are brighter than the cluster's turn-off, but one population
(the blue blue-stragglers) align along the zero-age main-sequence whereas the
(red) population is elevated in brightness (or colour) by mag.
Based on stellar evolution and merger simulations we argue that the red
population, which composes about 40\% of the blue stragglers in M 30, is formed
at a constant rate of blue stragglers per Gyr over the last Gyr. The blue population is formed in a burst that started Gyr
ago at a peak rate of blue stragglers per Gyr with an e-folding
time scale of Gyr. We speculate that the burst resulted from the core
collapse of the cluster at an age of about 9.8 Gyr, whereas the constantly
formed population is the result of mass transfer and mergers through binary
evolution. In that case about half the binaries in the cluster effectively
result in a blue straggler.Comment: Accepted for publication as Letter in A&
The lost siblings of the Sun
The anomalous chemical abundances and the structure of the Edgewood-Kuiper
belt observed in the solar system constrain the initial mass and radius of the
star cluster in which the sun was born to to 3000 \msun and
to 3 pc. When the cluster dissolved the siblings of the sun
dispersed through the galaxy, but they remained on a similar orbit around the
Galactic center. Today these stars hide among the field stars, but 10 to 60 of
them are still present within a distance of pc. These siblings of
the sun can be identified by accurate measurements of their chemical
abundances, positions and their velocities. Finding even a few will strongly
constrain the parameters of the parental star cluster and the location in the
Galaxy where we were born.Comment: Submitted to ApJ Letter
A new type of compact stellar population: dark star clusters
Among the most explored directions in the study of dense stellar systems is
the investigation of the effects of the retention of supernova remnants,
especially that of the massive stellar remnant black holes (BHs), in star
clusters. By virtue of their eventual high central concentration, these stellar
mass BHs potentially invoke a wide variety of physical phenomena, the most
important ones being emission of gravitational waves (GWs), formation of X-ray
binaries, and modification of the dynamical evolution of the cluster. Here we
propose, for the first time, that rapid removal of stars from the outer parts
of a cluster by the strong tidal field in the inner region of our Galaxy can
unveil its BH sub-cluster, which appears as a star cluster that is
gravitationally bound by an invisible mass. We study the formation and
properties of such systems through direct N-body computations and estimate that
they can be present in significant numbers in the inner region of the Milky
Way. We call such objects "dark star clusters" (DSCs) as they appear dimmer
than normal star clusters of similar mass and they comprise a predicted, new
class of entities. The finding of DSCs will robustly cross-check BH retention;
they will not only constrain the uncertain natal kicks of BHs, thereby the
widely debated theoretical models of BH formation, but will also pinpoint star
clusters as potential sites for GW emission for forthcoming ground-based
detectors such as the Advanced LIGO. Finally, we also discuss the relevance of
DSCs for the nature of IRS 13E.Comment: 14 pages, 4 figures. Published in The Astrophysical Journal Letter
SAPPORO: A way to turn your graphics cards into a GRAPE-6
We present Sapporo, a library for performing high-precision gravitational
N-body simulations on NVIDIA Graphical Processing Units (GPUs). Our library
mimics the GRAPE-6 library, and N-body codes currently running on GRAPE-6 can
switch to Sapporo by a simple relinking of the library. The precision of our
library is comparable to that of GRAPE-6, even though internally the GPU
hardware is limited to single precision arithmetics. This limitation is
effectively overcome by emulating double precision for calculating the distance
between particles. The performance loss of this operation is small (< 20%)
compared to the advantage of being able to run at high precision. We tested the
library using several GRAPE-6-enabled N-body codes, in particular with Starlab
and phiGRAPE. We measured peak performance of 800 Gflop/s for running with 10^6
particles on a PC with four commercial G92 architecture GPUs (two GeForce
9800GX2). As a production test, we simulated a 32k Plummer model with equal
mass stars well beyond core collapse. The simulation took 41 days, during which
the mean performance was 113 Gflop/s. The GPU did not show any problems from
running in a production environment for such an extended period of time.Comment: 13 pages, 9 figures, accepted to New Astronom
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