184 research outputs found
OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS
OH is a key species in the water chemistry of star-forming regions, because
its presence is tightly related to the formation and destruction of water. This
paper presents OH observations from 23 low- and intermediate-mass young stellar
objects obtained with the PACS integral field spectrometer on-board Herschel in
the context of the Water In Star-forming Regions with Herschel (WISH) key
program. Most low-mass sources have compact OH emission (< 5000 AU scale),
whereas the OH lines in most intermediate-mass sources are extended over the
whole PACS detector field-of-view (> 20000 AU). The strength of the OH emission
is correlated with various source properties such as the bolometric luminosity
and the envelope mass, but also with the OI and H2O emission. Rotational
diagrams for sources with many OH lines show that the level populations of OH
can be approximated by a Boltzmann distribution with an excitation temperature
at around 70 K. Radiative transfer models of spherically symmetric envelopes
cannot reproduce the OH emission fluxes nor their broad line widths, strongly
suggesting an outflow origin. Slab excitation models indicate that the observed
excitation temperature can either be reached if the OH molecules are exposed to
a strong far-infrared continuum radiation field or if the gas temperature and
density are sufficiently high. Using realistic source parameters and radiation
fields, it is shown for the case of Ser SMM1 that radiative pumping plays an
important role in transitions arising from upper level energies higher than 300
K. The compact emission in the low-mass sources and the required presence of a
strong radiation field and/or a high density to excite the OH molecules points
towards an origin in shocks in the inner envelope close to the protostar.Comment: Accepted for publication in Astronomy and Astrophysics. Abstract
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High prevalence of urinary schistosomiasis in a desert population: results from an exploratory study around the ounianga lakes in Chad
Background: Researching a water-borne disease in the middle of the Sahara desert might not seem the most relevant concern. However, nomadic Sahelian pastoralist's health concerns regarding their livestock and anecdotal reports about trematode infections of Fasciola spp and Schistosoma spp in desert-raised animals justified an exploratory study focusing on the lakes of Ounianga in Northern Chad. The aim was to test whether trematode parasites such as Schistosoma spp occur in human populations living around the Sahara desert lakes of Ounianga Kebir and Ounianga Saker in northern Chad. Methods: The study comprised of three components. First, a cross sectional survey based on a random sample drawn from the population to detect infections with S. haematobium and S. mansoni ; second, focus group discussions exploring disease priorities, access to health and health seeking behaviour; and third, searching water contact sites for intermediate host snails. Samples of trematode parasites and snails were confirmed on species level by molecular genetics methods. Results: Among 258 participants, the overall S. haematobium prevalence using urine filtration was 39.1% (95% CI 33.2% - 45.1%), with 51.5% of the infected suffering from heavy infection. The intermediate host snail of S. haematobium ( Bulinus truncatus ) occurred at water sites near both study villages, revealing the potential for local transmission. Although a positive S. mansoni POC-CCA test result was obtained from 15.2% (10.6%-19.7%) of the samples no intermediate host snails of S. mansoni were found, and the relevance of S. mansoni remains uncertain. Qualitative findings underline the importance of morbidity caused by urinary schistosomiasis, and the lack of access to diagnostics and treatment as a major health concern. Conclusion: This research revealed a high prevalence of urinary schistosomiasis in the population living around the lakes of Ounianga in the Sahara, a UNESCO world heritage site in Chad. Despite the high public health importance of the associated morbidity expressed by the population there is no access to diagnostics and treatment. Further research is needed to develop and test a context adapted intervention
Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using <i>Herschel</i>-HIFI
Aims. Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin.
Methods. A velocity component with an offset of ~10 kmâs-1 detected in spectra of the H2O 110â101 557 GHz transition towards six low-mass protostars in the âWater in star-forming regions with Herschelâ (WISH) programme is also seen in higher-excited H2O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+, OH) where the same component is uniquely detected.
