165 research outputs found
Indigenous research protocols: [Gatekeepers, guardians and gatecrashers]
No full textProtocols are about rules and relationships. The title of Dr Miri Raven’s talk is that of her PhD, which looked at the enactment of protocols to protect Indigenous knowledge and how protocols order these practices. Dr Raven will discuss what Indigenous research protocols are and how they operate in practice. It will provide an opportunity for researchers to reflect on their own practices when working with Indigenous communities and organisations
The brighter-fatter effect in the JWST MIRI Si:As IBC detectors I. Observations, impact on science, and modeling
No full textContext. The Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) uses three Si:As impurity band conduction (IBC) detector arrays. The output voltage level of each MIRI detector pixel is digitally recorded by sampling up the ramp. For uniform or low-contrast illumination, the pixel ramps become nonlinear in a predictable way, but in areas of high contrast, the nonlinearity curve becomes much more complex. The origin of the effect is poorly understood and currently not calibrated out of the data. Aims. We provide observational evidence of the brighter-fatter effect (BFE) in MIRI conventional and high-contrast coronagraphic imaging, low-resolution spectroscopy, and medium-resolution spectroscopy data, and we investigate the physical mechanism that gives rise to the effect on the MIRI detector pixel raw voltage integration ramps. Methods. We used public data from the JWST/MIRI commissioning and Cycle 1 phase. We also developed a numerical electrostatic model of the MIRI detectors using a modified version of the public Poisson_CCD code. Results. We find that the physical mechanism behind the BFE manifesting in MIRI data is fundamentally different to that of chargecoupled devices and photodiode arrays such as the Hawaii-XRG near-infrared detectors used by the NIRISS, NIRCam, and NIRSpec instruments on board JWST. Observationally, the BFE makes the JWST MIRI data yield 10-25% larger point sources and spectral line profiles as a function of the relative level of de-biasing of neighboring detector pixels. This broadening impacts the MIRI absolute flux calibration, time-series observations of faint companions, and point spread function modeling and subtraction. We also find that the intra-pixel 2D profile of the shrinking Si:As IBC detector depletion region directly impacts the accuracy of the pixel ramp nonlinearity calibration model.Planetary Exploratio
Wavelength calibration and resolving power of the JWST MIRI Medium Resolution Spectrometer
No full textContext. The Mid-Infrared Instrument (MIRI) onboard the James Webb Space Telescope (JWST) will provide imaging, coronagraphy, low-resolution spectroscopy, and medium-resolution spectroscopy at unprecedented sensitivity levels in the mid-infrared wavelength range. The Medium Resolution Spectrometer (MRS) of MIRI is an integral field spectrograph that provides diffraction-limited spectroscopy between 4.9 and 28.3 μm, within a field of view (FOV) varying from ∼13 to ∼56 arcsec square. The design for MIRI MRS conforms with the goals of the JWST mission to observe high redshift galaxies and to study cosmology as well as observations of galactic objects, and stellar and planetary systems. Aims. From ground testing, we calculate the physical parameters essential for general observers and calibrating the wavelength solution and resolving power of the MRS which is critical for maximizing the scientific performance of the instrument. Methods. We have used ground-based observations of discrete spectral features in combination with Fabry-Perot etalon spectra to characterize the wavelength solution and spectral resolving power of the MRS. We present the methodology used to derive the MRS spectral characterization, which includes the precise wavelength coverage of each MRS sub-band, computation of the resolving power as a function of wavelength, and measuring slice-dependent spectral distortions. Results. The ground calibration of the MRS shows that it will cover the wavelength ranges from 4.9 to 28.3 μm, divided in 12 overlapping spectral sub-bands. The resolving power is R 3500 in channel 1, R 3000 in channel 2, R 2500 in channel 3, and R 1500 in channel 4. The MRS spectral resolution optimizes the sensitivity for detection of spectral features with a velocity width of ∼100 km s-1 which is characteristic of most astronomical phenomena JWST aims to study in the mid-infrared. Based on the ground test data, the wavelength calibration accuracy is estimated to be below one-tenth of a pixel (0.1 nm at 5 μm and 0.4 at 28 μm), with small systematic shifts due to the target position within a slice for unresolved sources that have a maximum amplitude of about 0.25 spectral resolution elements. The absolute wavelength calibration is presently uncertain at the level of 0.35 nm at 5 μm and 46 nm at 28 μm, and it will be refined using in-flight commissioning observations. Conclusions. Based on ground test data, the MRS complies with the spectral requirements for both the R and wavelength accuracy for which it was designed. We also present the commissioning strategies and targets that will be followed to update the spectral characterization of the MRS. Accepted Author ManuscriptAstrodynamics & Space Mission
Performing the Author
