7,129 research outputs found
Evolution of the ISM of Starburst galaxies: the SN heating efficiency
The interstellar medium heated by SN explosions may acquire an expansion
velocity larger than the escape velocity and leave the galaxy through a
supersonic wind. SN ejecta are transported out of the galaxies by such winds
which thus affect the chemical evolution of the galaxies. The effectiveness of
the processes mentioned above depends on the heating efficiency (HE) of the
SNe, that is a matter of debate. We have constructed a simple semi-analytic
model, considering the essential ingredients of a SB environment which is able
to qualitatively trace the thermalisation history of the ISM in a SB region and
determine the HE evolution. We find that, as long as the mass-loss rate of the
clouds remains larger than the rate at which the SNRs interact one with each
other, the SN heating efficiency remains very small, as radiative cooling of
the gas dominates. We conclude that the HE value has a time-dependent trend
that is sensitive to the initial conditions of the system.Comment: 17 pages, 18 figures, A&A accepte
Studying a dual-species BEC with tunable interactions
We report on the observation of controllable spatial separation in a
dual-species Bose-Einstein condensate (BEC) with Rb and Rb.
Interparticle interactions between the different components can change the
miscibility of the two quantum fluids. In our experiments, we clearly observe
the immiscible nature of the two simultaneously Bose-condensed species via
their spatial separation. Furthermore the Rb Feshbach resonance near 155
G is used to change them between miscible and immiscible by tuning the
Rb scattering length. Our apparatus is also able to create Rb
condensates with up to atoms which represents a significant
improvement over previous work
Multidimensional Hydrodynamical Simulations of radiative cooling SNRs-clouds interactions: an application to Starburst Environments
In this work we are interested to study the by-products of SNR-clouds in a
starburst (SB) system. These interactions can have an important role in the
recycling of matter from the clouds to the ISM and vice-versa. In the present
work, we have focused our attention on the global effects of the interactions
between clouds and SN shock waves in the ISM of SB environments, and performed
3-D radiative cooling hydrodynamical simulations with the adaptive YGUAZU grid
code. We have also considered the effects of the photo-evaporation due to the
presence of a high number of UV photons from hot stars and supernovae (SNe).
The results have shown that, in the presence of radiative cooling, instead of
an efficient gas mixing with the diffuse ISM, the interactions cause the
fragmentation of the clouds into smaller ones. The results have also revealed
that the SNR-clouds interactions are less efficient at producing substantial
mass loss from the clouds to the diffuse ISM than mechanisms such as the
photo-evaporation caused by the UV flux from the hot stars.Comment: 15 pages, 25 figures. Figures with higher resolution at the page:
http://www.astro.iag.usp.br/~dalpino/ Astronomy & Astrophysics accepte
CHAINS OF STABILITY: BUILDING FINANCIAL AND CULTURAL COMMUNITY SUSTAINABILITY FOR LATINAS IN RICHMOND & CHESTERFIELD, VIRGINIA
As the Latinx population in the US continues to grow, new Latin-centric ethnic enclaves are developing in urban areas, including those in US southern states. While there has been some discourse on the role of Latin immigrants in the US labor market generally, there is limited literature addressing the specific experiences of Latinas as inhabitants of urban spaces and the factors impacting their economic sustainability. Latinas, on average, earn 1.00 a white male earns. Their economic position, combined with their cultural traditions and practices, raises questions about how they achieve economic security in the US. This research uses Richmond and Chesterfield, Virginia as a case study to further explore the internal and external factors that positively and negatively impact Latinas\u27 economic well-being and how these translate into various forms of cultural capital. Based on the findings, I offer three key recommendations for planners to better support Latinasâ in Richmond and Chesterfield, Virginia
Mapping the structural diversity of C60 carbon clusters and their infrared spectra
The current debate about the nature of the carbonaceous material carrying the
infrared (IR) emission spectra of planetary and proto-planetary nebulae,
including the broad plateaus, calls for further studies on the interplay
between structure and spectroscopy of carbon-based compounds of astrophysical
interest. The recent observation of C60 buckminsterfullerene in space suggests
that carbon clusters of similar size may also be relevant. In the present work,
broad statistical samples of C60 isomers were computationally determined
without any bias using a reactive force field, their IR spectra being
subsequently obtained following local optimization with the
density-functional-based tight-binding theory. Structural analysis reveals four
main structural families identified as cages, planar polycyclic aromatics,
pretzels, and branched. Comparison with available astronomical spectra
indicates that only the cage family could contribute to the plateau observed in
the 6-9 micron region. The present framework shows great promise to explore and
relate structural and spectroscopic features in more diverse and possibly
hydrogenated carbonaceous compounds, in relation with astronomical
observations
On the Influence of Magnetic Fields on the Structure of Protostellar Jets
We here present the first results of fully three-dimensional (3-D) MHD
simulations of radiative cooling pulsed (time-variable) jets for a set of
parameters which are suitable for protostellar outflows. Considering different
initial magnetic field topologies in approximate with the
thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which
permeating the jet and the ambient medium; and (iii) a purely toroidal field
permeating only the jet, we find that the overall morphology of the pulsed jet
is not very much affected by the presence of the different magnetic field
geometries in comparison to a nonmagnetic calculation. Instead, the magnetic
fields tend to affect essentially the detailed structure and emission
properties behind the shocks at the head and at the pulse-induced internal
knots, particularly for the helical and toroidal geometries. In these cases, we
find, for example, that the emissivity behind the internal knots can
be about three to four times larger than that of the purely hydrodynamical jet.
We also find that some features, like the nose cones that often develop at the
jet head in 2-D calculations involving toroidal magnetic fields, are smoothed
out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections
(for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar
The precession of the giant HH34 outflow: a possible jet deceleration mechanism
The giant jets represent a fundamental trace of the historical evolution of
the outflow activity over timescales which are comparable to the accretion time
of the outflow sources in their main protostellar phase. The study of such huge
jets provides the possibility of retrieving important elements related to the
life of the outflow sources. In this paper, we study the role of precession
(combined with jet velocity-variability and the resulting enhanced interaction
with the surrounding environment) as a deceleration mechanism for giant jets
using a numerical approach. We obtain predictions of H alpha intensity maps and
position-velocity diagrams from 3D simulations of the giant HH 34 jet
(including an appropriate ejection velocity time-variability and a precession
of the outflow axis), and we compare them with previously published
observations of this object. Our simulations represent a step forward from
previous numerical studies of HH objects, in that the use of a 7-level, binary
adaptive grid has allowed us to compute models which appropiately cover all
relevant scales of a giant jet, from the ~ 100 AU jet radius close to the
source to the ~ 1 pc length of the outflow. A good qualitative and quantitative
agreement is found between the model predictions and the observations.
Moreover, we show that a critical parameter for obtaining a better or worse
agreement with the observations is the ratio rho_j/rho_a between the jet and
the environmental densities. The implications of this result in the context of
the current star formation models are discussed (ABRIDGED).Comment: 19 pages, 8 eps figs.,uses aaspp4; accepted by the Ap
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