Results. The velocity component is detected in all six targeted H2O transitions (Eup ~ 50â250 K), as well as in CO 16â15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n ~ 5 Ă 106â108 cm-3) and hot (T ~ 750 K) gas. The H2O and CO column densities are âł1016 and 1018 cm-2, respectively, implying a low H2O abundance of ~10-2 with respect to CO. The high column densities of ions such as OH+ and CH+ (both âł1013 cm-2) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with Trot ~ 700 K is identified as arising in the same component and traces the part of the shock where H2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars
Co-infection of the four major Plasmodium species: effects on densities and gametocyte carriage
BACKGROUND: Co-infection of the four major species of human malaria parasite Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale sp. (Po) is regularly observed, but there is limited understanding of between-species interactions. In particular, little is known about the effects of multiple Plasmodium species co-infections on gametocyte production. METHODS: We developed molecular assays for detecting asexual and gametocyte stages of Pf, Pv, Pm, and Po. This is the first description of molecular diagnostics for Pm and Po gametocytes. These assays were implemented in a unique epidemiological setting in Papua New Guinea with sympatric transmission of all four Plasmodium species permitting a comprehensive investigation of species interactions. FINDINGS: The observed frequency of Pf-Pv co-infection for asexual parasites (14.7%) was higher than expected from individual prevalence rates (23.8%Pf x 47.4%Pv = 11.3%). The observed frequency of co-infection with Pf and Pv gametocytes (4.6%) was higher than expected from individual prevalence rates (13.1%Pf x 28.2%Pv = 3.7%). The excess risk of co-infection was 1.38 (95% confidence interval (CI): 1.09, 1.67) for all parasites and 1.37 (95% CI: 0.95, 1.79) for gametocytes. This excess co-infection risk was partially attributable to malaria infections clustering in some villages. Pf-Pv-Pm triple infections were four times more frequent than expected by chance alone, which could not be fully explained by infections clustering in highly exposed individuals. The effect of co-infection on parasite density was analyzed by systematic comparison of all pairwise interactions. This revealed a significant 6.57-fold increase of Pm density when co-infected with Pf. Pm gametocytemia also increased with Pf co-infection. CONCLUSIONS: Heterogeneity in exposure to mosquitoes is a key epidemiological driver of Plasmodium co-infection. Among the four co-circulating parasites, Pm benefitted most from co-infection with other species. Beyond this, no general prevailing pattern of suppression or facilitation was identified in pairwise analysis of gametocytemia and parasitemia of the four species. TRIAL REGISTRATION: This trial is registered with ClinicalTrials.gov, Trial ID: NCT02143934
Multi-instrument analysis of 67P/Churyumov-Gerasimenko coma particles: COPS-GIADA data fusion
The European Space Agency's Rosetta mission to comet
67P/Churyumov-Gerasimenko has offered scientists the opportunity to study a
comet in unprecedented detail. Four instruments of the Rosetta orbiter, namely,
the Micro-Imaging Dust Analysis System (MIDAS), the Grain Impact Analyzer and
Dust Accumulator (GIADA), the COmetary Secondary Ion Mass Analyser (COSIMA),
and the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) have
provided information on cometary dust particles. Cross-instrument comparisons
are crucial to characterize cometary dust particles beyond the capabilities of
individual sensors, as they are sensitive to different dust components. We
present the first comparison between detections of the ROSINA COmet Pressure
Sensor (COPS) and GIADA. These two instruments are complementary as the former
is sensitive solely to volatiles of icy particles, while the latter measured
the dust particle as a whole, including refractories and condensed
(semi)volatiles. Our goal is to correlate the particles detected by COPS and
GIADA and to assess whether they belong to a common group. We statistically
analyzed the in situ data of COPS and GIADA by calculating Pearson correlation
coefficients. Among the several types of particles detected by GIADA, we find
that COPS particles are significantly correlated solely with GIADA fluffy
agglomerates (Pearson correlation coefficient of 0.55 and p-value of ). This suggests that fluffy particles are composed of both
refractories and volatiles. COPS volatile volumes, which may be represented by
equivalent spheres with a diameter in the range between 0.06 m and 0.8
m, are similar to the sizes of the fractal particle's subunits identified
by MIDAS (i.e., 0.05-0.18 m).Comment: 6 pages, 3 figures, accepted for publication in A&
High-J CO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT
We present and analyze two spectrally resolved high-J CO lines towards the
molecular outflow Cep E, driven by an intermediate-mass class 0 protostar.
