590 research outputs found
Optical performance of the JWST MIRI flight model: characterization of the point spread function at high-resolution
The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard
the James Webb Space Telescope (JWST), providing imaging, coronagraphy and
spectroscopy over the 5-28 microns band. To verify the optical performance of
the instrument, extensive tests were performed at CEA on the flight model (FM)
of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the
infrared. This paper reports on the point spread function (PSF) measurements at
5.6 microns, the shortest operating wavelength for imaging. At 5.6 microns the
PSF is not Nyquist-sampled, so we use am original technique that combines a
microscanning measurement strategy with a deconvolution algorithm to obtain an
over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a
point source on the focal plane. A data inversion method is used to reconstruct
PSF images that are over-resolved by a factor of 7 compared to the native
resolution of MIRI. We show that the FWHM of the high-resolution PSFs were
5-10% wider than that obtained with Zemax simulations. The main cause was
identified as an out-of-specification tilt of the M4 mirror. After correction,
two additional test campaigns were carried out, and we show that the shape of
the PSF is conform to expectations. The FWHM of the PSFs are 0.18-0.20 arcsec,
in agreement with simulations. 56.1-59.2% of the total encircled energy
(normalized to a 5 arcsec radius) is contained within the first dark Airy ring,
over the whole field of view. At longer wavelengths (7.7-25.5 microns), this
percentage is 57-68%. MIRIM is thus compliant with the optical quality
requirements. This characterization of the MIRIM PSF, as well as the
deconvolution method presented here, are of particular importance, not only for
the verification of the optical quality and the MIRI calibration, but also for
scientific applications.Comment: 13 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager
In this article, we describe the MIRI Imager module (MIRIM), which provides
broad-band imaging in the 5 - 27 microns wavelength range for the James Webb
Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed
view of 74"x113". The remainder of its nominal 113"x113" field is occupied by
the coronagraphs and the low resolution spectrometer. We present the instrument
optical and mechanical design. We show that the test data, as measured during
the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton
Laboratory, and at the NASA Goddard Space Flight Center, indicate that the
instrument complies with its design requirements and goals. We also discuss the
operational requirements (multiple dithers and exposures) needed for optimal
scientific utilization of the MIRIM.Comment: 29 pages, 9 figure
Nearby early-type galaxies with ionized gas VI. The Spitzer-IRS view
We present low resolution Spitzer-IRS spectra of 40 ETGs, selected from a
sample of 65 ETGs showing emission lines in their optical spectra. We
homogeneously extract the mid-infrared (MIR) spectra, and after the proper
subtraction of a "passive" ETG template, we derive the intensity of the ionic
and molecular lines and of the polycyclic aromatic hydrocarbon emission
features. We use MIR diagnostic diagrams to investigate the powering mechanisms
of the ionized gas. The mid-infrared spectra of early-type galaxies show a
variety of spectral characteristics. We empirically sub-divide the sample into
five classes of spectra with common characteristics. Class-0, accounting for
20% of the sample, are purely passive ETGs with neither emission lines nor PAH
features. Class-1 show emission lines but no PAH features, and account for
17.5% of the sample. Class-2, in which 50% of the ETGs are found, as well as
having emission lines, show PAH features with unusual ratios, e.g. 7.7
{\mu}m/11.3 {\mu}m \leq 2.3. Class-3 objects have emission lines and PAH
features with ratios typical of star-forming galaxies. 7.5% of objects fall in
this class, likely to be objects in a starburst/post-starburst regime. Class-4,
containing only 5% of the ETGs, is dominated by a hot dust continuum. The
diagnostic diagram [Ne III]15.55{\mu}m/[Ne II]12.8{\mu}m vs. [S
III]33.48{\mu}m/[Si II]34.82{\mu}m, is used to investigate the different
mechanisms ionizing the gas. If we exclude NGC 3258 where a starburst seems
present, most of our ETGs contain gas ionized via either AGN-like or shock
phenomena, or both. Most of the spectra in the present sample are classified as
LINERs in the optical window. The proposed MIR spectral classes show
unambiguously the manifold of the physical processes and ionization mechanisms,
from star formation, low level AGN activity, to shocks, present in LINER
nuclei.Comment: Accepted for publication in Astronomy and Astrophysic
3-D Ultrastructure of O. tauri: Electron Cryotomography of an Entire Eukaryotic Cell
The hallmark of eukaryotic cells is their segregation of key biological functions into discrete, membrane-bound organelles. Creating accurate models of their ultrastructural complexity has been difficult in part because of the limited resolution of light microscopy and the artifact-prone nature of conventional electron microscopy. Here we explored the potential of the emerging technology electron cryotomography to produce three-dimensional images of an entire eukaryotic cell in a near-native state. Ostreococcus tauri was chosen as the specimen because as a unicellular picoplankton with just one copy of each organelle, it is the smallest known eukaryote and was therefore likely to yield the highest resolution images. Whole cells were imaged at various stages of the cell cycle, yielding 3-D reconstructions of complete chloroplasts, mitochondria, endoplasmic reticula, Golgi bodies, peroxisomes, microtubules, and putative ribosome distributions in-situ. Surprisingly, the nucleus was seen to open long before mitosis, and while one microtubule (or two in some predivisional cells) was consistently present, no mitotic spindle was ever observed, prompting speculation that a single microtubule might be sufficient to segregate multiple chromosomes
Very early MRI responses to therapy as a predictor of later radiographic progression in early rheumatoid arthritis
Background:
The objective of this study was to evaluate early changes in magnetic resonance imaging (MRI) and clinical disease activity measures as predictors of later structural progression in early rheumatoid arthritis (RA).
