1,600 research outputs found
HH 223: a parsec-scale H2 outflow in the star-forming region L723
The dark cloud Lynds 723 (L723) is a low-mass star-forming region where one
of the few known cases of a quadrupolar CO outflow has been reported. Two
recent works have found that the radio continuum source VLA 2, towards the
centre of the CO outflow, is actually a multiple system of young stellar
objects (YSOs). Several line-emission nebulae that lie projected on the
east-west CO outflow were detected in narrow-band Halpha and [SII] images. The
spectra of the knots are characteristic of shock-excited gas (Herbig-Haro
spectra), with supersonic blueshifted velocities, which suggests an optical
outflow also powered by the VLA 2 YSO system of L723. We imaged a field of ~5'
X 5' centred on HH 223, which includes the whole region of the quadrupolar CO
outflow with nir narrow-band filters . The H2 line-emission structures appear
distributed over a region of 5.5' (0.5 pc for a distance of 300 pc) at both
sides of the VLA 2 YSO system, with an S-shape morphology, and are projected
onto the east-west CO outflow. Most of them were resolved in smaller knotty
substructures. The [FeII] emission only appears associated with HH 223. An
additional nebular emission from the continuum in Hc and Kc appears associated
with HH 223-K1, the structure closest to the VLA 2 YSO system, and could be
tracing the cavity walls. We propose that the H2 structures form part of a
large-scale near-infrared outflow, which is also associated with the VLA 2 YSO
system. The current data do not allow us to discern which of the YSOs of VLA 2
is powering this large scale optical/near-infrared outflow.Comment: Accepted for A&A http://dx.doi.org/10.1051/0004-6361/201015125 12
pages, 9 figure
Short-Term Effect of Daily Herbage Allowance Restriction on Pasture Condition and the Performance of Grazing Dairy Cows during Autumn
The aim of this study was to evaluate the short-term effects of daily herbage allowance (DHA, defined as the product of pre-grazing herbage mass and offered area per animal) on pasture conditions and milk production of Holstein-Friesian dairy cows. Forty-four early lactation dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design that tested two levels of DHA (17 and 25 kg DM/cow.day) and two levels of maize silage supplementation (MSS, 4.5 and 9 kg DM/cow.day) over a 77-day period. Low DHA decreased the post-grazing herbage mass from 1546 to 1430 kg DM/ha and the compressed sward height from 5 to 4.4 cm, while the grazing efficiency remained unaffected. Low DHA induced a faster herbage mass reduction, while the sward-height and pasture characteristics did not differ from the high DHA regime. Low DHA decreased the tiller production rates and daily lamina growth, while the leaf-production rate was not affected by the DHA. Daily increases of herbage mass were greater in the high DHA than in the low DHA treatments.
Individual milk production and milk protein concentration decreased at a low DHA compared to high DHA, while the milk fat concentration was greater and the milk output per hectare increased by 1510 kg. Neither the MSS level nor the interaction DHA by the MSS level had any effect on the sward characteristics or the productivity of the cows. From these results, it is suggested that,in a high-quality pasture, using 17 kg DM/cow.day was appropriate for improving both herbage utilization and milk production per hectare while maintaining the short-term conditions of a pasture grazed by dairy cows in the autumn
In the quest of specific-domain ontology components for the semantic web
This paper describes an approach we have been using to identify specific-domain ontology components by using Self-Organizing Maps. These components are clustered together in a natural way according to their similarity. The knowledge maps, as we call them, show colored regions containing knowledge components that may be used to populate an specific-domain ontology. Later, these ontology may be used by software agents to carry out basic reasoning task on our behalf. In particular, we deal with the issue of not constructing the ontology from scratch, our approach helps us to speed up the ontology creation process
Possible Tomography of the Sun's Magnetic Field with Solar Neutrinos
The data from solar neutrino experiments together with standard solar model
predictions are used in order to derive the possible profile of the magnetic
field inside the Sun, assuming the existence of a sizeable neutrino magnetic
moment and the resonant spin flavour mechanism. The procedure is based on the
relationship between resonance location and the energy dependent neutrino
suppression, so that a large neutrino suppression at a given energy is taken to
be connected to a large magnetic field in a given region of the Sun. In this
way it is found that the solar field must undergo a very sharp increase by a
factor of at least 6 - 7 over a distance no longer than 7 - 10% of the solar
radius, decreasing gradually towards the surface. The range in which this sharp
increase occurs is likely to be the bottom of the convective zone. There are
also indications in favour of the downward slope being stronger at the start
and more moderate on approaching the solar surface. Typical ranges for the
magnetic moment are from a few times 10^{-13}\mu_B to its laboratory upper
bounds while the mass square difference between neutrino flavours is of order
(0.6-1.9) x 10^{-8}eV^2.Comment: Several minor corrections performed, sunspot anticorrelation
discussed, references added, 29 pages including 8 figures in PostScrip
Neutrino magnetic moments, flavor mixing, and the SuperKamiokande solar data
We find that magnetic neutrino-electron scattering is unaffected by
oscillations for vacuum mixing of Dirac neutrinos with only diagonal moments
and for Majorana neutrinos with two flavors. For MSW mixing, these cases again
obtain, though the effective moments can depend on the neutrino energy. Thus,
e.g., the magnetic moments measured with from a reactor and
from the Sun could be different. With minimal assumptions, we find a
new limit on using the 825-days SuperKamiokande solar neutrino
data: at 90% CL, comparable to the
existing reactor limit.Comment: 4 pages including two inline figures. New version has 825 days SK
result, some minor revisions. Accepted for Physical Review Letter
Using radio astronomical receivers for molecular spectroscopic characterization in astrochemical laboratory simulations: A proof of concept
We present a proof of concept on the coupling of radio astronomical receivers
and spectrometers with chemical reactorsand the performances of the resulting
setup for spectroscopy and chemical simulations in laboratory astrophysics.
