5,035 research outputs found
A one-dimensional Chandrasekhar-mass delayed-detonation model for the broad-lined Type Ia supernova 2002bo
We present 1D non-local thermodynamic equilibrium (non-LTE) time-dependent
radiative-transfer simulations of a Chandrasekhar-mass delayed-detonation model
which synthesizes 0.51 Msun of 56Ni, and confront our results to the Type Ia
supernova (SN Ia) 2002bo over the first 100 days of its evolution. Assuming
only homologous expansion, this same model reproduces the bolometric and
multi-band light curves, the secondary near-infrared (NIR) maxima, and the
optical and NIR spectra. The chemical stratification of our model qualitatively
agrees with previous inferences by Stehle et al., but reveals significant
quantitative differences for both iron-group and intermediate-mass elements. We
show that +/-0.1 Msun (i.e., +/-20 per cent) variations in 56Ni mass have a
modest impact on the bolometric and colour evolution of our model. One notable
exception is the U-band, where a larger abundance of iron-group elements
results in less opaque ejecta through ionization effects, our model with more
56Ni displaying a higher near-UV flux level. In the NIR range, such variations
in 56Ni mass affect the timing of the secondary maxima but not their magnitude,
in agreement with observational results. Moreover, the variation in the I, J,
and K_s magnitudes is less than 0.1 mag within ~10 days from bolometric
maximum, confirming the potential of NIR photometry of SNe Ia for cosmology.
Overall, the delayed-detonation mechanism in single Chandrasekhar-mass white
dwarf progenitors seems well suited for SN 2002bo and similar SNe Ia displaying
a broad Si II 6355 A line. Whatever multidimensional processes are at play
during the explosion leading to these events, they must conspire to produce an
ejecta comparable to our spherically-symmetric model.Comment: Accepted for publication in MNRAS. The hydrodynamical input and
synthetic spectra are available at https://www-n.oca.eu/supernova/home.html .
Minor changes from v1: corrected several typos and updated acknowledgement
Front speed enhancement by incompressible flows in three or higher dimensions
We study, in dimensions , the family of first integrals of an
incompressible flow: these are functions whose level surfaces are
tangent to the streamlines of the advective incompressible field. One main
motivation for this study comes from earlier results proving that the existence
of nontrivial first integrals of an incompressible flow is the main key
that leads to a "linear speed up" by a large advection of pulsating traveling
fronts solving a reaction-advection-diffusion equation in a periodic
heterogeneous framework. The family of first integrals is not well understood
in dimensions due to the randomness of the trajectories of and
this is in contrast with the case N=2. By looking at the domain of propagation
as a union of different components produced by the advective field, we provide
more information about first integrals and we give a class of incompressible
flows which exhibit `ergodic components' of positive Lebesgue measure (hence
are not shear flows) and which, under certain sharp geometric conditions, speed
up the KPP fronts linearly with respect to the large amplitude. In the proofs,
we establish a link between incompressibility, ergodicity, first integrals, and
the dimension to give a sharp condition about the asymptotic behavior of the
minimal KPP speed in terms the configuration of ergodic components.Comment: 34 pages, 3 figure
Carbon Dioxide, a Solvent and Synthon for Green Chemistry
Carbon dioxide is a renewable resource of carbon when we consider the reuse of existing CO2 as a carbon source for producing chemicals. The development of new applications is of major interest from the point of view of carbon dioxide sequestration and within the scope of green chemistry.
For example, using CO2 instead of CO or COCl2 for chemical synthesis constitutes an attractive alternative
avoiding hazardous and toxic reactants. However, it has the lowest chemical reactivity, which is a serious drawback for its transformation. Supercritical CO2 as a reaction medium offers the opportunity to replace conventional organic solvents. Its benign nature, easy handling and availability,
non volatile emitting, and the relatively low critical point (Pc = 73.8 bar, Tc = 31 °C) are particularly
interesting for catalytic applications in chemical synthesis, over a wide range of temperatures
and pressures. The benefits of coupling catalysis and supercritical fluids are both environmental
and commercial: less waste and VOCs emission, improved separation and recycling, and enhanced
productivity and selectivity.
