576 research outputs found
Isolation and Characterization of Eight Polymorphic Microsatellites for the Spotted Spiny Lobster, Panulirus guttatus
Microsatellite sequences were isolated from enriched genomic libraries of the spotted spiny lobster, Panulirus guttatus using 454 pyrosequencing. Twenty-nine previously developed polymerase chain reaction primer pairs of Panulirus argus microsatellite loci were also tested for cross-species amplification in Panulirus guttatus. In total, eight consistently amplifying, and polymorphic loci were characterized for 57 individuals collected in the Florida Keys and Bermuda. The number of alleles per locus ranged from 8 to 20 and observed heterozygosities ranged from 0.409 to 0.958. Significant deviations from Hardy–Weinberg equilibrium were found in one locus from Florida and three loci from Bermuda. Quality control testing indicated that all loci were easy to score, highly polymorphic and showed no evidence of linkage disequilibrium. Null alleles were detected in three loci with moderate frequencies ranging from (20% to 22%). These eight microsatellites provide novel molecular markers for future conservation genetics research of P. guttatus
A Chandra Observation of Supernova Remnant G350.1-0.3 and Its Central Compact Object
We present a new Chandra observation of supernova remnant (SNR) G350.1-0.3.
The high resolution X-ray data reveal previously unresolved filamentary
structures and allow us to perform detailed spectroscopy in the diffuse regions
of this SNR. Spectral analysis demonstrates that the region of brightest
emission is dominated by hot, metal-rich ejecta while the ambient material
along the perimeter of the ejecta region and throughout the remnant's western
half is mostly low-temperature, shocked interstellar/circumstellar medium
(ISM/CSM) with solar-type composition. The data reveal that the emission
extends far to the west of the ejecta region and imply a lower limit of 6.6 pc
on the diameter of the source (at a distance of 4.5 kpc). We show that
G350.1-0.3 is likely in the free expansion (ejecta-dominated) stage and
calculate an age of 600-1200 years. The derived relationship between the shock
velocity and the electron/proton temperature ratio is found to be entirely
consistent with that of other SNRs. We perform spectral fits on the X-ray
source XMMU J172054.5-372652, a candidate central compact object (CCO), and
find that its spectral properties fall within the typical range of other CCOs.
We also present archival 24 um data of G350.1-0.3 taken with the Spitzer Space
Telescope during the MIPSGAL galactic survey and find that the infrared and
X-ray morphologies are well-correlated. These results help to explain this
remnant's peculiar asymmetries and shed new light on its dynamics and
evolution
An adjustable law of motion for relativistic spherical shells
A classical and a relativistic law of motion for an advancing shell are
deduced applying the thin layer approximation. A new parameter connected with
the quantity of absorbed matter in the expansion is introduced; this allows of
matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal
of Physics 201
Turbulent Mixing in the Interstellar Medium -- an application for Lagrangian Tracer Particles
We use 3-dimensional numerical simulations of self-gravitating compressible
turbulent gas in combination with Lagrangian tracer particles to investigate
the mixing process of molecular hydrogen (H2) in interstellar clouds. Tracer
particles are used to represent shock-compressed dense gas, which is associated
with H2. We deposit tracer particles in regions of density contrast in excess
of ten times the mean density. Following their trajectories and using
probability distribution functions, we find an upper limit for the mixing
timescale of H2, which is of order 0.3 Myr. This is significantly smaller than
the lifetime of molecular clouds, which demonstrates the importance of the
turbulent mixing of H2 as a preliminary stage to star formation.Comment: 10 pages, 5 figures, conference proceedings "Turbulent Mixing and
Beyond 2007
The Nucleosynthetic Imprint of 15-40 Solar Mass Primordial Supernovae on Metal-Poor Stars
The inclusion of rotationally-induced mixing in stellar evolution can alter
the structure and composition of presupernova stars. We survey the effects of
progenitor rotation on nucleosynthetic yields in Population III and II
supernovae using the new adaptive mesh refinement (AMR) code CASTRO. We examine
spherical explosions in 15, 25 and 40 solar mass stars at Z = 0 and 10^-4 solar
metallicity with three explosion energies and two rotation rates. Rotation in
the Z = 0 models resulted in primary nitrogen production and a stronger
hydrogen burning shell which led all models to die as red supergiants. On the
other hand, the Z=10^-4 solar metallicity models that included rotation ended
their lives as compact blue stars. Because of their extended structure, the
hydrodynamics favors more mixing and less fallback in the metal free stars than
the Z = 10^-4 models. As expected, higher energy explosions produce more
enrichment and less fallback than do lower energy explosions, and less massive
stars produce more enrichment and leave behind smaller remnants than do more
massive stars. We compare our nucleosynthetic yields to the chemical abundances
in the three most iron-poor stars yet found and reproduce the abundance pattern
of one, HE 0557-4840, with a zero metallicity 15 solar mass, 2.4 x 10^51 erg
supernova. A Salpeter IMF averaged integration of our yields for Z=0 models
with explosion energies of 2.4x10^51 ergs or less is in good agreement with the
abundances observed in larger samples of extremely metal-poor stars, provided
15 solar mass stars are included. Since the abundance patterns of extremely
metal-poor stars likely arise from a representative sample of progenitors, our
yields suggest that low-mass supernovae contributed the bulk of the metals to
the early universe.Comment: 16 pages, 11 figures; submitted to Ap
Hydrodynamic Simulation of Supernova Remnants Including Efficient Particle Acceleration
A number of supernova remnants (SNRs) show nonthermal X-rays assumed to be
synchrotron emission from shock accelerated TeV electrons. The existence of
these TeV electrons strongly suggests that the shocks in SNRs are sources of
galactic cosmic rays (CRs). In addition, there is convincing evidence from
broad-band studies of individual SNRs and elsewhere that the particle
acceleration process in SNRs can be efficient and nonlinear. If SNR shocks are
efficient particle accelerators, the production of CRs impacts the thermal
properties of the shock heated, X-ray emitting gas and the SNR evolution. We
report on a technique that couples nonlinear diffusive shock acceleration,
including the backreaction of the accelerated particles on the structure of the
forward and reverse shocks, with a hydrodynamic simulation of SNR evolution.