Several experiments including cold plasma generation and UV photochemistry were
performed in a 40\,cm long gas cell placed in the beam path of the Aries 40\,m
radio telescope receivers operating in the 41-49 GHz frequency range interfaced
with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz
resolution.
The impedance matching of the cell windows has been studied using different
materials. The choice of the material and its thickness was critical to obtain
a sensitivity identical to that of standard radio astronomical observations.
Spectroscopic signals arising from very low partial pressures of CH3OH,
CH3CH2OH, HCOOH, OCS,CS, SO2 (<1E-03 mbar) were detected in a few seconds. Fast
data acquisition was achieved allowing for kinetic measurements in
fragmentation experiments using electron impact or UV irradiation. Time
evolution of chemical reactions involving OCS, O2 and CS2 was also observed
demonstrating that reactive species, such as CS, can be maintained with high
abundance in the gas phase during these experiments.Comment: Accepted for publication in Astronomy and Astrophysics in September
21, 2017. 16 pages, 18 figure
Multi-wavelength study of the low-luminosity outbursting young star HBC 722
HBC 722 (V2493 Cyg) is a young eruptive star in outburst since 2010. It is an
FU Orionis-type object with an atypically low outburst luminosity. Because it
was well characterized in the pre-outburst phase, HBC 722 is one of the few
FUors where we can learn about the physical changes and processes associated
with the eruption. We monitored the source in the BVRIJHKs bands from the
ground, and at 3.6 and 4.5 m from space with the Spitzer Space Telescope.
We analyzed the light curves and the spectral energy distribution by fitting a
series of steady accretion disk models at many epochs. We also analyzed the
spectral properties of the source based on new optical and infrared spectra. We
also mapped HBC 722 and its surroundings at millimeter wavelengths. From the
light curve analysis we concluded that the first peak of the outburst in 2010
September was due to an abrupt increase of the accretion rate in the innermost
part of the system. This was followed by a long term process, when the
brightening was mainly due to a gradual increase of the accretion rate and the
emitting area. Our new observations show that the source is currently in a
constant plateau phase. We found that around the peak the continuum was bluer
and the H profile changed significantly between 2012 and 2013. The
source was not detected in the millimeter continuum, but we discovered a
flattened molecular gas structure with a diameter of 1700 au and mass of 0.3
M centered on HBC 722. While the first brightness peak could be
interpreted as a rapid fall of piled-up material from the inner disk onto the
star, the later monotonic flux rise suggests the outward expansion of a hot
component according to the theory of Bell & Lin (1994). Our study of HBC 722
demonstrated that accretion-related outbursts can occur in young stellar
objects even with very low mass disks, in the late Class II phase.Comment: 11 pages, 7 figures, 3 online tables. Accepted for publication in the
A&
The IR spectral energy distribution of the Seyfert 2 prototype NGC 5252
The complete mid- to far- infrared continuum energy distribution collected
with the Infrared Space Observatory of the Seyfert 2 prototype NGC 5252 is
presented. ISOCAM images taken in the 3--15 micron range show a resolved
central source that is consistent at all bands with a region of about 1.3 kpc
in size. Due to the lack of on going star formation in the disk of the galaxy,
this resolved emission is associated with either dust heated in the nuclear
active region or with bremsstrahlung emission from the nuclear and extended
ionised gas. The size of the mid-IR emission contrasts with the standard
unification scenario envisaging a compact dusty structure surrounding and
hiding the active nucleus and the broad-line region. The mid-IR data are
complemented with ISOPHOT aperture photometry in the 25--200 micron range. The
overall IR spectral energy distribution is dominated by a well-defined
component peaking at about 100$ micron, a characteristic temperature of T ~20
K, and an associated dust mass of 2.5 x 10E7 Msun, which greatly dominates the
total dust mass content of the galaxy. The heating mechanism of this dust is
probably the interstellar radiation field. After subtracting the contribution
of this cold dust component, the bulk of the residual emission is attributed to
dust heated within the nuclear environment. Its luminosity consistently
accounts for the reprocessing of the X-ray to UV emission derived for the
nucleus of this galaxy. The comparison of NGC 5252 spectral energy distribution
with current torus models favors large nuclear disk structure on the kiloparsec
scale.Comment: 14 pages, 3 figures, to appear in ApJ 583, No.2, 200
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