3,808 research outputs found
A mid-IR survey of the L 1641-N region with ISOCAM
We present an analysis of the L 1641 outflow region using broad-band and
narrow-band imaging data at mid-infrared wavelengths from ISOCAM. We detect a
total of 34 sources in the x region covered by
the broad-band filters. Four of these sources have no reported detection in
previous studies of the region. We find that the source previously identified
as the near-IR counter-part to the IRAS detected point-source (IRAS 05338-0624)
is not the brightest source in the wavelength region of the IRAS 12 \micron\
filter. We find instead that a nearby object (within the beam of IRAS and not
detected at near-IR wavelengths) outshines all others sources in the area by a
factor of 2. We submit that this source is likely to be the IRAS detected
point source. A comparison of the near-IR (J-H vs H-K) and mid-IR (J-K vs [6.7
um]-[14 um]) color-color plots shows only four sources with excess emission at
near-IR wavelengths, but atleast 85% of all sources show excess emission at
mid-IR wavelengths. The CVF spectra suggest a range of evolutionary status in
the program stars ranging from embedded YSOs to the young disks. When combined
with optical and near-IR age estimates, these results show active current
star-formation in the region that has been on-going for at least 2 Myr.Comment: Submitted to ApJ. Abstracted edited for arXiv submission Replaced by
version accepted by Ap
Launch Environment Water Flow Simulations Using Smoothed Particle Hydrodynamics
This paper describes the use of Smoothed Particle Hydrodynamics (SPH) to simulate the water flow from the rainbird nozzle system used in the sound suppression system during pad abort and nominal launch. The simulations help determine if water from rainbird nozzles will impinge on the rocket nozzles and other sensitive ground support elements
Controlled Anisotropic Deformation of Ag Nanoparticles by Si Ion Irradiation
The shape and alignment of silver nanoparticles embedded in a glass matrix is
controlled using silicon ion irradiation. Symmetric silver nanoparticles are
transformed into anisotropic particles whose larger axis is along the ion beam.
Upon irradiation, the surface plasmon resonance of symmetric particles splits
into two resonances whose separation depends on the fluence of the ion
irradiation. Simulations of the optical absorbance show that the anisotropy is
caused by the deformation and alignment of the nanoparticles, and that both
properties are controlled with the irradiation fluence.Comment: Submitted to Phys. Rev. Lett. (October 14, 2005
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
Statistical -decay from highly excited states is determined by the
nuclear level density (NLD) and the -ray strength function
(SF). These average quantities have been measured for several nuclei
using the Oslo method. For the first time, we exploit the NLD and SF to
evaluate the -width in the energy region below the neutron binding
energy, often called the quasi-continuum region. The lifetimes of states in the
quasi-continuum are important benchmarks for a theoretical description of
nuclear structure and dynamics at high temperature. The lifetimes may also have
impact on reaction rates for the rapid neutron-capture process, now
demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure
Completing the nuclear reaction puzzle of the nucleosynthesis of 92Mo
One of the greatest questions for modern physics to address is how elements
heavier than iron are created in extreme, astrophysical environments. A
particularly challenging part of that question is the creation of the so-called
p-nuclei, which are believed to be mainly produced in some types of supernovae.
The lack of needed nuclear data presents an obstacle in nailing down the
precise site and astrophysical conditions. In this work, we present for the
first time measurements on the nuclear level density and average strength
function of Mo. State-of-the-art p-process calculations systematically
underestimate the observed solar abundance of this isotope. Our data provide
stringent constraints on the NbMo reaction rate,
which is the last unmeasured reaction in the nucleosynthesis puzzle of
Mo. Based on our results, we conclude that the Mo abundance
anomaly is not due to the nuclear physics input to astrophysical model
calculations.Comment: Submitted to PR
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
A 3-mode, Variable Velocity Jet Model for HH 34
Variable ejection velocity jet models can qualitatively explain the
appearance of successive working surfaces in Herbig-Haro (HH) jets. This paper
presents an attempt to explore which features of the HH-34 jet can indeed be
reproduced by such a model. From previously published data on this object, we
find evidence for the existence of a 3-mode ejection velocity variability, and
then explore the implications of such a variability. From simple, analytic
considerations it is possible to show that the longer period modes produce a
modulation on the shorter period modes, resulting in the formation of
``trains'' of multiple knots. The knots observed close to the source of HH-34
could correspond to such a structure. Finally, a numerical simulation with the
ejection velocity variability deduced from the HH-34 data is computed. This
numerical simulation shows a quite remarkable resemblance with the observed
properties of the HH-34 jet.Comment: 28 pages LaTex, 10 postscript figure
High-accuracy Penning trap mass measurements with stored and cooled exotic ions
The technique of Penning trap mass spectrometry is briefly reviewed
particularly in view of precision experiments on unstable nuclei, performed at
different facilities worldwide. Selected examples of recent results emphasize
the importance of high-precision mass measurements in various fields of
physics
XTE J0111.2-7317 : a nebula-embedded X-ray binary in the SMC
The observed characteristics of the nebulosity surrounding the SMC High Mass
X-ray Binary XTE J0111.2-7317 are examined in the context of three possible
nebular types: SNR, bowshock and HII region. Observational evidence is
presented which appears to support the interpretation that the nebulosity
surrounding XTE J0111.2-7317 is an HII region. The source therefore appears to
be a normal SMC Be X-ray binary (BeXRB) embedded in a locally enhanced ISM
which it has photoionised to create an HII region. This is supported by
observations of the X-ray outburst seen with BATSE and RXTE in 1998-1999. It
exhibited characteristics typical of a giant or type II outburst in a BeXRB
including large spin-up rates, Lx~10E38 erg/sq.cm-s, and a correlation between
spin-up rate and pulsed flux. However, the temporal profile of the outburst was
unusual, consisting of two similar intensity peaks, with the first peak of
shorter duration than the second.Comment: Accepted for publication by MNRA
Statistical properties of Pu, and Pu(n,) cross section calculation
The level density and gamma-ray strength function (gammaSF) of 243Pu have
been measured in the quasi-continuum using the Oslo method. Excited states in
243Pu were populated using the 242Pu(d,p) reaction. The level density closely
follows the constant-temperature level density formula for excitation energies
above the pairing gap. The gammaSF displays a double-humped resonance at low
energy as also seen in previous investigations of actinide isotopes. The
structure is interpreted as the scissors resonance and has a centroid of
omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is
in excellent agreement with sum-rule estimates. The measured level density and
gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron
energy range for which there were previously no measured data.Comment: 9 pages, 8 figure
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