231 research outputs found
ESA's wind Lidar mission ADM-AEOLUS; on-going scientific activities related to calibration, retrieval and instrument operation
The Earth Explorer Atmospheric Dynamics Mission
(ADM-Aeolus) of ESA will be the first-ever satellite to
provide global observations of wind profiles from
space. Its single payload, namely the Atmospheric
Laser Doppler Instrument (ALADIN) is a directdetection
high spectral resolution Doppler Wind Lidar
(DWL), operating at 355 nm, with a fringe-imaging
receiver (analysing aerosol and cloud backscatter) and a
double-edge receiver (analysing molecular backscatter).
In order to meet the stringent mission requirements on
wind retrieval, ESA is conducting various science
support activities for the consolidation of the on-ground
data processing, calibration and sampling strategies.
Results from a recent laboratory experiment to study
Rayleigh-Brillouin scattering and improve the
characterisation of the molecular lidar backscatter
signal detected by the ALADIN double-edge Fabry-
Perot receiver will be presented in this paper. The
experiment produced the most accurate ever-measured
Rayleigh-Brillouin scattering profiles for a range of
temperature, pressure and gases, representative of
Earth’s atmosphere. The measurements were used to
validate the Tenti S6 model, which is implemented in
the ADM-Aeolus ground processor.
First results from the on-going Vertical Aeolus
Measurement Positioning (VAMP) study will be also
reported. This second study aims at the optimisation of
the ADM-Aeolus vertical sampling in order to
maximise the information content of the retrieved
winds, taking into account the atmospheric dynamical
and optical heterogeneity. The impact of the Aeolus
wind profiles on Numerical Weather Prediction (NWP)
and stratospheric circulation modelling for the different
vertical sampling strategies is also being estimated
Outputs, cost and efficiency of public sector centres for prevention of mother to child transmission of HIV in Andhra Pradesh, India
<p>Abstract</p> <p>Background</p> <p>Prevention of mother to child transmission (PMTCT) is an important part of the effort to control HIV. PMTCT services are mostly provided at public sector government hospitals in India. Systematic data on the cost and efficiency of providing PMTCT services in India are not available readily for further planning.</p> <p>Methods</p> <p>Cost and output data were collected at 16 sampled PMTCT centres in the south Indian state of Andhra Pradesh using standardized methods. The services provided were analysed, and the relation of unit cost of services with scale was assessed.</p> <p>Results</p> <p>In the 2005–2006 fiscal year, 125,073 pregnant women received PMTCT services at the 16 centres (range 2,939 to 20,896, median 5,679). The overall HIV positive rate among those tested was 1.67%. Of the total economic cost, the major components were personnel (47.3%) and recurrent goods (31.7%). For the 16 PMTCT centres, the average economic cost per post-HIV-test counselled pregnant woman was Indian Rupees (INR) 98.9 (US 1.61) to INR 189.9 (US 98) to INR 179,175 (US 231), with very high unit cost at some centres where HIV prevalence among pregnant women and the total volume of services were both low. Scale had a significant inverse relation with both of the unit costs, per post-HIV-test counselled pregnant woman and per mother-neonate pair who received nevirapine. In addition, HIV prevalence among pregnant women had a significant inverse relation with unit cost per mother-neonate pair who received nevirapine.</p> <p>Conclusion</p> <p>Although the variation between PMTCT centres for unit cost per post-HIV-test counselled pregnant woman was modest that per mother-neonate pair receiving nevirapine was over 40-fold. The extremely high unit cost for each mother-neonate pair receiving nevirapine at some centres suggests that the new approach of combining PMTCT services with voluntary counselling and testing services that has recently been started in India could potentially offer better efficiency.</p
Water in massive star-forming regions: HIFI observations of W3 IRS5
We present Herschel observations of the water molecule in the massive
star-forming region W3 IRS5. The o-H17O 110-101, p-H18O 111-000, p-H2O 22
202-111, p-H2O 111-000, o-H2O 221-212, and o-H2O 212-101 lines, covering a
frequency range from 552 up to 1669 GHz, have been detected at high spectral
resolution with HIFI. The water lines in W3 IRS5 show well-defined
high-velocity wings that indicate a clear contribution by outflows. Moreover,
the systematically blue-shifted absorption in the H2O lines suggests expansion,
presumably driven by the outflow. No infall signatures are detected. The p-H2O
111-000 and o-H2O 212-101 lines show absorption from the cold material (T ~ 10
K) in which the high-mass protostellar envelope is embedded. One-dimensional
radiative transfer models are used to estimate water abundances and to further
study the kinematics of the region. We show that the emission in the rare
isotopologues comes directly from the inner parts of the envelope (T > 100 K)
where water ices in the dust mantles evaporate and the gas-phase abundance
increases. The resulting jump in the water abundance (with a constant inner
abundance of 10^{-4}) is needed to reproduce the o-H17O 110-101 and p-H18O
111-000 spectra in our models. We estimate water abundances of 10^{-8} to
10^{-9} in the outer parts of the envelope (T < 100 K). The possibility of two
protostellar objects contributing to the emission is discussed.Comment: Accepted for publication in the A&A HIFI special issu
Water abundances in high-mass protostellar envelopes: Herschel observations with HIFI
We derive the dense core structure and the water abundance in four massive
star-forming regions which may help understand the earliest stages of massive
star formation. We present Herschel-HIFI observations of the para-H2O 1_11-0_00
and 2_02-1_11 and the para-H2-18O 1_11-0_00 transitions. The envelope
contribution to the line profiles is separated from contributions by outflows
and foreground clouds. The envelope contribution is modelled using Monte-Carlo
radiative transfer codes for dust and molecular lines (MC3D and RATRAN), with
the water abundance and the turbulent velocity width as free parameters. While
the outflows are mostly seen in emission in high-J lines, envelopes are seen in
absorption in ground-state lines, which are almost saturated. The derived water
abundances range from 5E-10 to 4E-8 in the outer envelopes. We detect cold
clouds surrounding the protostar envelope, thanks to the very high quality of
the Herschel-HIFI data and the unique ability of water to probe them. Several
foreground clouds are also detected along the line of sight. The low H2O
abundances in massive dense cores are in accordance with the expectation that
high densities and low temperatures lead to freeze-out of water on dust grains.
