6,666 research outputs found
Detailed Spectral Modeling of a 3-D Pulsating Reverse Detonation Model: Too Much Nickel
We calculate detailed NLTE synthetic spectra of a Pulsating Reverse
Detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae.
While the hydro models are calculated in 3-D, the spectra use an angle averaged
hydro model and thus some of the 3-D details are lost, but the overall average
should be a good representation of the average observed spectra. We study the
model at 3 epochs: maximum light, seven days prior to maximum light, and 5 days
after maximum light. At maximum the defining Si II feature is prominent, but
there is also a prominent C II feature, not usually observed in normal SNe Ia
near maximum. We compare to the early spectrum of SN 2006D which did show a
prominent C II feature, but the fit to the observations is not compelling.
Finally we compare to the post-maximum UV+optical spectrum of SN 1992A. With
the broad spectral coverage it is clear that the iron-peak elements on the
outside of the model push too much flux to the red and thus the particular PRD
realizations studied would be intrinsically far redder than observed SNe Ia. We
briefly discuss variations that could improve future PRD models.Comment: 15 pages, 4 figures, submitted to Ap
The Joint Efficient Dark-energy Investigation (JEDI): Measuring the cosmic expansion history from type Ia supernovae
JEDI (Joint Efficient Dark-energy Investigation) is a candidate
implementation of the NASA-DOE Joint Dark Energy Mission (JDEM). JEDI will
probe dark energy in three independent methods: (1) type Ia supernovae, (2)
baryon acoustic oscillations, and (3) weak gravitational lensing. In an
accompanying paper, an overall summary of the JEDI mission is given. In this
paper, we present further details of the supernova component of JEDI. To derive
model-independent constraints on dark energy, it is important to precisely
measure the cosmic expansion history, H(z), in continuous redshift bins from z
\~ 0-2 (the redshift range in which dark energy is important). SNe Ia at z > 1
are not readily accessible from the ground because the bulk of their light has
shifted into the near-infrared where the sky background is overwhelming; hence
a space mission is required to probe dark energy using SNe. Because of its
unique near-infrared wavelength coverage (0.8-4.2 microns), JEDI has the
advantage of observing SNe Ia in the rest frame J band for the entire redshift
range of 0 < z < 2, where they are less affected by dust, and appear to be
nearly perfect standard candles. During the first year of JEDI operations,
spectra and light curves will be obtained for ~4,000 SNe Ia at z < 2. The
resulting constraints on dark energy are discussed, with special emphasis on
the improved precision afforded by the rest frame near-infrared data.Comment: 8 pages, accepted for publication in SPIE proceeding
Can Music Increase Empathy? Interpreting Musical Experience Through the EmpathizingâSystemizing (E-S) Theory: Implications for Autism
Recent research has provided evidence that musical interaction can promote empathy. Yet little is known about the underlying intrapersonal and social psychological processes that are involved when this occurs. For example, which types of music increase empathy and which types decrease it; what role, if any, does empathy play in determining individual differences in musical preference, perception, and performance; or, how do these psychological underpinnings help explain the musical experiences of people with autism spectrum conditions (ASC). To address these questions we employ the EmpathizingâSystemizing (E-S) theory as a fruitful framework in which to understand these music-related phenomena. Specifically, we explore how individual differences in musical preference, perception, and performance can be explained by E-S theory. We provide examples from open-ended descriptions of strong musical experiences to demonstrate the ways in which empathy and music inter-relate. Importantly, we discuss the implications for the study of autism, and for how music therapists and clinicians can use music as a tool in their work with individuals diagnosed with ASC.
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A novel hypothesis of dinosaur relationships and early dinosaur evolution
For nearly 130 years dinosaurs have been divided into two distinct clades Ornithischia and Saurischia. Here, we present a radical new hypothesis for the phylogenetic relationships of the major dinosaurian groups, one that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study recovers, for the first time, a sister-group relationship between Ornithischia and Theropoda (Ornithoscelida), with Sauropodomorpha + Herrerasauridae forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests the independent acquisition of hypercarnivory in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as striking convergences between theropods and early ornithischians
Analytic Inversion of Emission Lines of Arbitrary Optical Depth for the Structure of Supernova Ejecta
We derive a method for inverting emission line profiles formed in supernova
ejecta. The derivation assumes spherical symmetry and homologous expansion
(i.e., ), is analytic, and even takes account of occultation by
a pseudo-photosphere. Previous inversion methods have been developed which are
restricted to optically thin lines, but the particular case of homologous
expansion permits an analytic result for lines of {\it arbitrary} optical
depth. In fact, we show that the quantity that is generically retrieved is the
run of line intensity with radius in the ejecta. This result is
quite general, and so could be applied to resonance lines, recombination lines,
etc. As a specific example, we show how to derive the run of (Sobolev) optical
depth with radius in the case of a pure resonance scattering
emission line.Comment: 6 pages, no figures, to appear in Astrophysical Journal Letters,
requires aaspp4.sty to late
The NextGen Model Atmosphere grid: II. Spherically symmetric model atmospheres for giant stars with effective temperatures between 3000 and 6800~K
We present the extension of our NextGen model atmosphere grid to the regime
of giant stars. The input physics of the models presented here is nearly
identical to the NextGen dwarf atmosphere models, however spherical geometry is
used self-consistently in the model calculations (including the radiative
transfer). We re-visit the discussion of the effects of spherical geometry on
the structure of the atmospheres and the emitted spectra and discuss the
results of NLTE calculations for a few selected models.Comment: ApJ, in press (November 1999), 13 pages, also available at
http://dilbert.physast.uga.edu/~yeti/PAPERS and at
ftp://calvin.physast.uga.edu/pub/preprints/NG-giants.ps.g
Controlling Formal Fibers of Countably Many Principal Prime Ideals
Let be a complete local (Noetherian) ring. For each ,
let be a nonempty countable set of nonmaximal pairwise incomparable prime
ideals of , and suppose that if , then either or no
element of is contained in an element of . We provide necessary and
sufficient conditions for to be the completion of a local integral domain
satisfying the condition that, for all , there is a
nonzero prime element of , such that is exactly the set of
maximal elements of the formal fiber of at . We then prove related
results where the domain is required to be countable and/or excellent.Comment: 29 page
Comparative Direct Analysis of Type Ia Supernova Spectra. IV. Postmaximum
A comparative study of optical spectra of Type Ia supernovae (SNe Ia)
obtained near 1 week, 3 weeks, and 3 months after maximum light is presented.
Most members of the four groups that were defined on the basis of maximum light
spectra in Paper II (core normal, broad line, cool, and shallow silicon)
develop highly homogeneous postmaximum spectra, although there are interesting
exceptions. Comparisons with SYNOW synthetic spectra show that most of the
spectral features can be accounted for in a plausible way. The fits show that 3
months after maximum light, when SN Ia spectra are often said to be in the
nebular phase and to consist of forbidden emission lines, the spectra actually
remain dominated by resonance scattering features of permitted lines, primarily
those of Fe II. Even in SN 1991bg, which is said to have made a very early
transition to the nebular phase, there is no need to appeal to forbidden lines
at 3 weeks postmaximum, and at 3 months postmaximum the only clear
identification of a forbidden line is [Ca II] 7291, 7324. Recent studies of SN
Ia rates indicate that most of the SNe Ia that have ever occurred have been
"prompt" SNe Ia, produced by young (100,000,000 yr) stellar populations, while
most of the SNe Ia that occur at low redshift today are "tardy", produced by an
older (several Gyrs) population. We suggest that the shallow silicon SNe Ia
tend to be the prompt ones.Comment: Accepted by PAS
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