14,344 research outputs found
An Advanced, Three-Dimensional Plotting Library for Astronomy
We present a new, three-dimensional (3D) plotting library with advanced
features, and support for standard and enhanced display devices. The library -
S2PLOT - is written in C and can be used by C, C++ and FORTRAN programs on
GNU/Linux and Apple/OSX systems. S2PLOT draws objects in a 3D (x,y,z) Cartesian
space and the user interactively controls how this space is rendered at run
time. With a PGPLOT inspired interface, S2PLOT provides astronomers with
elegant techniques for displaying and exploring 3D data sets directly from
their program code, and the potential to use stereoscopic and dome display
devices. The S2PLOT architecture supports dynamic geometry and can be used to
plot time-evolving data sets, such as might be produced by simulation codes. In
this paper, we introduce S2PLOT to the astronomical community, describe its
potential applications, and present some example uses of the library.Comment: 12 pages, 10 eps figures (higher resolution versions available from
http://astronomy.swin.edu.au/s2plot/paperfigures). The S2PLOT library is
available for download from http://astronomy.swin.edu.au/s2plo
Ejection of Supernova-Enriched Gas From Dwarf Disk Galaxies
We examine the efficiency with which supernova-enriched gas may be ejected
from dwarf disk galaxies, using a methodology previously employed to study the
self-enrichment efficiency of dwarf spheroidal systems. Unlike previous studies
that focused on highly concentrated starbursts, in the current work we consider
discrete supernova events spread throughout various fractions of the disk. We
model disk systems having gas masses of 10^8 and 10^9 solar masses with
supernova rates of 30, 300, and 3000 per Myr. The supernova events are confined
to the midplane of the disk, but distributed over radii of 0, 30, and 80% of
the disk radius, consistent with expectations for Type II supernovae. In
agreement with earlier studies, we find that the enriched material from
supernovae is largely lost when the supernovae are concentrated near the
nucleus, as expected for a starburst event. In contrast, however, we find the
loss of enriched material to be much less efficient when the supernovae occur
over even a relatively small fraction of the disk. The difference is due to the
ability of the system to relax following supernova events that occur over more
extended regions. Larger physical separations also reduce the likelihood of
supernovae going off within low-density "chimneys" swept out by previous
supernovae. We also find that, for the most distributed systems, significant
metal loss is more likely to be accompanied by significant mass loss. A
comparison with theoretical predications indicates that, when undergoing
self-regulated star formation, galaxies in the mass range considered shall
efficiently retain the products of Type II supernovae.Comment: 16 pages, 14 figures, to appear in Astrophysical Journal; higher
resolution figures available through Ap
Zero-bias Anomaly of Tunneling into the Edge of a 2D Electron System
We investigate the electron tunneling into the edge of a clean weakly
interacting two-dimensional electron gas. It is shown that the corresponding
differential conductance has a cusp at zero bias, and is characterized
by a universal slope at . This singularity originates from the
electron scattering on the Friedel oscillation caused by the boundary of the
system.Comment: 10 pages, uuencoded compressed Postscript file, to appear in Phys.
Rev. B (Rapid Communications
Roche Lobe Overflow from Dwarf Stellar Systems
We use both analytical analyses and numerical simulations to examine the
evolution of residual gas within tidally-limited dwarf galaxies and globular
clusters. If the gas sound speed exceeds about 10% of the central velocity
dispersion, as is the case for ionized gas within small stellar systems, the
gas shall have significant density at the tidal radius, and the gas may be lost
on timescales as short as a few times the sound crossing time of the system. In
colder systems, the density at the tidal radius is much lower, greatly reducing
the mass loss rate, and the system may retain its gas for a Hubble time. The
tidally removed gas shall follow an orbit close to that of the original host
system, forming an extended stream of ionized, gaseous debris. Tidal mass loss
severely limits the ability of dwarf systems to continuously form stars. The
ordinary gas content in many dwarf galaxies is fully ionized during high
red-shift epochs, possibly preventing star formation in some systems, leading
to the formation of starless, dark-matter concentrations. In either the field
or in the center of galaxy clusters, ionized gas may be retained by dwarf
galaxies, even though its sound speed may be comparable to or even exceed the
velocity dispersion. These processes may help to explain some observed
differences among dwarf galaxy types, as well as observations of the haloes of
massive galaxies.Comment: 28 pages, LaTeX, AASTex macro
Poly[[tetrakis(μ2-pyrazine N,N′-dioxide-κ2 O:O′)erbium(III)] tris(perchlorate)]
The title three-dimensional coordination network, {[Er(C4H4N2O2)4](ClO4)3}n, is isostructural to that of other lanthanides. The Er+3 cation lies on a fourfold roto-inversion axis. It is coordinated in a distorted square-antiprismatic fashion by eight O atoms from bridging pyrazine N,N′-dioxide ligands. There are two unique pyrazine N,N′-dioxide ligands. One ring is located around an inversion center, and there is a a twofold rotation axis at the center of the other ring. There are also two unique perchlorate anions. One is centered on a twofold rotation axis and the other on a fourfold roto-inversion axis. The perchlorate anions are located in channels that run perpendicular to (001) and (110) and interact with the coordination network through C—H⋯O hydrogen bonds