Methods:
This was a post hoc analysis of data pooled across treatments from a three-arm (tofacitinib monotherapy, tofacitinib with methotrexate [MTX], or MTX monotherapy) trial of MTX-naïve patients with early, active RA. Synovitis, osteitis and erosions were assessed with the Outcome Measures in Rheumatology (OMERACT) RA MRI scoring system (RAMRIS) and RAMRIQ (automated quantitative RA MRI assessment system; automated RAMRIS) at months 0, 1, 3, 6 and 12. Radiographs were assessed at months 0, 6 and 12, and clinical endpoints were assessed at all timepoints. Univariate and multivariate analyses explored the predictive value of early changes in RAMRIS/RAMRIQ parameters and disease activity measures, with respect to subsequent radiographic progression.
Results:
Data from 109 patients with a mean RA duration of 0.7 years were included. In univariate analyses, changes in RAMRIS erosions at months 1 and 3 significantly predicted radiographic progression at month 12 (both p < 0.01); changes in RAMRIQ synovitis and osteitis at months 1 and 3 were significant predictors of RAMRIS erosions and radiographic progression at month 12 (all p < 0.01). In subsequent multivariate analyses, RAMRIS erosion change at month 1 (p < 0.05) and RAMRIQ osteitis changes at months 1 and 3 (both p < 0.01) were significant independent predictors of radiographic progression at month 12. Univariate analyses demonstrated that changes in Clinical Disease Activity Index (CDAI) and Disease Activity Score in 28 joints, erythrocyte sedimentation rate (DAS28-4[ESR]) at months 1 and 3 were not predictive of month 12 radiographic progression.
Conclusions:
MRI changes seen as early as 1 month after RA treatment initiation have the potential to better predict long-term radiographic progression than changes in disease activity measures.
Trial registration:
ClinicalTrials.gov, NCT01164579
Observations of the planetary nebula SMP LMC 058 with the JWST MIRI medium resolution spectrometer
During the commissioning of JWST, the medium-resolution spectrometer (MRS) on the mid-infrared instrument (MIRI) observed the planetary nebula SMP LMC 058 in the Large Magellanic Cloud. The MRS was designed to provide medium resolution (R = λ/Δλ) 3D spectroscopy in the whole MIRI range. SMP LMC 058 is the only source observed in JWST commissioning that is both spatially and spectrally unresolved by the MRS and is a good test of JWST's capabilities. The new MRS spectra reveal a wealth of emission lines not previously detected in this planetary nebula. From these lines, the spectral resolving power (λ/Δλ) of the MRS is confirmed to be in the range R = 4000-1500, depending on the MRS spectral sub-band. In addition, the spectra confirm that the carbon-rich dust emission is from complex hydrocarbons and SiC grains and that there is little to no time evolution of the SiC dust and emission line strengths over a 17-yr epoch. These commissioning data reveal the great potential of the MIRI MRS for the study of circumstellar and interstellar material.</p
Nuclear high-ionisation outflow in the Compton-thick AGN NGC6552 as seen by the JWST mid-infrared instrument
During the commissioning of the James Webb Space Telescope (JWST), the
mid-infrared instrument (MIRI) observed NGC6552 with the MIRI Imager and the
medium-resolution spectrograph (MRS). NGC6552 is an active galactic nucleus
(AGN) at redshift 0.0266 classified as a Seyfert 2 nucleus in the optical, and
Compton-thick AGN in X-rays. This work exemplifies and demonstrates the MRS
capabilities to study the mid-infrared (mid-IR) spectra and characterize the
physical conditions and kinematics of the ionized and molecular gas in the
nuclear regions of nearby galaxies. We obtained the nuclear, circumnuclear, and
central mid-IR spectra of NGC6552. They provide the first clear observational
evidence for a nuclear outflow in NGC6552. The outflow contributes to 677%
of the total line flux independent of the ionization potential (27 to 187 eV)
and critical densities (10 to 410 cm), showing an
