2,581 research outputs found
Disk wind feedback from high-mass protostars
We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the
outflow-core interaction for a massive protostar forming via collapse of an
initial cloud core of . This allows us to characterize the
properties of disk wind driven outflows from massive protostars, which can
allow testing of different massive star formation theories. It also enables us
to assess quantitatively the impact of outflow feedback on protostellar core
morphology and overall star formation efficiency. We find that the opening
angle of the flow increases with increasing protostellar mass, in agreement
with a simple semi-analytic model. Once the protostar reaches
the outflow's opening angle is so wide that it has blown
away most of the envelope, thereby nearly ending its own accretion. We thus
find an overall star formation efficiency of , similar to that
expected from low-mass protostellar cores. Our simulation results therefore
indicate that the MHD disk wind outflow is the dominant feedback mechanism for
helping to shape the stellar initial mass function from a given prestellar core
mass function.Comment: Accepted for publication in Ap
Outflow-Confined HII regions. II. The Early Break-Out Phase
In this series of papers, we model the formation and evolution of the
photoionized region and its observational signatures during massive star
formation. Here we focus on the early break out of the photoionized region into
the outflow cavity. Using results of 3-D magnetohydrodynamic-outflow
simulations and protostellar evolution calculations, we perform post-processing
radiative-transfer. The photoionized region first appears at a protostellar
mass of 10Msun in our fiducial model, and is confined to within 10-100AU by the
dense inner outflow, similar to some observed very small hypercompact HII
regions. Since the ionizing luminosity of the massive protostar increases
dramatically as Kelvin-Helmholz (KH) contraction proceeds, the photoionized
region breaks out to the entire outflow region in <10,000yr. Accordingly, the
radio free-free emission brightens significantly in this stage. In our fiducial
model, the radio luminosity at 10 GHz changes from 0.1 mJy kpc2 at m=11Msun to
100 mJy kpc2 at 16Msun, while the infrared luminosity increases by less than a
factor of two. The radio spectral index also changes in the break-out phase
from the optically thick value of 2 to the partially optically thin value of
0.6. Additionally, we demonstrate that short-timescale variation in free-free
flux would be induced by an accretion burst. The outflow density is enhanced in
the accretion burst phase, which leads to a smaller ionized region and weaker
free-free emission. The radio luminosity may decrease by one order of magnitude
during such bursts, while the infrared luminosity is much less affected, since
internal protostellar luminosity dominates over accretion luminosity after KH
contraction starts. Such variability may be observable on timescales as short
10-100 yr, if accretion bursts are driven by disk instabilities.Comment: 9 pages, 5 figures, accepted for publication in Ap
Radiocarbon dates from the Oxford AMS system: archaeometry datelist 35
This is the 35th list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst some of the sites included here are the latest series of determinations from the key sites of Abydos, El Mirón, Ban Chiang, Grotte de Pigeons (Taforalt), Alepotrypa and Oberkassel, as well as others dating to the Palaeolithic, Mesolithic and later periods. Comments on the significance of the results are provided by the submitters of the material
The role of dredge-up in double white dwarf mergers
We present the results of an investigation of the dredge-up and mixing during
the merger of two white dwarfs with different chemical compositions by
conducting hydrodynamic simulations of binary mergers for three representative
mass ratios. In all the simulations, the total mass of the two white dwarfs is
. Mergers involving a CO and a He white dwarf have
been suggested as a possible formation channel for R Coronae Borealis type
stars, and we are interested in testing if such mergers lead to conditions and
outcomes in agreement with observations. Even if the conditions during the
merger and subsequent nucleosynthesis favor the production of , the merger must avoid dredging up large amounts of , or
else it will be difficult to produce sufficient to explain
the oxygen ratio observed to be of order unity. We performed a total of 9
simulations using two different grid-based hydrodynamics codes using fixed and
adaptive meshes, and one smooth particle hydrodynamics (SPH) code. We find that
in most of the simulations, of is
indeed dredged up during the merger. However, in SPH simulations where the
accretor is a hybrid He/CO white dwarf with a layer of
helium on top, we find that no is being dredged up, while in
the simulation of has been
brought up, making a WD binary consisting of a hybrid CO/He WD and a companion
He WD an excellent candidate for the progenitor of RCB stars.Comment: Accepted for publication in Ap
The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results
