1,306 research outputs found
Comparing simulated Al maps to gamma-ray measurements
© ESO 2019.Context. The diffuse gamma-ray emission of at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. Interstellar-medium morphology and dynamics are investigated in astrophysics through 3D hydrodynamic simulations in fine detail, as only few suitable astronomical probes are available. Aims. We compare a galactic-scale hydrodynamic simulation of the Galaxy's interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on emission in the Milky Way extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we perform maximum likelihood fits of simulated sky maps as well as observation-based maximum entropy maps to measurements with INTEGRAL/SPI. To study general morphological properties, we compare the scale heights of emission produced by the simulation to INTEGRAL/SPI measurements.} Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, but differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small scale height features and a mismatch at larger scale heights. We attribute this to the prominent foreground emission sites that are not captured by the simulation.Peer reviewedFinal Accepted Versio
Blueprint for the Dissemination of Evidence-Based Practices in Health Care
Proposes strategies for better dissemination of best practices through quality improvement campaigns, including campaigns aligned with adopting organizations' goals, practical implementation tools and guides, and networks to foster learning opportunities
VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I
We present the first images of the 28SiO v=1, J=2-1 maser emission around the
closest known massive young stellar object Orion Source I observed at 86 GHz
(3mm) with the VLBA. These images have high spatial (~0.3 mas) and spectral
(~0.054 km/s) resolutions. We find that the 3mm masers lie in an X-shaped locus
consisting of four arms, with blue-shifted emission in the south and east arms
and red-shifted emission in the north and west arms. Comparisons with previous
images of the 28SiO v=1,2, J=1-0 transitions at 7mm (observed in 2001-2002)
show that the bulk of the J=2-1 transition emission follows the streamlines of
the J=1-0 emission and exhibits an overall velocity gradient consistent with
the gradient at 7mm. While there is spatial overlap between the 3mm and 7mm
transitions, the 3mm emission, on average, lies at larger projected distances
from Source I (~44 AU compared with ~35 AU for 7mm). The spatial overlap
between the v=1, J=1-0 and J=2-1 transitions is suggestive of a range of
temperatures and densities where physical conditions are favorable for both
transitions of a same vibrational state. However, the observed spatial offset
between the bulk of emission at 3mm and 7mm possibly indicates different ranges
of temperatures and densities for optimal excitation of the masers. We discuss
different maser pumping models that may explain the observed offset. We
interpret the 3mm and 7mm masers as being part of a single wide-angle outflow
arising from the surface of an edge-on disk rotating about a
northeast-southwest axis, with a continuous velocity gradient indicative of
differential rotation consistent with a Keplerian profile in a high-mass
proto-binary.Comment: 11 pages, 12 figures; accepted for publication in A&
Radiation-Hydrodynamic Simulations of Collapse and Fragmentation in Massive Protostellar Cores
We simulate the early stages of the evolution of turbulent, virialized,
high-mass protostellar cores, with primary attention to how cores fragment, and
whether they form a small or large number of protostars. Our simulations use
the Orion adaptive mesh refinement code to follow the collapse from ~0.1 pc
scales to ~10 AU scales, for durations that cover the main fragmentation phase,
using three-dimensional gravito-radiation hydrodynamics. We find that for a
wide range of initial conditions radiation feedback from accreting protostars
inhibits the formation of fragments, so that the vast majority of the collapsed
mass accretes onto one or a few objects. Most of the fragmentation that does
occur takes place in massive, self-shielding disks. These are driven to
gravitational instability by rapid accretion, producing rapid mass and angular
momentum transport that allows most of the gas to accrete onto the central star
rather than forming fragments. In contrast, a control run using the same
initial conditions but an isothermal equation of state produces much more
fragmentation, both in and out of the disk. We conclude that massive cores with
observed properties are not likely to fragment into many stars, so that, at
least at high masses, the core mass function probably determines the stellar
initial mass function. Our results also demonstrate that simulations of massive
star forming regions that do not include radiative transfer, and instead rely
on a barotropic equation of state or optically thin heating and cooling curves,
are likely to produce misleading results.Comment: 23 pages, 18 figures, emulateapj format. Accepted to ApJ. This
version has minor typo fixes and small additions, no significant changes.
Resolution of images severely degraded to fit within size limit. Download the
full paper from http://www.astro.princeton.edu/~krumholz/recent.htm
Contemporary evidence: baseline data from the D2B Alliance
© 2008 Bradley et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Disk and outflow signatures in Orion-KL: The power of high-resolution thermal infrared spectroscopy
We used the CRIRES spectrograph on the VLT to study the ro-vibrational
12CO/13CO, the Pfund beta and H2 emission between 4.59 and 4.72mu wavelengths
toward the BN object, the disk candidate source n, and a proposed dust density
enhancement IRC3. We detected CO absorption and emission features toward all
three targets. Toward the BN object, the data partly confirm the results
obtained more than 25 years ago by Scoville et al., however, we also identify
several new features. While the blue-shifted absorption is likely due to
outflowing gas, toward the BN object we detect CO in emission extending in
diameter to ~3300AU. Although at the observational spectral resolution limit,
the 13CO line width of that feature increases with energy levels, consistent
with a disk origin. If one attributes the extended CO emission also to a disk
origin, its extent is consistent with other massive disk candidates in the
literature. For source n, we also find the blue-shifted CO absorption likely
from an outflow. However, it also exhibits a narrower range of redshifted CO
absorption and adjacent weak CO emission, consistent with infalling motions. We
do not spatially resolve the emission for source n. For both sources we conduct
a Boltzmann analysis of the 13CO absorption features and find temperatures
between 100 and 160K, and H2 column densities of the order a few times
10^23cm^-2. The observational signatures from IRC3 are very different with only
weak absorption against a much weaker continuum source. However, the CO
emission is extended and shows wedge-like position velocity signatures
consistent with jet-entrainment of molecular gas, potentially associated with
the Orion-KL outflow system. We also present and discuss the Pfund beta and H2
emission in the region.Comment: 12 pages, 15 pages, accepted for A&A, you find a high-resolution copy
at http://www.mpia-hd.mpg.de/homes/beuther/papers.htm
Probing the centre of the large circumstellar disc in M17
We investigated the nature of the hitherto unresolved elliptical infrared
emission in the centre of the ~20000 AU disc silhouette in M 17. We combined
high-resolution JHKsL'M' band imaging carried out with NAOS/CONICA at the VLT
with [Fe II] narrow band imaging using SOFI at the NTT. The analysis is
supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT
Integral Field Spectroscopy data. For the first time, we resolve the elongated
central infrared emission into a point-source and a jet-like feature that
extends to the northeast in the opposite direction of the recently discovered
collimated H2 jet. They are both orientated almost perpendicular to the disc
plane. In addition, our images reveal a curved southwestern emission nebula
whose morphology resembles that of the previously detected northeastern one.
Both nebulae are located at a distance of 1500 AU from the disc centre. We
describe the infrared point-source in terms of a protostar that is embedded in
circumstellar material producing a visual extinction of 60 <= Av <= 82. The
observed Ks band magnitude is equivalent to a stellar mass range of 2.8 Msun <=
Mstar <= 8 Msun adopting conversions for a main-sequence star. Altogether, we
suggest that the large M 17 accretion disc is forming an intermediate to
high-mass protostar. Part of the accreted material is expelled through a
symmetric bipolar jet/outflow.Comment: 6 pages, 3 figures, accepted by MNRAS (16 May 2008
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