The case study described in this paper concerns the reaction of carbon dioxide with alcohols to
afford dialkyl carbonates with special emphasis on dimethyl carbonate. It is of significant interest
because the industrial production of this class of compounds, including polycarbonates, carbamates,
and polyurethanes, involves phosgene with strong concerns on environmental impact, transport, safety and waste elimination. The future of carbon dioxide in green chemistry, including supercritical applications, is highly linked to the development of basic knowledge, know-how, and
tools for the design of catalyst precursors and reactors
Interaction Quench in Nonequilibrium Luttinger Liquids
We study the relaxation dynamics of a nonequilibrium Luttinger liquid after a
sudden interaction switch-on ("quench"), focussing on a double-step initial
momentum distribution function. In the framework of the non-equilibrium
bosonization, the results are obtained in terms of singular Fredholm
determinants that are evaluated numerically and whose asymptotics are found
analytically. While the quasi-particle weights decay exponentially with time
after the quench, this is not a relaxation into a thermal state, in view of the
integrability of the model. The steady-state distribution emerging at infinite
times retains two edges which support Luttinger-liquid-like power-law
singularities smeared by dephasing. The obtained critical exponents and the
dephasing length are found to depend on the initial nonequilibrium state.Comment: 11 pages, 5 figure
Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation
The faster light-curve evolution of low-luminosity Type Ia supernovae (SNe
Ia) suggests that they could result from the explosion of white dwarf (WD)
progenitors below the Chandrasekhar mass (). Here we present 1D
non-LTE time-dependent radiative transfer simulations of pure central
detonations of carbon-oxygen WDs with a mass (M_\rm{tot}) between 0.88
M and 1.15 M, and a yield between 0.08
M and 0.84 M. Their lower ejecta density compared to
models results in a more rapid increase of the luminosity at early
times and an enhanced -ray escape fraction past maximum light.
Consequently, their bolometric light curves display shorter rise times and
larger post-maximum decline rates. Moreover, the higher
M(^{56}\rm{Ni})/M_\rm{tot} ratio at a given mass enhances the
temperature and ionization level in the spectrum-formation region for the less
luminous models, giving rise to bluer colours at maximum light and a faster
post-maximum evolution of the colour. For sub- models fainter
than mag at peak, the greater bolometric decline and faster
colour evolution lead to a larger -band post-maximum decline rate, . In particular, all of our previously-published models
(standard and pulsational delayed detonations) are confined to mag, while the sub- models with
M_\rm{tot}\lesssim 1 M extend beyond this limit to mag for a peak mag, in better agreement
with the observed width-luminosity relation (WLR). Regardless of the precise
ignition mechanism, these simulations suggest that fast-declining SNe Ia at the
faint end of the WLR could result from the explosion of WDs whose mass is
significantly below the Chandrasekhar limit.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
The Geodetic Hull Number is Hard for Chordal Graphs
We show the hardness of the geodetic hull number for chordal graphs
Radiative Properties of Pair-instability Supernova Explosions
We present non-LTE time-dependent radiative-transfer simulations of
pair-instability supernovae (PISNe) stemming from red-supergiant (RSG),
blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born
in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties
in convection and stellar mass-loss rates, our initial conditions come from
physically-consistent models that treat evolution from the main-sequence, the
onset of the pair-production instability, and the explosion phase. With our set
of input models characterized by large 56Ni and ejecta masses, and large
kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar,
and Ib/c light-curve morphologies, although they have larger peak bolometric
luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss
the spectral properties for each model during the photospheric and nebular
phases, including Balmer lines in II-P and II-pec at early times, the dominance
of lines from intermediate-mass-elements (IMEs) near the bolometric maximum,
and the strengthening of metal line blanketing thereafter. Having similar
He-core properties, all models exhibit similar post-peak spectra that are
strongly blanketed by FeII and FeI lines, characterized by red colors, and that
arise from photospheres/ejecta with a temperature of <4000K. Combined with the
modest line widths after bolometric peak, these properties contrast with those
of known super-luminous SNe suggesting that PISNe are yet to be discovered.
Being reddish, PISNe will be difficult to observe at high redshift except when
they stem from RSG explosions, in which case they could be used as metallicity
probes and distance indicators.Comment: accepted to MNRA
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