We present an overview and first results of the Stratospheric Observatory For
Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the
FORCAST instrument to image massive protostars from
--. These wavelengths trace thermal emission from
warm dust, which in Core Accretion models mainly emerges from the inner regions
of protostellar outflow cavities. Dust in dense core envelopes also imprints
characteristic extinction patterns at these wavelengths, causing intensity
peaks to shift along the outflow axis and profiles to become more symmetric at
longer wavelengths. We present observational results for the first eight
protostars in the survey, i.e., multiwavelength images, including some
ancillary ground-based MIR observations and archival {\it{Spitzer}} and
{\it{Herschel}} data. These images generally show extended MIR/FIR emission
along directions consistent with those of known outflows and with shorter
wavelength peak flux positions displaced from the protostar along the
blueshifted, near-facing sides, thus confirming qualitative predictions of Core
Accretion models. We then compile spectral energy distributions and use these
to derive protostellar properties by fitting theoretical radiative transfer
models. Zhang and Tan models, based on the Turbulent Core Model of McKee and
Tan, imply the sources have protostellar masses --50
accreting at -- inside cores of
initial masses --500 embedded in clumps with mass surface
densities --3. Fitting Robitaille
et al. models typically leads to slightly higher protostellar masses, but with
disk accretion rates smaller. We discuss reasons for these
differences and overall implications of these first survey results for massive
star formation theories.Comment: Accepted to ApJ, 32 page
The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars
We present multi-wavelength images observed with SOFIA-FORCAST from 10
to 40 m of seven high luminosity massive protostars, as part of the SOFIA
Massive (SOMA) Star Formation Survey. Source morphologies at these wavelengths
appear to be influenced by outflow cavities and extinction from dense gas
surrounding the protostars. Using these images, we build spectral energy
distributions (SEDs) of the protostars, also including archival data from
Spitzer, Herschel and other facilities. Radiative transfer (RT) models of Zhang
& Tan (2018), based on Turbulent Core Accretion theory, are then fit to the
SEDs to estimate key properties of the protostars. Considering the best five
models fit to each source, the protostars have masses accreting at rates of inside cores of initial masses embedded in clumps with mass surface densities and span a luminosity range of . Compared with the first eight protostars in Paper I, the sources
analyzed here are more luminous, and thus likely to be more massive protostars.
They are often in a clustered environment or have a companion protostar
relatively nearby. From the range of parameter space of the models, we do not
see any evidence that needs to be high to form these massive
stars. For most sources the RT models provide reasonable fits to the SEDs,
though the cold clump material often influences the long wavelength fitting.
However, for sources in very clustered environments, the model SEDs may not be
such a good description of the data, indicating potential limitations of the
models for these regions.Comment: 30 pages, 19 figures, Accepted for publication in Ap
A Massive Protostar Forming by Ordered Collapse of a Dense, Massive Core
We present 30 and 40 micron imaging of the massive protostar G35.20-0.74 with
SOFIA-FORCAST. The high surface density of the natal core around the protostar
leads to high extinction, even at these relatively long wavelengths, causing
the observed flux to be dominated by that emerging from the near-facing outflow
cavity. However, emission from the far-facing cavity is still clearly detected.
We combine these results with fluxes from the near-infrared to mm to construct
a spectral energy distribution (SED). For isotropic emission the bolometric
luminosity would be 3.3x10^4 Lsun. We perform radiative transfer modeling of a
protostar forming by ordered, symmetric collapse from a massive core bounded by
a clump with high mass surface density, Sigma_cl. To fit the SED requires
protostellar masses ~20-34 Msun depending on the outflow cavity opening angle
(35 - 50 degrees), and Sigma_cl ~ 0.4-1 g cm-2. After accounting for the
foreground extinction and the flashlight effect, the true bolometric luminosity
is ~ (0.7-2.2)x10^5 Lsun. One of these models also has excellent agreement with
the observed intensity profiles along the outflow axis at 10, 18, 31 and 37
microns. Overall our results support a model of massive star formation
involving the relatively ordered, symmetric collapse of a massive, dense core
and the launching bipolar outflows that clear low density cavities. Thus a
unified model may apply for the formation of both low and high mass stars.Comment: 6 pages, 4 figures, 1 table, accepted to Ap
Skin Extracellular Matrix Breakdown Following Paclitaxel Therapy in Patients with Chemotherapy-Induced Peripheral Neuropathy.
