205 research outputs found
Solenoidal versus compressive turbulence forcing
We analyze the statistics and star formation rate obtained in high-resolution
numerical experiments of forced supersonic turbulence, and compare with
observations. We concentrate on a systematic comparison of solenoidal
(divergence-free) and compressive (curl-free) forcing, which are two limiting
cases of turbulence driving. Our results show that for the same RMS Mach
number, compressive forcing produces a three times larger standard deviation of
the density probability distribution. When self-gravity is included in the
models, the star formation rate is more than one order of magnitude higher for
compressive forcing than for solenoidal forcing.Comment: 1 page, to appear in the proceedings of the IAU General Assembly
Joint Discussion 14 "FIR2009: The ISM of Galaxies in the Far-Infrared and
Sub-Millimetre", ed. M. Cunningha
Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150
To understand the environment and extended structure of the host galactic gas
whose molecular absorption line chemistry, we previously observed along the
microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka
B0355+508), we used the IRAM 30m Telescope and Plateau de Bure Interferometer
to make two series of images of the host gas: i) 22.5 arcsec resolution
single-dish maps of 12CO J=1-0 and 2-1 emission over a 220 arcsec by 220 arcsec
field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of
12CO J=1-0 emission at 5.8 arcsec resolution over a 90 arcsec-diameter region.
CO components that are observed in absorption at a moderate optical depth (0.5)
and are undetected in emission at 1 arcmin resolution toward NRAO 150 remain
undetected at 6 arcsec resolution. This implies that they are not a
previously-hidden large-scale molecular component revealed in absorption, but
they do highlight the robustness of the chemistry into regions where the
density and column density are too low to produce much rotational excitation,
even in CO. Bright CO lines around NRAO150 most probably reflect the variation
of a chemical process, i.e. the C+-CO conversion. However, the ultimate cause
of the variations of this chemical process in such a limited field of view
remains uncertain.Comment: 18 pages, 22 PostScript files giving 14 figures. Accepted for
publication in Astronomy & Astrophysics in the letter section. Uses aa LaTeX
macro
Low sulfur depletion in the Horsehead PDR
We present 3.65''x3.34'' angular-resolution IRAM PdBI observations of the CS
J=2-1 line toward the Horsehead Photodissociation Region (PDR), complemented
with IRAM-30m single-dish observations of several rotational lines of CS, C34S
and HCS+. We analyse the CS and HCS+ photochemistry, excitation and radiative
transfer to obtain their abundances and the physical conditions prevailing in
the cloud edge. Since the CS abundance scales to that of sulfur, we determine
the gas phase sulfur abundance in the PDR, an interesting intermediate medium
between translucent clouds (where sulfur remains in the gas phase) and dark
clouds (where large depletions have been invoked). A nonlocal non-LTE radiative
transfer code including dust and cosmic background illumination adapted to the
Horsehead geometry has been developed to carefuly analyse the CS, C34S, HCS+
and C18O rotational line emission. We use this model to consistently link the
line observations with photochemical models to determine the CS/HCS+/S/S+
structure of the PDR. The combination of CS, C34S and HCS+ observations
together with the inclusion of the most recent CS collisional and chemical
rates in our models implies that sulfur depletion invoked to account for CS and
HCS+ abundances is much smaller than in previous studies.Comment: 20 pages, 17 figures, accepted in A&A, 2006 June 9 (Figs 1 & 4 are
bitmaped
How to manage gait and balance disorders among older adults aged 65 years and older with mild to moderate dementia in clinical practice?
Gait and balance disorders are frequent in demented older adults. Their management (i.e., diagnosis, assessment and treatment) is challenging in daily practice because of numerous evaluation tests available, difficulties to select the most adapted intervention, and the lack of knowledge of physicians and health professionals concerning adapted centers to refer their patients to those patients. Thus, a working group of experts was organized by the Gerontopole of Pays de Loire, France, in December 2010 with the aim to provide clinical guidelines for the management of older adults aged 65 years and older with mild to moderate dementia with gait and balance disorders. These guidelines provide answers to the following questions: 1) Is there gait and/or balance disorders? 2) Which specific tests used? and 3) How to treat patients
CO emission and variable CH and CH+ absorption towards HD34078: evidence for a nascent bow shock ?
The runaway star HD34078, initially selected to investigate small scale
structure in a foreground diffuse cloud has been shown to be surrounded by
highly excited H2. We first search for an association between the foreground
cloud and HD34078. Second, we extend previous investigations of temporal
absorption line variations (CH, CH+, H2) in order to better characterize them.