Dark Matter Substructure in Galactic Halos
We use numerical simulations to examine the substructure within galactic and
cluster mass halos that form within a hierarchical universe. Clusters are
easily reproduced with a steep mass spectrum of thousands of substructure
clumps that closely matches observations. However, the survival of dark matter
substructure also occurs on galactic scales, leading to the remarkable result
that galaxy halos appear as scaled versions of galaxy clusters. The model
predicts that the virialised extent of the Milky Way's halo should contain
about 500 satellites with circular velocities larger than Draco and Ursa-Minor
i.e. bound masses > 10^8Mo and tidally limited sizes > kpc. The substructure
clumps are on orbits that take a large fraction of them through the stellar
disk leading to significant resonant and impulsive heating. Their abundance and
singular density profiles has important implications for the existence of old
thin disks, cold stellar streams, gravitational lensing and indirect/direct
detection experiments.Comment: Astrophysical Journal Letters. 4 pages, latex. Simulation images and
movies at http://star-www.dur.ac.uk:80/~moore
Density profiles and substructure of dark matter halos: converging results at ultra-high numerical resolution
Can N-body simulations reliably determine the structural properties of dark
matter halos? Focussing on a Virgo-sized galaxy cluster, we increase the
resolution of current ``high resolution simulations'' by almost an order of
magnitude to examine the convergence of the important physical quantities. We
have 4 million particles within the cluster and force resolution 0.5 kpc/h
(0.05% of the virial radius). The central density profile has a logarithmic
slope of -1.5, as found in lower resolution studies of the same halo,
indicating that the profile has converged to the ``physical'' limit down to
scales of a few kpc. Also the abundance of substructure is consistent with that
derived from lower resolution runs; on the scales explored, the mass and
circular velocity functions are close to power laws of exponents ~ -1.9 and -4.
Overmerging appears to be globally unimportant for suhalos with circular
velocities > 100 km/s. We can trace most of the cluster progenitors from z=3 to
the present; the central object (the dark matter analog of a cD galaxy)is
assembled between z=3 and 1 from the merging of a dozen halos with v_circ \sim
300 km/s. The mean circular velocity of the subhalos decreases by ~ 20% over 5
billion years, due to tidal mass loss. The velocity dispersions of halos and
dark matter globally agree within 10%, but the halos are spatially anti-biased,
and, in the very central region of the cluster, they show positive velocity
bias; however, this effect appears to depend on numerical resolution.Comment: 19 pages, 13 figures, ApJ, in press. Text significantly clarifie
Axiomatic approach to radiation reaction of scalar point particles in curved spacetime
Several different methods have recently been proposed for calculating the
motion of a point particle coupled to a linearized gravitational field on a
curved background. These proposals are motivated by the hope that the point
particle system will accurately model certain astrophysical systems which are
promising candidates for observation by the new generation of gravitational
wave detectors. Because of its mathematical simplicity, the analogous system
consisting of a point particle coupled to a scalar field provides a useful
context in which to investigate these proposed methods. In this paper, we
generalize the axiomatic approach of Quinn and Wald in order to produce a
general expression for the self force on a point particle coupled to a scalar
field following an arbitrary trajectory on a curved background. Our equation
includes the leading order effects of the particle's own fields, commonly
referred to as ``self force'' or ``radiation reaction'' effects. We then
explore the equations of motion which follow from this expression in the
absence of non-scalar forces.Comment: 17 pages, 1 figur
HAT-P-26b: A Low-Density Neptune-Mass Planet Transiting a K Star
We report the discovery of HAT-P-26b, a transiting extrasolar planet orbiting
the moderately bright V=11.744 K1 dwarf star GSC 0320-01027, with a period P =
4.234516 +- 0.000015 d, transit epoch Tc = 2455304.65122 +- 0.00035 (BJD), and
transit duration 0.1023 +- 0.0010 d. The host star has a mass of 0.82 +- 0.03
Msun, radius of 0.79 + 0.10 - 0.04 Rsun, effective temperature 5079 +- 88 K,
and metallicity [Fe/H] = -0.04 +- 0.08. The planetary companion has a mass of
0.059 +- 0.007 MJ, and radius of 0.565 + 0.072 - 0.032 RJ yielding a mean
density of 0.40 +- 0.10 g cm-3. HAT-P-26b is the fourth Neptune-mass transiting
planet discovered to date. It has a mass that is comparable to those of Neptune
and Uranus, and slightly smaller than those of the other transiting
Super-Neptunes, but a radius that is ~65% larger than those of Neptune and
Uranus, and also larger than those of the other transiting Super-Neptunes.
HAT-P-26b is consistent with theoretical models of an irradiated Neptune-mass
planet with a 10 Mearth heavy element core that comprises >~ 50% of its mass
with the remainder contained in a significant hydrogen-helium envelope, though
the exact composition is uncertain as there are significant differences between
various theoretical models at the Neptune-mass regime. The equatorial
declination of the star makes it easily accessible to both Northern and
Southern ground-based facilities for follow-up observations.Comment: 16 pages, 9 figures, 5 tables, submitted to Ap
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