No full textchs wird in seinem Aufbau durch die drei Phasen des Selbstfindungsprozesses, genauer der Selbsterfindung der ‚Schriftstellerin Yū Miri‘ in ihren Werken und ihren medialen Selbstinszenierungen strukturiert. Es gelingt Iwata-Weickgenannt sehr überzeugend, das Sichtbarmachen der performativen Konstruiertheit von Identität im Werk und Leben Yūs herauszuarbeiten. Sie zeigt dabei auch, dass das Konzept der Performativität ein sehr geeigneter Bezugsrahmen für die Analyse von Identitätsbildungsprozessen ist.The Japanese-Korean author Yū Miri (born in 1968), still fairly unknown in Germany, belongs to those successful contemporary Japanese authors for whom it is typical to be known and celebrated not only for their texts but also for their excessive media presence. The multimedia staging by the author of her self as the ‘author Yū Miri’ sparks just as much interest in the Japanese public and literary scene as do her literary texts. In her book, published by the Munich-based house Iudicium Verlag, Iwata-Weickgenannt provides not only a comprehensive overview of Yū’s literary works published between the years of 1994 and 2005, but she also thematizes the medial representation of ‘Yū Miri’ in her analyses. In the first section of her book, Iwata-Weickgenannt provides a very good overview of the field out of which Yū’s identity problematic as a Japanese-Korean author arises. The second main section of the book is structured along the three phases of the self-discovery process, or rather the self-creation process, o
JWST MIRI Flight Performance: Detector Effects and Data Reduction Algorithms
No full textThe detectors in the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST) are arsenic-doped silicon impurity band conduction (Si:As IBC) devices and are direct descendants of the Spitzer IRAC long wavelength arrays (channels 3 and 4). With appropriate data processing, they can provide excellent performance. In this paper we discuss the various non-ideal behaviors of these detectors that need to be addressed to realize their potential. We have developed a set of algorithms toward this goal, building on experience with previous similar detector arrays. The MIRI-specific stage 1 pipeline algorithms, of a three stage JWST calibration pipeline, were developed using pre-flight tests on the flight detectors and flight spares and have been refined using flight data. This paper describes these algorithms, which are included in the first stage of the JWST Calibration Pipeline for the MIRI instrument. © 2023. The Author(s). Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP). All rights reserved.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
In conversation with Geographers, Regenerative futures
No full textFor the first webinar of 2022, we welcomed Miri Raven [UNSW], Jason Prior [UTS], Kristian Ruming {Macquarie], Jason Byrne [UTAS], and Philipa Duthie [RSA Oceania]. Together they explored a report, published in October 2021, by Josie Warden from the Royal Society of Arts. The paper is entitled 'Regenerative Futures. From sustaining to thriving together'. In it, Warden considered the meaning of the term regenerative, shared varied perspectives on the term, outlined the ways in which it signifies living systems perspectives, invited readers to think deeply about questions related to the future, and described eight guiding principles for regenerative design. Geographers surely will have much to contribute to the ways in which these principles are made manifest, and this webinar heard views from several leading members of the discipline
GATOS – IX. A detailed assessment and treatment of emission line contamination in JWST/MIRI images of nearby Seyfert galaxies
Full text link\ua9 The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society.Broad-band mid-infrared (MIR) imaging with high-spatial resolution is useful to study extended dust structures in the circumnuclear regions of nearby active galactic nuclei. However, broad-band imaging filters cannot distinguish dust continuum emission from emission lines, and so accounting for the emission line contamination becomes crucial in studying extended dust in these environments. This paper uses Cycle 1 MIR imaging from the James Webb Space Telescope\u27s Mid-Infrared Instrument (JWST/MIRI) and spectroscopy from the Medium-Resolution Spectrometer (JWST/MRS) for 11 local Seyfert galaxies, as part of the Galactic Activity, Torus and Outflow Survey (GATOS). Three of the objects (NGC 3081, NGC 5728, and NGC 7172) exist in both data sets, allowing direct measurement of the line emission using the spectroscopy for these objects. We find that extended MIR emission persists on scales of 100 s of parsecs after the removal of contamination from emission lines. Further, the line contamination levels vary greatly between objects (from 5 percent to 30 percent in the F1000W filter), and across filters, so cannot be generalized across a sample and must be carefully treated for each object and band. We also test methods to estimate the line contamination when only MRS spectroscopy or MIRI imaging is available, using pre-JWST ancillary data. We find that these methods estimate the contamination within 10 percentage points. This paper serves as a useful guide for methods to quantify and mitigate for emission line contamination in MIRI broad-band imaging
Nuclear high-ionisation outflow in the Compton-thick AGN NGC 6552 as seen by the JWST mid-infrared instrument