We have mapped the CO(2-1) emission at 12 arcsec resolution around HD34078's
position, using the 30 m IRAM antenna. The follow-up of CH and CH+ absorption
lines has been extended over 5 more years. In parallel, CH absorption towards
the reddened star Zeta Per have been monitored to check the homogeneity of our
measurements. Three more FUSE spectra have been obtained to search for N(H2)
variations. CO observations show a pronounced maximum near HD34078's position,
clearly indicating that the star and diffuse cloud are associated. The optical
spectra confirm the reality of strong, rapid and correlated CH and CH+
fluctuations. On the other hand, N(H2, J=0) has varied by less than 5 % over 4
years. We also discard N(CH) variations towards Zeta Per at scales less than 20
AU. Observational constraints from this work and from 24 micron dust emission
appear to be consistent with H2 excitation but inconsistent with steady-state
bow shock models and rather suggest that the shell of compressed gas
surrounding HD34078, is seen at an early stage of the interaction. The CH and
CH+ time variations as well as their large abundances are likely due to
chemical structure in the shocked gas layer located at the stellar wind/ambient
cloud interface. Finally, the lack of variations for both N(H2, J=0) towards
HD34078 and N(CH) towards Zeta Per suggests that quiescent molecular gas is not
subject to pronounced small-scale structure.Comment: 19 pages, 15 figures, accepted for publication in A&
Early phase of massive star formation: A case study of Infrared dark cloud G084.81-01.09
We mapped the MSX dark cloud G084.81-01.09 in the NH3 (1,1) - (4,4) lines and
in the J = 1-0 transitions of 12CO, 13CO, C18O and HCO+ in order to study the
physical properties of infrared dark clouds, and to better understand the
initial conditions for massive star formation. Six ammonia cores are identified
with masses ranging from 60 to 250 M_sun, a kinetic temperature of 12 K, and a
molecular hydrogen number density n(H2) ~ 10^5 cm^-3. In our high mass cores,
the ammonia line width of 1 km/s is larger than those found in lower mass cores
but narrower than the more evolved massive ones. We detected self-reversed
profiles in HCO+ across the northern part of our cloud and velocity gradients
in different molecules. These indicate an expanding motion in the outer layer
and more complex motions of the clumps more inside our cloud. We also discuss
the millimeter wave continuum from the dust. These properties indicate that our
cloud is a potential site of massive star formation but is still in a very
early evolutionary stage
Detection of Multiple Variants of Grapevine Fanleaf Virus in Single Xiphinema index Nematodes
Grapevine fanleaf virus (GFLV) is responsible for a widespread disease in vineyards
worldwide. Its genome is composed of two single-stranded positive-sense RNAs, which both show
a high genetic diversity. The virus is transmitted from grapevine to grapevine by the ectoparasitic
nematode Xiphinema index. Grapevines in diseased vineyards are often infected by multiple genetic
variants of GFLV but no information is available on the molecular composition of virus variants
retained in X. index following nematodes feeding on roots. In this work, aviruliferous X. index were
fed on three naturally GFLV-infected grapevines for which the virome was characterized by RNAseq.
Six RNA-1 and four RNA-2 molecules were assembled segregating into four and three distinct
phylogenetic clades of RNA-1 and RNA-2, respectively. After 19 months of rearing, single and pools
of 30 X. index tested positive for GFLV. Additionally, either pooled or single X. index carried multiple
variants of the two GFLV genomic RNAs. However, the full viral genetic diversity found in the leaves
of infected grapevines was not detected in viruliferous nematodes, indicating a genetic bottleneck.
Our results provide new insights into the complexity of GFLV populations and the putative role of X.
index as reservoirs of virus diversity
CCH in prestellar cores
We study the abundance of CCH in prestellar cores both because of its role in
the chemistry and because it is a potential probe of the magnetic field. We
also consider the non-LTE behaviour of the N=1-0 and N=2-1 transitions of CCH
and improve current estimates of the spectroscopic constants of CCH. We used
the IRAM 30m radiotelescope to map the N=1-0 and N=2-1 transitions of CCH
towards the prestellar cores L1498 and CB246. Towards CB246, we also mapped the
1.3 mm dust emission, the J=1-0 transition of N2H+ and the J=2-1 transition of
C18O. We used a Monte Carlo radiative transfer program to analyse the CCH
observations of L1498. We derived the distribution of CCH column densities and
compared with the H2 column densities inferred from dust emission. We find that
while non-LTE intensity ratios of different components of the N=1-0 and N=2-1
lines are present, they are of minor importance and do not impede CCH column
density determinations based upon LTE analysis. Moreover, the comparison of our
Monte-Carlo calculations with observations suggest that the non-LTE deviations
can be qualitatively understood. For L1498, our observations in conjunction
with the Monte Carlo code imply a CCH depletion hole of radius 9 x 10^{16} cm
similar to that found for other C-containing species. We briefly discuss the
significance of the observed CCH abundance distribution. Finally, we used our
observations to provide improved estimates for the rest frequencies of all six
components of the CCH(1-0) line and seven components of CCH(2-1). Based on
these results, we compute improved spectroscopic constants for CCH. We also
give a brief discussion of the prospects for measuring magnetic field strengths
using CCH.Comment: 14 pages, 13 figures, to be published in Astronomy and Astrophysic
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