average blue-shifted peak velocity of -12745 kms and an outflow
maximal velocity of 69880 kms. Since the mid-IR photons penetrate
dusty regions as efficiently as X-ray keV photons, we interpret these results
as the evidence for a highly ionized, non-stratified, AGN-powered, and fast
outflowing gas in a low density environment (few 10 cm) located
very close (<0.2kpc) to the Compton-thick AGN. Nine pure rotational molecular
Hydrogen lines are detected and spectrally resolved, and exhibit symmetric
Gaussian profiles, consistent with the galactic rotation, and with no evidence
of outflowing H material. We detect a warm H mass of
in the central region (1.8 kpc in diameter) of
the galaxy, with almost 30% of that mass in the circum-nuclear region. Line
ratios confirm that NGC6552 has a Seyfert nucleus with a black hole mass
estimated in the range of 0.6 to 6 million solar masses.Comment: 13 pages, 5 figures, 5 tables, accepted in A&
Shock-enhanced C+ emission and the detection of H2O from the Stephan’s Quintet group-wide shock using Herschel
WWe present the first Herschelspectroscopic detections of the [O i] 63 μm and [Cii] 158 μm fine-structure transitions, and a single para-H2O line from the 35 × 15 kpc2 shocked intergalactic filament in Stephan’s Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with a clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (>1000 km s−1) luminous [Cii] line profiles, as well as fainter [O i] 63 μm emission. SPIRE FTS observations reveal water emission from the p-H2O (111–000) transition at several positions in the filament, but no other molecular lines. The H2O line is narrow and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [Cii]/PAHtot and [C ii]/FIR ratios are too large to be explained by normal photo-electric heating in photodissociation regions. H ii region excitation or X-ray/cosmic-ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [Cii], [O i], and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the intergalactic medium is dissipated to small scales and low velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [Cii]/[O i] ratio, and the relatively high [C ii]/H2 ratios observed. The discovery that [Cii] emission can be enhanced, in large-scale turbulent regions in collisional environments, has implications for the interpretation of [C ii] emission in high-z galaxies
High CO2 and Silicate Limitation Synergistically Increase the Toxicity of Pseudo-nitzschia fraudulenta
Anthropogenic CO2 is progressively acidifying the ocean, but the responses of harmful algal bloom species that produce toxins that can bioaccumulate remain virtually unknown. The neurotoxin domoic acid is produced by the globally-distributed diatom genus Pseudo-nitzschia. This toxin is responsible for amnesic shellfish poisoning, which can result in illness or death in humans and regularly causes mass mortalities of marine mammals and birds. Domoic acid production by Pseudo-nitzschia cells is known to be regulated by nutrient availability, but potential interactions with increasing seawater CO2 concentrations are poorly understood. Here we present experiments measuring domoic acid production by acclimatized cultures of Pseudo-nitzschia fraudulenta that demonstrate a strong synergism between projected future CO2 levels (765 ppm) and silicate-limited growth, which greatly increases cellular toxicity relative to growth under modern atmospheric (360 ppm) or pre-industrial (200 ppm) CO2 conditions. Cellular Si∶C ratios decrease with increasing CO2, in a trend opposite to that seen for domoic acid production. The coastal California upwelling system where this species was isolated currently exhibits rapidly increasing levels of anthropogenic acidification, as well as widespread episodic silicate limitation of diatom growth. Our results suggest that the current ecosystem and human health impacts of toxic Pseudo-nitzschia blooms could be greatly exacerbated by future ocean acidification and ‘carbon fertilization’ of the coastal ocean
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