No full textContext. During the commissioning of the James Webb Space Telescope (JWST), the mid-infrared instrument (MIRI) observed NGC 6552 with the MIRI Imager and the Medium-Resolution Spectrograph (MRS). NGC 6552 is an active galactic nucleus (AGN) at a redshift of 0.0266 (DL = 120 Mpc) classified as a Seyfert 2 nucleus in the optical and Compton-thick AGN in the X-ray. Aims. This work exemplifies and demonstrates the MRS capabilities to study the mid-infrared (mid-IR) spectra and characterise the physical conditions and kinematics of the ionised and molecular gas in the nuclear regions of nearby galaxies. Methods. MIRI Imager observations covers the full NGC 6552 galaxy at 5.6 μm. MRS observations covers its nuclear region (3.6 × 4.3 kpc at 17.7-27.9 μm) in a wavelength range between 4.9 and 27.9 μm. These observations were obtained with the aim to investigate the persistence of the MIRI detectors (residual signal left from previous bright source observations). However, NGC 6552 observations demonstrate the performance and power of the MIRI instrument even with a non-optimal observational strategy. Results. We obtained the nuclear, circumnuclear, and central mid-IR spectra of NGC 6552. They provide the first clear observational evidence for a nuclear outflow in NGC 6552. The outflow contributes to 67±7% of the total line flux independent of the ionisation potential (27-187 eV) and critical densities (104-4 × 106 cm-3), showing an average blue-shifted peak velocity of -127±45 km s-1 and an outflow maximal velocity of 698±80 km s-1. 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 ionised, non-stratified, AGN-powered, and fast outflowing gas in a low density environment (few 103 cm-3) located very close (< 0.2 kpc) 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 H2 material. We detect a warm H2 mass of 1.9 ± 1.1 × 107 M⊙ in the central region (1.8 kpc in diameter) of the galaxy, with almost 30% of that mass in the circumnuclear region. Line ratios confirm that NGC 6552 has a Seyfert nucleus with a black hole mass estimated in the range of 0.6-6 million solar masses. Conclusions. This work demonstrates the power of the newly commissioned MIRI Medium Resolution Spectrograph to reveal new insights in the kinematics and ionisation state of the interstellar medium around the dusty nuclear regions of nearby active galaxies. Astrodynamics & Space Mission
Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations
No full textContext. We present the first spectroscopic observations of Ganymede by the James Webb Space Telescope undertaken in August 2022 as part of the proposal "ERS observations of the Jovian system as a demonstration of JWST's capabilities for Solar System science". Aims. We aimed to investigate the composition and thermal properties of the surface, and to study the relationships of ice and non-water-ice materials and their distribution. Methods. NIRSpec IFU (2.9-5.3 μm) and MIRI MRS (4.9-28.5 μm) observations were performed on both the leading and trailing hemispheres of Ganymede, with a spectral resolution of ∼2700 and a spatial sampling of 0.1 to 0.17″ (while the Ganymede size was ∼1.68″). We characterized the spectral signatures and their spatial distribution on the surface. The distribution of brightness temperatures was analyzed with standard thermophysical modeling including surface roughness. Results. Reflectance spectra show signatures of water ice, CO2, and H2O2. An absorption feature at 5.9 μm, with a shoulder at 6.5 μm, is revealed, and is tentatively assigned to sulfuric acid hydrates. The CO2 4.26-μm band shows latitudinal and longitudinal variations in depth, shape, and position over the two hemispheres, unveiling different CO2 physical states. In the ice-rich polar regions, which are the most exposed to Jupiter's plasma irradiation, the CO2 band is redshifted with respect to other terrains. In the boreal region of the leading hemisphere, the CO2 band is dominated by a high wavelength component at ∼4.27 μm, consistent with CO2 trapped in amorphous water ice. At equatorial latitudes (and especially on dark terrains), the observed band is broader and shifted toward the blue, suggesting CO2 adsorbed on non-icy materials, such as minerals or salts. Maps of the H2O Fresnel peak area correlate with Bond albedo maps and follow the distribution of water ice inferred from H2O absorption bands. Amorphous ice is detected in the ice-rich polar regions, and is especially abundant on the northern polar cap of the leading hemisphere. Leading and trailing polar regions exhibit different H2O, CO2, and H2O2 spectral properties. However, in both hemispheres the north polar cap ice appears to be more processed than the south polar cap. A longitudinal modification of the H2O ice molecular structure and/or nanometer- and micrometer-scale texture, of diurnal or geographic origin, is observed in both hemispheres. Ice frost is tentatively observed on the morning limb of the trailing hemisphere, which possibly formed during the night from the recondensation of water subliming from the warmer subsurface. Reflectance spectra of the dark terrains are compatible with the presence of Na- and Mg-sulfate salts, sulfuric acid hydrates, and possibly phyllosilicates mixed with fine-grained opaque minerals, with a highly porous texture. Latitude and local time variations of the brightness temperatures indicate a rough surface with mean slope angles of 15° - 25° and a low thermal inertia Γ = 20-40 J m-2 s-0.5 K-1, consistent with a porous surface, with no obvious difference between the leading and trailing sides.Planetary ExplorationAstrodynamics & Space Mission
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