Using the GREAT receiver on board SOFIA, we observed the CO (12--11) and
(13--12) transitions (E_u ~ 430 and 500 K, respectively) towards one position
in the blue lobe of this outflow, that had been known to display high-velocity
molecular emission. We detect the outflow emission in both transitions, up to
extremely high velocities (~ 100 km/s with respect to the systemic velocity).
We divide the line profiles into three velocity ranges that each have
interesting spectral features: standard, intermediate, and extremely
high-velocity. One distinct bullet is detected in each of the last two. A large
velocity gradient analysis for these three velocity ranges provides constraints
on the kinetic temperature and volume density of the emitting gas, >~ 100 K and
> ~ 10^4 cm^-3, respectively. These results are in agreement with previous ISO
observations and are comparable with results obtained by Herschel for similar
objects. We conclude that high-J CO lines are a good tracer of molecular
bullets in protostellar outflows. Our analysis suggests that different physical
conditions are at work in the intermediate velocity range compared with the
standard and extremely high-velocity gas at the observed position.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue
Plasmodium vivax and Plasmodium falciparum infection dynamics: re-infections, recrudescences and relapses
Background: In malaria endemic populations, complex patterns of Plasmodium vivax and Plasmodium falciparum blood-stage infection dynamics may be observed. Genotyping samples from longitudinal cohort studies for merozoite surface protein (msp) variants increases the information available in the data, allowing multiple infecting parasite clones in a single individual to be identified. msp genotyped samples from two longitudinal cohorts in Papua New Guinea (PNG) and Thailand were analysed using a statistical model where the times of acquisition and clearance of each clone in every individual were estimated using a process of data augmentation. Results: For the populations analysed, the duration of blood-stage P. falciparum infection was estimated as 36 (95% Credible Interval (CrI): 29, 44) days in PNG, and 135 (95% CrI 94, 191) days in Thailand. Experiments on simulated data indicated that it was not possible to accurately estimate the duration of blood-stage P. vivax infections due to the lack of identifiability between a single blood-stage infection and multiple, sequential blood-stage infections caused by relapses. Despite this limitation, the method and data point towards short duration of blood-stage P. vivax infection with a lower bound of 24 days in PNG, and 29 days in Thailand. On an individual level, P. vivax recurrences cannot be definitively classified into re-infections, recrudescences or relapses, but a probabilistic relapse phenotype can be assigned to each P. vivax sample, allowing investigation of the association between epidemiological covariates and the incidence of relapses. Conclusion: The statistical model developed here provides a useful new tool for in-depth analysis of malaria data from longitudinal cohort studies, and future application to data sets with multi-locus genotyping will allow more detailed investigation of infection dynamics
SOFIA observations of far-infrared hydroxyl emission toward classical ultracompact HII/OH maser regions
The hydroxyl radical (OH) is found in various environments within the
interstellar medium (ISM) of the Milky Way and external galaxies, mostly either
in diffuse interstellar clouds or in the warm, dense environments of newly
formed low-mass and high-mass stars, i.e, in the dense shells of compact and
ultracompact HII regions (UCHIIRs). Until today, most studies of interstellar
OH involved the molecule's radio wavelength hyperfine structure (hfs)
transitions. These lines are generally not in LTE and either masing or
over-cooling complicates their interpretation. In the past, observations of
transitions between different rotational levels of OH, which are at
far-infrared wavelengths, have suffered from limited spectral and angular
resolution. Since these lines have critical densities many orders of magnitude
higher than the radio wavelength ground state hfs lines and are emitted from
levels with more than 100 K above the ground state, when observed in emission,
they probe very dense and warm material. We probe the warm and dense molecular
material surrounding the UCHIIR/OH maser sources W3(OH), G10.62-0.39 and NGC
7538 IRS1 by studying the rotational
transition of OH in emission and, toward the last source also the molecule's
ground-state transition in absorption. We used the
Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe these OH
lines, which are near 1.84 THz (m) and 2.51 THz (m). We
clearly detect the OH lines, some of which are blended with each other.
