3,066 research outputs found
Constraints on supernova progenitors from spatial correlations with H-alpha emission
We have attempted to constrain the progenitors of all supernova types,
through correlations of the positions of historical supernovae with recent star
formation, as traced by H-alpha emission. Through pixel statistics we have
found that a large fraction of the SNII population do not show any association
with current star formation, which we put down to a 'runaway' fraction of these
progenitors. The SNIb/c population accurately traces the H-alpha emission, with
some suggestion that the SNIc progenitors show a higher degree of correlation
than the SNIb, suggesting higher mass progenitors for the former. Overall the
SNIa population only show a weak correlation to the positions of HII regions,
but as many as a half may be associated with a young stellar population.Comment: To appear in conference proceedings: "Supernova 1987A: 20 Years After
-- Supernovae & Gamma-Ray Bursters", held in Aspen, February 200
Ultimate decoherence border for matter-wave interferometry
Stochastic backgrounds of gravitational waves are intrinsic fluctuations of
spacetime which lead to an unavoidable decoherence mechanism. This mechanism
manifests itself as a degradation of the contrast of quantum interferences. It
defines an ultimate decoherence border for matter-wave interferometry using
larger and larger molecules. We give a quantitative characterization of this
border in terms of figures involving the gravitational environment as well as
the sensitivity of the interferometer to gravitational waves. The known level
of gravitational noise determines the maximal size of the molecular probe for
which interferences may remain observable. We discuss the relevance of this
result in the context of ongoing progresses towards more and more sensitive
matter-wave interferometry.Comment: 4 page
Aspects of quantum coherence in the optical Bloch equations
Aspects of coherence and decoherence are analyzed within the optical Bloch
equations. By rewriting the analytic solution in an alternate form, we are able
to emphasize a number of unusual features: (a) despite the Markovian nature of
the bath, coherence at long times can be retained; (b) the long-time asymptotic
degree of coherence in the system is intertwined with the asymptotic difference
in level populations; (c) the traditional population-relaxation and decoherence
times, and , lose their meaning when the system is in the presence
of an external field, and are replaced by more general overall timescales; (d)
increasing the field strength, quantified by the Rabi frequency, ,
increases the rate of decoherence rather than reducing it, as one might expect;
and (e) maximum asymptotic coherence is reached when the system parameters
satisfy .Comment: 18 pages, 6 figures; to appear in J Chem Phy
The Archean crust in the Wawa-Chapleau-Timmins region. A field guidebook prepared for the 1983 Archean Geochemistry-Early Crustal Genesis Field Conference
This guidebook describes the characteristics and interrelationships of Archean greenstone-granite and high-grade gneiss terrains of the Superior Province. A 300-km long west to east transect between Wawa and Timmins, Ontario will be used to illustrate regional-scale relationships. The major geological features of the Superior Province are described
Quantum noise and stochastic reduction
In standard nonrelativistic quantum mechanics the expectation of the energy
is a conserved quantity. It is possible to extend the dynamical law associated
with the evolution of a quantum state consistently to include a nonlinear
stochastic component, while respecting the conservation law. According to the
dynamics thus obtained, referred to as the energy-based stochastic Schrodinger
equation, an arbitrary initial state collapses spontaneously to one of the
energy eigenstates, thus describing the phenomenon of quantum state reduction.
In this article, two such models are investigated: one that achieves state
reduction in infinite time, and the other in finite time. The properties of the
associated energy expectation process and the energy variance process are
worked out in detail. By use of a novel application of a nonlinear filtering
method, closed-form solutions--algebraic in character and involving no
integration--are obtained for both these models. In each case, the solution is
expressed in terms of a random variable representing the terminal energy of the
system, and an independent noise process. With these solutions at hand it is
possible to simulate explicitly the dynamics of the quantum states of
complicated physical systems.Comment: 50 page
Stellar population constraints on the ages of galactic bars
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. We present a study of the stellar populations within the central regions of four nearby barred galaxies, and use a novel technique to constrain the duration of bar activity. We focus on the star formation 'desert', a region within each of these galaxies where star formation appears to have been suppressed by the bar. New Hß spectroscopic data are presented, and used to produce spectroscopic line indices which are compared with theoretical predictions from population synthesis models for simple stellar populations and temporally truncated star formation histories. This analysis shows that the dearth of star formation activity in these regions appears to have been continuing for at least 1 Gyr, with time-scales of several Gyr indicated for two of the galaxies. This favours models in which strong bars can be long-lived features of galaxies, but our results also indicate a significant diversity in stellar population ages, and hence in the implied histories of bar activity in these four galaxies
Chemical abundance anticorrelations in globular cluster stars: The effect on cluster integrated spectra
It is widely accepted that individual Galactic globular clusters harbor two
coeval generations of stars, the first one born with the `standard'
-enhanced metal mixture observed in field Halo objects, the second one
characterized by an anticorrelated CN-ONa abundance pattern overimposed on the
first generation, -enhanced metal mixture. We have investigated with
appropriate stellar population synthesis models how this second generation of
stars affects the integrated spectrum of a typical metal rich Galactic globular
cluster, like 47\,Tuc, focusing our analysis on the widely used Lick-type
indices. We find that the only indices appreciably affected by the abundance
anticorrelations are Ca4227, G4300, , and NaD. The
age-sensitive Balmer line, Fe line and the [MgFe] indices widely used to
determine age, Fe and total metallicity of extragalactic systems are largely
insensitive to the second generation population. Enhanced He in second
generation stars affects also the Balmer line indices of the integrated
spectra, through the change of the turn off temperature and -- in the
assumption that the mass loss history of both stellar generations is the same
-- the horizontal branch morphology of the underlying isochrones.Comment: Accepted for publication in Ap
Decoherent Neutrino Mixing, Dark Energy and Matter-Antimatter Asymmetry
A CPT violating decoherence scenario can easily account for all the
experimental evidence in the neutrino sector including LSND. In this work it is
argued that this framework can also accommodate the Dark Energy content of the
Universe, as well as the observed matter-antimatter asymmetry.Comment: 6 pages, no figures, some typos corrected, and discussion modified
below eq (3), no effects on conclusion
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