2,841 research outputs found
The Evolution of Hetergeneous "Clumpy Jets": A Parameter Study
We investigate the role discrete clumps embedded in an astrophysical jet play
on the jet's morphology and line emission characteristics. By varying clumps'
size, density, position, and velocity, we cover a range of parameter space
motivated by observations of objects such as the Herbig Haro object HH~34. We
here extend the results presented in Yirak et al. 2009, including how analysis
of individual observations may lead to spurious sinusoidal variation whose
parameters vary widely over time, owing chiefly to interacts between clumps.
The goodness of the fits, while poor in all simulations, are best when
clump-clump collisions are minimal. Our results indicate that a large velocity
dispersion leads to a clump-clump collision-dominated flow which disrupts the
jet beam. Finally, we present synthetic emission images of H- and [SII]
and note an excess of [SII] emission along the jet length as compared to
observations. This suggests that observed beams undergo earlier processing, if
they are present at all.Comment: 18 pages, 7 figures. Submitted to the Astrophysical Journa
âGenuine Brotherhoodâ without Remorse: A Commentary on Joseph Ratzingerâs "Comments on 'De Iudaeis'"
This article critically engages, section by section, a 2018 essay on Catholic-Jewish relations by emeritus Pope Benedict XVI. It is the result of joint analysis by a Jewish professor and a Catholic professor who co-direct an academic institute devoted to Catholic-Jewish relations. Benedictâs treatment of such topics as supersessionism, the âunrevoked covenant,â and the State of Israel is complex, and his reasoning is often difficult to follow, but the authors conclude that his essay makes genuine contributions to a Catholic theology of relations with Jews and Judaism that deserve serious, dispassionate, and critical study. This is true despite some serious weaknesses, especially its lack of consistent engagement with Judaism as lived by Jews today
Primer for the Transportable Applications Executive
The Transportable Applications Executive (TAE), an interactive multipurpose executive that provides commonly required functions for scientific analysis systems, is discussed. The concept of an executive is discussed and the various components of TAE are presented. These include on-line help information, the use of menus or commands to access analysis programs, and TAE command procedures
Protostellar Outflow Evolution in Turbulent Environments
The link between turbulence in star formatting environments and protostellar
jets remains controversial. To explore issues of turbulence and fossil cavities
driven by young stellar outflows we present a series of numerical simulations
tracking the evolution of transient protostellar jets driven into a turbulent
medium. Our simulations show both the effect of turbulence on outflow
structures and, conversely, the effect of outflows on the ambient turbulence.
We demonstrate how turbulence will lead to strong modifications in jet
morphology. More importantly, we demonstrate that individual transient outflows
have the capacity to re-energize decaying turbulence. Our simulations support a
scenario in which the directed energy/momentum associated with cavities is
randomized as the cavities are disrupted by dynamical instabilities seeded by
the ambient turbulence. Consideration of the energy power spectra of the
simulations reveals that the disruption of the cavities powers an energy
cascade consistent with Burgers'-type turbulence and produces a driving
scale-length associated with the cavity propagation length. We conclude that
fossil cavities interacting either with a turbulent medium or with other
cavities have the capacity to sustain or create turbulent flows in star forming
environments. In the last section we contrast our work and its conclusions with
previous studies which claim that jets can not be the source of turbulence.Comment: 24 pages, submitted to the Astrophysical Journa
Isotropically Driven versus Outflow Driven Turbulence: Observational Consequences for Molecular Clouds
Feedback from protostellar outflows can influence the nature of turbulence in
star forming regions even if they are not the primary source of velocity
dispersion for all scales of molecular clouds. For the rate and power expected
in star forming regions, we previously (Carroll et al. 2009) demonstrated that
outflows could drive supersonic turbulence at levels consistent with the
scaling relations from Matzner 2007 although with a steeper velocity power
spectrum than expected for an isotropically driven supersonic turbulent
cascade. Here we perform higher resolution simulations and combine simulations
of outflow driven turbulence with those of isotropically forced turbulence. We
find that the presence of outflows within an ambient isotropically driven
turbulent environment produces a knee in the velocity power spectrum at the
outflow scale and a steeper slope at sub-outflow scales than for a purely
isotropically forced case. We also find that the presence of outflows flattens
the density spectrum at large scales effectively reducing the formation of
large scale turbulent density structures. These effects are qualitatively
independent of resolution. We have also carried out Principal Component
Analysis (PCA) for synthetic data from our simulations. We find that PCA as a
tool for identifying the driving scale of turbulence has a misleading bias
toward low amplitude large scale velocity structures even when they are not
necessarily the dominant energy containing scales. This bias is absent for
isotropically forced turbulence but manifests strongly for collimated outflow
driven turbulence.Comment: 30 pages, 10 figures, Submitted to Ap
Hypersonic Buckshot: Astrophysical Jets as Heterogeneous Collimated Plasmoids
Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma
traveling at hypersonic velocities. Structure within jet beams is often
attributed to periodic or ``pulsed'' variations of conditions at the jet
source. Simulations based on this scenario result in knots extending across the
jet diameter. Observations and recent high energy density laboratory
experiments shed new light on structures below this scale and indicate they may
be important for understanding the fundamentals of jet dynamics. In this paper
we offer an alternative to ``pulsed'' models of protostellar jets. Using direct
numerical simulations we explore the possibility that jets are chains of
sub-radial clumps propagating through a moving inter-clump medium. Our models
explore an idealization of this scenario by injecting small (),
dense () spheres embedded in an otherwise smooth inter-clump
jet flow. The spheres are initialized with velocities differing from the jet
velocity by %. We find the consequences of shifting from homogeneous to
heterogeneous flows are significant as clumps interact with each other and with
the inter-clump medium in a variety of ways. Structures which mimic what is
expected from pulsed-jet models can form, as can previously unseen
``sub-radial'' behaviors including backward facing bow shocks and off-axis
working surfaces. While these small-scale structures have not been seen before
in simulation studies, they are found in high resolution jet observations. We
discuss implications of our simulations for the interpretation of protostellar
jets with regard to characterization of knots by a ``lifetime'' or ``velocity
history'' approach as well as linking observed structures with central engines
which produce the jets.Comment: 15 pages, 3 figures (1 color), submitted to Ap
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