1,298 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 formation and dynamical evolution of young star clusters
Recent observations have revealed a variety of young star clusters, including
embedded systems, young massive clusters, and associations. We study the
formation and dynamical evolution of these clusters using a combination of
simulations and theoretical models. Our simulations start with a turbulent
molecular cloud that collapses under its own gravity. The stars are assumed to
form in the densest regions in the collapsing cloud after an initial free-fall
times of the molecular cloud. The dynamical evolution of these stellar
distributions are continued by means of direct -body simulations. The
molecular clouds typical for the Milky Way Galaxy tend to form embedded
clusters which evolve to resemble open clusters. The associations were
initially considerably more clumpy, but lost their irregularity in about a
dynamical time scale due to the relaxation process. The densest molecular
clouds, which are absent in the Milky Way but are typical in starburst
galaxies, form massive young star clusters. They indeed are rare in the Milky
Way. Our models indicate a distinct evolutionary path from molecular clouds to
open clusters and associations or to massive star clusters. The mass-radius
relation for both types of evolutionary tracks excellently matches the
observations. According to our calculations the time evolution of the half-mass
radius for open clusters and associations follows , whereas for massive star clusters . Both trends are consistent with
the observed age-mass-radius relation for clusters in the Milky Way.Comment: 16 pages, 9 figures, accepted for publication in Ap
A debris disk under the influence of a wide planetary mass companion: The system of HD106906
The 13 Myr old star HD106906 is orbited by a debris disk of at least 0.067
M_Moon with an inner and outer radius of 20 AU and 120 AU, respectively, and by
a planet at a distance of 650 AU. We use this curious combination of a close
low-mass disk and a wide planet to motivate our simulations of this system. We
study the parameter space of the initial conditions to quantify the mass loss
from the debris disk and its lifetime under the influence of the planet. We
find that when the planet orbits closer to the star than about 50 AU and with
low inclination relative to the disk (less than about 10 degrees), more disk
material is perturbed outside than inside the region constrained by
observations on timescales shorter than 1 Myr. Considering the age of the
system, such a short lifetime of the disk is incompatible with the timescale
for planet--planet scattering which is one of the scenarios suggested to
explain the wide separation of the planet. For some configurations when the
planet's orbit is inclined with respect to the disk, the latter will start to
wobble. We argue that this wobbling is caused by a mechanism similar to the
Kozai--Lidov oscillations. We also observe various resonant structures (such as
rings and spiral arms) induced in the disk by the planet.Comment: 10 pages, 9 figures, accepted for publication in MNRA
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