Compared to models which ignore CRs, the most important hydrodynamical effects
of placing a significant fraction of shock energy into CRs are larger shock
compression ratios and lower temperatures in the shocked gas. We compare our
results, which use an approximate description of the acceleration process, with
a more complete model where the full CR transport equations are solved (i.e.,
Berezhko et al., 2002), and find excellent agreement for the CR spectrum summed
over the SNR lifetime and the evolving shock compression ratio. The importance
of the coupling between particle acceleration and SNR dynamics for the
interpretation of broad-band continuum and thermal X-ray observations is
discussed.Comment: Accepted for publication in A & A; 14 pages including 11 figure
Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions
We investigate the formation and evolution of giant molecular clouds (GMCs)
in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series
of 3D adaptive mesh refinement (AMR) numerical simulations that follow both the
global evolution on scales of ~20kpc and resolve down to scales ~<10pc with a
multiphase atomic interstellar medium (ISM). In this first study, we omit star
formation and feedback, and focus on the processes of gravitational instability
and cloud collisions and interactions. We define clouds as regions with
n_H>=100cm^-3 and track the evolution of individual clouds as they orbit
through the galaxy from their birth to their eventual destruction via merger or
via destructive collision with another cloud. After ~140Myr a large fraction of
the gas in the disk has fragmented into clouds with masses ~10^6 Msun and a
mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi
steady state in which gravitational scattering of clouds keeps the disk near
the threshold of global gravitational instability. The cloud collision time is
found to be a small fraction, ~1/5, of the orbital time, and this is an
efficient mechanism to inject turbulence into the clouds. This helps to keep
clouds only moderately gravitationally bound, with virial parameters of order
unity. Many other observed GMC properties, such as mass surface density,
angular momentum, velocity dispersion, and vertical distribution, can be
accounted for in this simple model with no stellar feedback.Comment: 21 pages ApJ format, including 16 figures, accepted to Ap
Star Forming Dense Cloud Cores in the TeV {\gamma}-ray SNR RX J1713.7-3946
RX J1713.7-3946 is one of the TeV {\gamma}-ray supernova remnants (SNRs)
emitting synchrotron X rays. The SNR is associated with molecular gas located
at ~1 kpc. We made new molecular observations toward the dense cloud cores,
peaks A, C and D, in the SNR in the 12CO(J=2-1) and 13CO(J=2-1) transitions at
angular resolution of 90". The most intense core in 13CO, peak C, was also
mapped in the 12CO(J=4-3) transition at angular resolution of 38". Peak C shows
strong signs of active star formation including bipolar outflow and a
far-infrared protostellar source and has a steep gradient with a
r^{-2.20.4} variation in the average density within radius r. Peak C and
the other dense cloud cores are rim-brightened in synchrotron X rays,
suggesting that the dense cloud cores are embedded within or on the outer
boundary of the SNR shell. This confirms the earlier suggestion that the X rays
are physically associated with the molecular gas (Fukui et al. 2003). We
present a scenario where the densest molecular core, peak C, survived against
the blast wave and is now embedded within the SNR. Numerical simulations of the
shock-cloud interaction indicate that a dense clump can indeed survive shock
erosion, since shock propagation speed is stalled in the dense clump.
Additionally, the shock-cloud interaction induces turbulence and magnetic field
amplification around the dense clump that may facilitate particle acceleration
in the lower-density inter-clump space leading to the enhanced synchrotron X
rays around dense cores.Comment: 22 pages, 7 figures, to accepted in The Astrophysical Journal. A full
color version with higher resolution figures is available at
http://www.a.phys.nagoya-u.ac.jp/~sano/ApJ10/ms_sano.pd
Control of star formation by supersonic turbulence
Understanding the formation of stars in galaxies is central to much of modern
astrophysics. For several decades it has been thought that stellar birth is
primarily controlled by the interplay between gravity and magnetostatic
support, modulated by ambipolar diffusion. Recently, however, both
observational and numerical work has begun to suggest that support by
supersonic turbulence rather than magnetic fields controls star formation. In
this review we outline a new theory of star formation relying on the control by
turbulence. We demonstrate that although supersonic turbulence can provide
global support, it nevertheless produces density enhancements that allow local
collapse. Inefficient, isolated star formation is a hallmark of turbulent
support, while efficient, clustered star formation occurs in its absence. The
consequences of this theory are then explored for both local star formation and
galactic scale star formation. (ABSTRACT ABBREVIATED)Comment: Invited review for "Reviews of Modern Physics", 87 pages including 28
figures, in pres
- …