3,240 research outputs found
Stellar dust production and composition in the Magellanic Clouds
The dust reservoir in the interstellar medium of a galaxy is constantly being
replenished by dust formed in the stellar winds of evolved stars. Due to their
vicinity, nearby irregular dwarf galaxies the Magellanic Clouds provide an
opportunity to obtain a global picture of the dust production in galaxies. The
Small and Large Magellanic Clouds have been mapped with the Spitzer Space
Telescope from 3.6 to 160 {\mu}m, and these wavelengths are especially suitable
to study thermal dust emission. In addition, a large number of individual
evolved stars have been targeted for 5-40 {\mu}m spectroscopy, revealing the
mineralogy of these sources. Here I present an overview on the work done on
determining the total dust production rate in the Large and Small Magellanic
Clouds, as well as a first attempt at revealing the global composition of the
freshly produced stardust.Comment: accepted for publication by Earth, Planets & Spac
Relationship between Population Dynamics and the Self-Energy in Driven Non-Equilibrium Systems
We compare the decay rates of excited populations directly calculated within
a Keldysh formalism to the equation of motion of the population itself for a
Hubbard-Holstein model in two dimensions. While it is true that these two
approaches must give the same answer, it is common to make a number of
simplifying assumptions within the differential equation for the populations
that allows one to interpret the decay in terms of hot electrons interacting
with a phonon bath. Here we show how care must be taken to ensure an accurate
treatment of the equation of motion for the populations due to the fact that
there are identities that require cancellations of terms that naively look like
they contribute to the decay rates. In particular, the average time dependence
of the Green's functions and self-energies plays a pivotal role in determining
these decay rates.Comment: Submitted to Entrop
Identifying a forward scattering superconductor through pump-probe spectroscopy
Electron-boson scattering that is peaked in the forward direction has been
suggested as an essential ingredient for enhanced superconductivity observed in
FeSe monolayers. Here, we study the superconducting state of a system dominated
by forward scattering in the time-domain and contrast its behavior against the
standard isotropic BCS case for both s- and d-wave symmetries. An analysis of
the electron's dynamics in the pump-driven non-equilibrium state reveals that
the superconducting order in the forward-focused case is robust and persistent
against the pump-induced perturbations. The superconducting order parameter
also exhibits a non-uniform melting in momentum space. We show that this
behavior is in sharp contrast to the isotropic interaction case and propose
that time-resolved approaches are a potentially powerful tool to differentiate
the nature of the dominant coupling in correlated materials.Comment: Updated the introduction and the methods section, 6 Pages, 5 figure
General principles for the non-equilibrium relaxation of populations in quantum materials
We examine the problem of how excited populations of electrons relax after
they have been excited by a pump. We include three of the most important
relaxation processes: (i) impurity scattering; (ii) Coulomb scattering; and
(iii) electron-phonon scattering. The relaxation of an excited population of
electrons is one of the most fundamental processes measured in pump/probe
experiments, but its interpretation remains under debate. We show how several
common assumptions about non-equilibrium relaxation that are pervasive in the
field may not hold under quite general conditions. The analysis shows that
non-equilibrium relaxation is more complex than previously thought, but it
yields to recently developed theoretical methods in non-equilibrium theory. In
this work, we show how one can use many-body theory to properly interpret and
analyze these complex systems. We focus much of the discussion on implications
of these results for experiment.Comment: 13 pages, 10 figure
Determining the forsterite abundance of the dust around Asymptotic Giant Branch stars
Aims. We present a diagnostic tool to determine the abundance of the
crystalline silicate forsterite in AGB stars surrounded by a thick shell of
silicate dust. Using six infrared spectra of high mass-loss oxygen rich AGB
stars we obtain the forsterite abundance of their dust shells.
Methods. We use a monte carlo radiative transfer code to calculate infrared
spectra of dust enshrouded AGB stars. We vary the dust composition, mass-loss
rate and outer radius. We focus on the strength of the 11.3 and the 33.6 \mu m
forsterite bands, that probe the most recent (11.3 \mu m) and older (33.6 \mu
m) mass-loss history of the star. Simple diagnostic diagrams are derived,
allowing direct comparison to observed band strengths.
Results. Our analysis shows that the 11.3 \mu m forsterite band is a robust
indicator for the forsterite abundance of the current mass-loss period for AGB
stars with an optically thick dust shell. The 33.6 \mu m band of forsterite is
sensitive to changes in the density and the geometry of the emitting dust
shell, and so a less robust indicator. Applying our method to six high
mass-loss rate AGB stars shows that AGB stars can have forsterite abundances of
12% by mass and higher, which is more than the previously found maximum
abundance of 5%.Comment: Accepted for publication in A&
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