Employing non-LTE radiative transfer calculations we predict line intensities
using models of a low OH abundance envelope versus a compact, high-abundance
source corresponding to the origin of the radio OH lines.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue
Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using Herschel
Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct
velocity component not seen in observations from the ground of CO or other
species. The aim is to characterise this component in terms of excitation
conditions and physical origin. A velocity component with an offset of ~10 km/s
detected in spectra of the H2O 110-101 557 GHz transition towards six low-mass
protostars in the 'Water in star-forming regions with Herschel' (WISH)
programme is also seen in higher-excited H2O lines. The emission from this
component is quantified and excitation conditions are inferred using 1D slab
models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+,
OH) where the same component is uniquely detected. The velocity component is
detected in all 6 targeted H2O transitions (Eup~50-250K), and in CO 16-15
towards one source, Ser SMM1. Inferred excitation conditions imply that the
emission arises in dense (n~5x10^6-10^8 cm^-3) and hot (T~750K) gas. The H2O
and CO column densities are ~10^16 and 10^18 cm^-2, respectively, implying a
low H2O abundance of 10^-2 with respect to CO. The high column densities of
ions such as OH+ and CH+ (both ~10^13 cm^-2) indicate an origin close to the
protostar where the UV field is strong enough that these species are abundant.
The estimated radius of the emitting region is 100AU. This component likely
arises in dissociative shocks close to the protostar, an interpretation
corroborated by a comparison with models of such shocks. Furthermore, one of
the sources, IRAS4A, shows temporal variability in the offset component over a
period of two years which is expected from shocks in dense media. High-J CO gas
detected with Herschel-PACS with Trot~700K is identified as arising in the same
component and traces the part of the shock where H2 reforms. Thus, H2O reveals
new dynamical components, even on small spatial scales in low-mass protostars.Comment: 13 pages, accepted for publication in A&
OH emission from warm and dense gas in the Orion Bar PDR
As part of a far-infrared (FIR) spectral scan with Herschel/PACS, we present
the first detection of the hydroxyl radical (OH) towards the Orion Bar
photodissociation region (PDR). Five OH rotational Lambda-doublets involving
energy levels out to E_u/k~511 K have been detected (at ~65, ~79, ~84, ~119 and
~163um). The total intensity of the OH lines is I(OH)~5x10^-4 erg s^-1 cm^-2
sr^-1. The observed emission of rotationally excited OH lines is extended and
correlates well with the high-J CO and CH^+ J=3-2 line emission (but apparently
not with water vapour), pointing towards a common origin. Nonlocal, non-LTE
radiative transfer models including excitation by the ambient FIR radiation
field suggest that OH arises in a small filling factor component of warm
(Tk~160-220 K) and dense (n_H~10^{6-7} cm^-3) gas with source-averaged OH
column densities of ~10^15 cm^-2. High density and temperature photochemical
models predict such enhanced OH columns at low depths (A_V<1) and small spatial
scales (~10^15 cm), where OH formation is driven by gas-phase endothermic
reactions of atomic oxygen with molecular hydrogen. We interpret the extended
OH emission as coming from unresolved structures exposed to far-ultraviolet
(FUV) radiation near the Bar edge (photoevaporating clumps or filaments) and
not from the lower density "interclump" medium. Photodissociation leads to
OH/H2O abundance ratios (>1) much higher than those expected in equally warm
regions without enhanced FUV radiation fields.Comment: Accepted for publication in A&A Letters. Figure B.2. is bitmapped to
lower resolutio
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