247 research outputs found
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
Interaction of Infall and Winds in Young Stellar Objects
The interaction of a stellar or disk wind with a collapsing environment holds
promise for explaining a variety of outflow phenomena observed around young
stars. In this paper we present the first simulations of these interactions.
The focus here is on exploring how ram pressure balance between wind and
ambient gas and post-shock cooling affects the shape of the resulting outflows.
In our models we explore the role of ram pressure and cooling by holding the
wind speed constant and adjusting the ratio of the inflow mass flux to the wind
mass flux (Mdot_a/Mdot_w) Assuming non-spherical cloud collapse, we find that
relatively strong winds can carve out wide, conical outflow cavities and that
relatively weak winds can be strongly collimated into jet-like structures. If
the winds become weak enough, they can be cut off entirely by the infalling
environment. We identify discrepancies between results from standard snowplow
models and those presented here that have important implications for molecular
outflows. We also present mass vs. velocity curves for comparison with
observations.Comment: 35 pages, 11 figures (PNG and EPS
Jets and Outflows From Star to Cloud: Observations Confront Theory
In this review we focus on the role jets and outflows play in the star and
planet formation process. Our essential question can be posed as follows: are
jets/outflows merely an epiphenomenon associated with star formation or do they
play an important role in mediating the physics of assembling stars both
individually and globally? We address this question by reviewing the current
state of observations and their key points of contact with theory. Our review
of jet/outflow phenomena is organized into three length-scale domains: Source
and Disk Scales ( au) where the connection with protostellar and disk
evolution theories is paramount; Envelope Scales ( au) where the
chemistry and propagation shed further light on the jet launching process, its
variability and its impact on the infalling envelope; Parent Cloud Scales
( au) where global momentum injection into cluster/cloud
environments become relevant. Issues of feedback are of particular importance
on the smallest scales where planet formation regions in a disk may be impacted
by the presence of disk winds, irradiation by jet shocks or shielding by the
winds. Feedback on envelope scales may determine the final stellar mass
(core-to-star efficiency) and envelope dissipation. Feedback also plays an
important role on the larger scales with outflows contributing to turbulent
support within clusters including alteration of cluster star formation
efficiencies (feedback on larger scales currently appears unlikely). A
particularly novel dimension of our review is that we consider results on jet
dynamics from the emerging field of High Energy Density Laboratory Astrophysics
(HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully
magnetized, hypersonic, radiative outflows.Comment: Accepted for publication as a chapter in Protostars and Planets VI,
University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C.
Dullemond, Th. Hennin
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
Guillain-Barré Syndrome Associated with Primary Parvovirus B19 Infection in an HIV-1-Infected Patient
Parvovirus B19 (B19V) infection has rarely been reported as responsible for Guillain-Barré syndrome (GBS). We present the case of a 63-year-old man with AIDS who presented with rapidly progressing weakness of his inferior limbs and a newly appeared pancytopenia. CSF examination and electromyography were characteristic for GBS. Very high CSF and serum B19V DNA concentrations were present, in the absence of IgG or IgM against B19V. The neurologic and hematologic abnormalities improved after a 5-day course of i.v. immunoglobulins in parallel with a dramatic decrease in the B19V viral load
The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo
We performed a deep wide field optical survey of the young (~100-150 Myr)
open cluster Blanco1 to study its low mass population well down into the brown
dwarf regime and estimate its mass function over the whole cluster mass
range.The survey covers 2.3 square degrees in the I and z-bands down to I ~ z ~
24 with the CFH12K camera. Considering two different cluster ages (100 and 150
Myr), we selected cluster member candidates on the basis of their location in
the (I,I-z) CMD relative to the isochrones, and estimated the contamination by
foreground late-type field dwarfs using statistical arguments, infrared
photometry and low-resolution optical spectroscopy. We find that our survey
should contain about 57% of the cluster members in the 0.03-0.6 Mo mass range,
including 30-40 brown dwarfs. The candidate's radial distribution presents
evidence that mass segregation has already occured in the cluster. We took it
into account to estimate the cluster mass function across the
stellar/substellar boundary. We find that, between 0.03Mo and 0.6Mo, the
cluster mass distribution does not depend much on its exact age, and is well
represented by a single power-law, with an index alpha=0.69 +/- 0.15. Over the
whole mass domain, from 0.03Mo to 3Mo, the mass function is better fitted by a
log-normal function with m0=0.36 +/- 0.07Mo and sigma=0.58 +/- 0.06. Comparison
between the Blanco1 mass function, other young open clusters' MF, and the
galactic disc MF suggests that the IMF, from the substellar domain to the
higher mass part, does not depend much on initial conditions. We discuss the
implications of this result on theories developed to date to explain the origin
of the mass distribution.Comment: 18 pages, 15 figures and 5 tables accepted in A&
SPIRITS 15c and SPIRITS 14buu: Two Obscured Supernovae in the Nearby Star-Forming Galaxy IC 2163
SPIRITS---SPitzer InfraRed Intensive Transients Survey---is an ongoing survey
of nearby galaxies searching for infrared (IR) transients with Spitzer/IRAC. We
present the discovery and follow-up observations of one of our most luminous
( mag, Vega) and red (
mag) transients, SPIRITS 15c. The transient was detected in a dusty spiral arm
of IC 2163 ( Mpc). Pre-discovery ground-based imaging revealed an
associated, shorter-duration transient in the optical and near-IR (NIR). NIR
spectroscopy showed a broad ( km s), double-peaked
emission line of He I at m, indicating an explosive origin. The NIR
spectrum of SPIRITS 15c is similar to that of the Type IIb SN 2011dh at a phase
of days. Assuming mag of extinction in SPIRITS 15c
provides a good match between their optical light curves. The IR light curves
and the extreme color cannot be explained using only a standard
extinction law. Another luminous ( mag) event, SPIRITS
14buu, was serendipitously discovered in the same galaxy. The source displays
an optical plateau lasting days, and we suggest a scenario similar
to the low-luminosity Type IIP SN 2005cs obscured by mag.
Other classes of IR-luminous transients can likely be ruled out in both cases.
If both events are indeed SNe, this may suggest of nearby
core-collapse SNe are missed by currently operating optical surveys.Comment: 19 pages, 7 Figures, 4 Table
Outflow Driven Turbulence in Molecular Clouds
In this paper we explore the relationship between protostellar outflows and
turbulence in molecular clouds. Using 3-D numerical simulations we focus on the
hydrodynamics of multiple outflows interacting within a parsec scale volume. We
explore the extent to which transient outflows injecting directed energy and
momentum into a sub-volume of a molecular cloud can be converted into random
turbulent motions. We show that turbulence can readily be sustained by these
interactions and show that it is possible to broadly characterize an effective
driving scale of the outflows. We compare the velocity spectrum obtained in our
studies to that of isotropically forced hydrodynamic turbulence finding that in
outflow driven turbulence a power law is indeed achieved. However we find a
steeper spectrum (beta ~ 3) is obtained in outflow driven turbulence models
than in isotropically forced simulations (beta ~ 2). We discuss possible
physical mechanisms responsible for these results as well and their
implications for turbulence in molecular clouds where outflows will act in
concert with other processes such as gravitational collapse.Comment: 12 pages, 3 figure
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