1,280 research outputs found
A semi-analytical light curve model and its application to type IIP supernovae
The aim of this work is to present a semi-analytical light curve modeling
code which can be used for estimating physical properties of core collapse
supernovae (SNe) in a quick and efficient way. To verify our code we fit light
curves of Type II SNe and compare our best parameter estimates to those from
hydrodynamical calculations. For this analysis we use the quasi-bolometric
light curves of five different Type IIP supernovae. In each case we get
appropriate results for the initial pre-supernova parameters. We conclude that
this semi-analytical light curve model is useful to get approximate physical
properties of Type II SNe without using time-consuming numerical hydrodynamic
simulations.Comment: accepted for publication in Astronomy \& Astrophysics; corrected
Fig.2, 3,
A Comprehensive Dust Model Applied to the Resolved Beta Pictoris Debris Disk from Optical to Radio Wavelengths
We investigate whether varying the dust composition (described by the optical
constants) can solve a persistent problem in debris disk modeling--the
inability to fit the thermal emission without over-predicting the scattered
light. We model five images of the beta Pictoris disk: two in scattered light
from HST/STIS at 0.58 microns and HST/WFC3 at 1.16 microns, and three in
thermal emission from Spitzer/MIPS at 24 microns, Herschel/PACS at 70 microns,
and ALMA at 870 microns. The WFC3 and MIPS data are published here for the
first time. We focus our modeling on the outer part of this disk, consisting of
a parent body ring and a halo of small grains. First, we confirm that a model
using astronomical silicates cannot simultaneously fit the thermal and
scattered light data. Next, we use a simple, generic function for the optical
constants to show that varying the dust composition can improve the fit
substantially. Finally, we model the dust as a mixture of the most plausible
debris constituents: astronomical silicates, water ice, organic refractory
material, and vacuum. We achieve a good fit to all datasets with grains
composed predominantly of silicates and organics, while ice and vacuum are, at
most, present in small amounts. This composition is similar to one derived from
previous work on the HR 4796A disk. Our model also fits the thermal SED,
scattered light colors, and high-resolution mid-IR data from T-ReCS for this
disk. Additionally, we show that sub-blowout grains are a necessary component
of the halo.Comment: 23 pages, 20 figures, accepted to Ap
Shining new light on the multifaceted dissociative photoionisation dynamics of CCl<sub>4</sub>
Statisticality restored: high internal energy CCl4+ dissociates mostly according to statistical theory, and an intersystem crossing path precludes fluorescence.</p
Environmental Harshness and Fitness Improving Innovations
Fitness improving innovations occur in populations of organisms as genetic changes (mutations) that allow better fit with the environmental niche of the organisms. Similarly, fitness improving innovations may occur in the context of human communities as well in terms of socio-economic innovations (e.g. new ways of organizing the military, new products or services) that lead to more efficient use of available resources. Here we explore the link between such innovations and the harshness of the environment, where the populations live. Environmental harshness characterizes the availability of population growth supporting resources in the environment. Our analysis shows that if the harshness of the environment varies smoothly with the distance, the expected extent of fitness improving innovations and of the resource utilization efficiency of populations depends in a combined linear and harmonic manner on the harshness of the environment at the location of origin of the populations. We explore the implications of this result for particular cases of both biological and social environments (e.g. gene drives, business innovation)
Long-Term Evolution of Massive Black Hole Binaries. III. Binary Evolution in Collisional Nuclei
[Abridged] In galactic nuclei with sufficiently short relaxation times,
binary supermassive black holes can evolve beyond their stalling radii via
continued interaction with stars. We study this "collisional" evolutionary
regime using both fully self-consistent N-body integrations and approximate
Fokker-Planck models. The N-body integrations employ particle numbers up to
0.26M and a direct-summation potential solver; close interactions involving the
binary are treated using a new implementation of the Mikkola-Aarseth chain
regularization algorithm. Even at these large values of N, two-body scattering
occurs at high enough rates in the simulations that they can not be simply
scaled to the large-N regime of real galaxies. The Fokker-Planck model is used
to bridge this gap; it includes, for the first time, binary-induced changes in
the stellar density and potential. The Fokker-Planck model is shown to
accurately reproduce the results of the N-body integrations, and is then
extended to the much larger N regime of real galaxies. Analytic expressions are
derived that accurately reproduce the time dependence of the binary semi-major
axis as predicted by the Fokker-Planck model. Gravitational wave coalescence is
shown to occur in <10 Gyr in nuclei with velocity dispersions below about 80
km/s. Formation of a core results from a competition between ejection of stars
by the binary and re-supply of depleted orbits via two-body scattering. Mass
deficits as large as ~4 times the binary mass are produced before coalescence.
After the two black holes coalesce, a Bahcall-Wolf cusp appears around the
single hole in one relaxation time, resulting in a nuclear density profile
consisting of a flat core with an inner, compact cluster, similar to what is
observed at the centers of low-luminosity spheroids.Comment: 21 page
The HR 4796A Debris System: Discovery of Extensive Exo-Ring Dust Material
The optically and IR bright, and starlight-scattering, HR 4796A ring-like
debris disk is one of the most (and best) studied exoplanetary debris systems.
The presence of a yet-undetected planet has been inferred (or suggested) from
the narrow width and inner/outer truncation radii of its r = 1.05" (77 au)
debris ring. We present new, highly sensitive, Hubble Space Telescope (HST)
visible-light images of the HR 4796A circumstellar debris system and its
environment over a very wide range of stellocentric angles from 0.32" (23 au)
to ~ 15" (1100 au). These very high contrast images were obtained with the
Space Telescope Imaging Spectrograph (STIS) using 6-roll PSF-template
subtracted coronagraphy suppressing the primary light of HR 4796A and using
three image plane occulters and simultaneously subtracting the background light
from its close angular proximity M2.5V companion. The resulting images
unambiguously reveal the debris ring embedded within a much larger,
morphologically complex, and bi-axially asymmetric exoring scattering
structure. These images at visible wavelengths are sensitive to, and map, the
spatial distribution, brightness, and radial surface density of micron size
particles over 5 dex in surface brightness. These particles in the exo-ring
environment may be unbound from the system and interacting with the local ISM.
Herein we present a new morphological and photometric view of the larger than
prior seen HR 4796A exoplanetary debris system with sensitivity to small
particles at stellocentric distances an order of magnitude greater than has
previously been observed.Comment: 28 pages, 17 figures, accepted for publication in the Astronomical
Journal 21 December 201
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