The chemotherapeutic agent paclitaxel causes peripheral neuropathy, a dose-limiting side effect, in up to 68% of cancer patients. In this study, we investigated the impact of paclitaxel therapy on the skin of breast cancer patients with chemotherapy-induced peripheral neuropathy (CIPN), building upon previous findings in zebrafish and rodents. Comprehensive assessments, including neurological examinations and quality of life questionnaires, were conducted, followed by intraepidermal nerve fiber (IENF) density evaluations using skin punch biopsies. Additionally, RNA sequencing, immunostaining for Matrix-Metalloproteinase 13 (MMP-13), and transmission electron microscopy provided insights into molecular and ultrastructural changes in this skin. The results showed no significant difference in IENF density between the control and CIPN patients despite the presence of patient-reported CIPN symptoms. Nevertheless, the RNA sequencing and immunostaining on the skin revealed significantly upregulated MMP-13, which is known to play a key role in CIPN caused by paclitaxel therapy. Additionally, various genes involved in the regulation of the extracellular matrix, microtubules, cell cycle, and nervous system were significantly and differentially expressed. An ultrastructural examination of the skin showed changes in collagen and basement membrane structures. These findings highlight the presence of CIPN in the absence of IENF density changes and support the role of skin remodeling as a major contributor to CIPN
Radiation Transfer of Models of Massive Star Formation. I. Dependence on Basic Core Properties
Radiative transfer calculations of massive star formation are presented.
These are based on the Turbulent Core Model of McKee & Tan and
self-consistently included a hydrostatic core, an inside-out expansion wave, a
zone of free-falling rotating collapse, wide-angle dust-free outflow cavities,
an active accretion disk, and a massive protostar. For the first time for such
models, an optically thick inner gas disk extends inside the dust destruction
front. This is important to conserve the accretion energy naturally and for its
shielding effect on the outer region of the disk and envelope. The simulation
of radiation transfer is performed with the Monte Carlo code of Whitney,
yielding spectral energy distributions (SEDs) for the model series, from the
simplest spherical model to the fiducial one, with the above components each
added step-by-step. Images are also presented in different wavebands of various
telescope cameras, including Spitzer IRAC and MIPS, SOFIA FORCAST and Herschel
PACS and SPIRE. The existence of the optically thick inner disk produces higher
optical wavelength fluxes but reduces near- and mid-IR emission. The presence
of outflow cavities, the inclination angle to the line of sight, and the
thickness of the disk all affect the SEDs and images significantly. For the
high mass surface density cores considered here, the mid-IR emission can be
dominated by the outflow cavity walls, as has been suggested by De Buizer. The
effect of varying the pressure of the environment bounding the surface of the
massive core is also studied. With lower surface pressures, the core is larger,
has lower extinction and accretion rates, and the observed mid-IR flux from the
disk can then be relatively high even though the accretion luminosity is lower.
In this case the silicate absorption feature becomes prominent, in contrast to
higher density cores forming under higher pressures.Comment: 19 pages, 14 figures, 2 tables, accepted for publication in Ap
Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquà River Catchment, Eastern Cordillera, NW Argentina
Unraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles, 10Be-derived catchment mean modern and paleo-erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquà River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base-level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo-erosion rates, ranging from 56 +43/-19 to 105 +60/-33 mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic 10Be. However, punctuated abandonment of pediment and strath terraces at 43.6 +15.0/-11.6, 91.2 +54.2/-22.2, and 151 +92.7/-34.1 ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long-term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional-scale studies which find precipitation to exert the dominant control
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