The spread in abundance values is not clearly linked to physical properties of
the sources.Comment: 8 pages, 5 figures, accepted for publication the 15/07/2010 by
Astronomy&Astrophysics as a letter in the Herschel-HIFI special issu
Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk
We performed a sensitive search for the ground-state emission lines of ortho-
and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI
instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s
channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the
1_{11}--0_{00} line. We report a very tentative detection, however, of the
1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of
T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s.
The latter constitutes a 6sigma detection. Regardless of the reality of this
tentative detection, model calculations indicate that our sensitive limits on
the line strengths preclude efficient desorption of water in the UV illuminated
regions of the disk. We hypothesize that more than 95-99% of the water ice is
locked up in coagulated grains that have settled to the midplane.Comment: 5 pages, 3 figures. Accepted for publication in the Herschel HIFI
special issue of A&
Water in Star-Forming Regions with the Herschel Space Observatory (WISH): Overview of key program and first results
`Water In Star-forming regions with Herschel' (WISH) is a key program on the
Herschel Space Observatory designed to probe the physical and chemical
structure of young stellar objects using water and related molecules and to
follow the water abundance from collapsing clouds to planet-forming disks.
About 80 sources are targeted covering a wide range of luminosities and
evolutionary stages, from cold pre-stellar cores to warm protostellar envelopes
and outflows to disks around young stars. Both the HIFI and PACS instruments
are used to observe a variety of lines of H2O, H218O and chemically related
species. An overview of the scientific motivation and observational strategy of
the program is given together with the modeling approach and analysis tools
that have been developed. Initial science results are presented. These include
a lack of water in cold gas at abundances that are lower than most predictions,
strong water emission from shocks in protostellar environments, the importance
of UV radiation in heating the gas along outflow walls across the full range of
luminosities, and surprisingly widespread detection of the chemically related
hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of
the energy budget indicate that H2O is generally not the dominant coolant in
the warm dense gas associated with protostars. Very deep limits on the cold
gaseous water reservoir in the outer regions of protoplanetary disks are
obtained which have profound implications for our understanding of grain growth
and mixing in disks.Comment: 71 pages, 10 figures, PASP, in pres
HERSCHEL-HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2
HERSCHEL-HIFI observations of water from the intermediate mass protostar
NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this
star formation environment. Six spectral settings, covering four H216O and two
H218O lines, were observed and all but one H218O line were detected. The four
H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6
km/s, component centered slightly redward of the systemic velocity of NGC7129
FIRS 2 and a much broader, \approx 25 km/s component centered blueward and
likely associated with powerful outflows. The narrower components are
consistent with emission from water arising in the envelope around the
intermediate mass protostar, and the abundance of H2O is constrained to \approx
10-7 for the outer envelope. Additionally, the presence of a narrow
self-absorption component for the lowest energy lines is likely due to
self-absorption from colder water in the outer envelope. The broader component,
where the H2O/CO relative abundance is found to be \approx 0.2, appears to be
tracing the same energetic region that produces strong CO emission at high J.Comment: 6 pages, 4 figures, accepted by A&
Hydrides in Young Stellar Objects: Radiation tracers in a protostar-disk-outflow system
Context: Hydrides of the most abundant heavier elements are fundamental
molecules in cosmic chemistry. Some of them trace gas irradiated by UV or
X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a
prototypical region of high-mass star formation. Methods: W3 IRS5 was observed
by HIFI on the Herschel Space Observatory with deep integration (about 2500 s)
in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and
the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines
are found mostly in absorption, but also appear to exhibit weak emission
(P-Cyg-like). Emission requires high density, thus originates most likely near
the protostar. This is corroborated by the absence of line shifts relative to
the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong
absorption components at a velocity shifted relative to W3 IRS5, which are
attributed to foreground clouds. Conclusions: The molecular column densities
derived from observations correlate well with the predictions of a model that
assumes the main emission region is in outflow walls, heated and irradiated by
protostellar UV radiation.Comment: Astronomy and Astrophysics Letters, in pres
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