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Iodine plasmas for space propulsion and industrial applications
No full textInternational audienceWith as many as 2000 satellites per year forecast to be launched over the next decade, onboard propulsion systems will become increasingly important for ensuring both mission success and a sustainable space environment. Plasma-based electric propulsion systems are particularly attractive because of their high fuel efficiency, but due to challenges with conventional propellants such as xenon, a strong interest in viable alternatives has emerged. One such alternative is iodine, which in addition to space-based applications, is also of use in a number of ground-based industrial applications such as plasma etching. With a lower cost, higher global production output, and a reduced ionization threshold compared with xenon, iodine has the potential to meet current and future space industry demand while also providing improved propulsion performance. Furthermore, iodine is a solid at typical ambient conditions with a high storage density. However, iodine is chemically reactive with many common materials and has a more complex plasma chemistry that includes molecular dissociation, attachment to form negative ions, and several ionization processes creating positive atomic and molecular ions. This topical review provides a comprehensive overview of iodine within the context of plasma applications and also serves as a useful data source for various thermodynamic properties, collision cross-sections, and iodine-surface interactions. In addition to discussing the physical and atomic/molecular properties of iodine, we also highlight important theoretical, numerical, and experimental work in the field and discuss the current state-of-the-art: including the space flight heritage of iodine-fueled propulsion systems and remaining research/technical challenges
Shock-driven heating in the circumnuclear star-forming regions of NGC 7582 : insights from JWST NIRSpec and MIRI/MRS spectroscopy
No full textInternational audienceWe present combined James Webb Space Telescope (JWST) NIRSpec and MIRI/MRS integral field spectroscopy data of the nuclear and circumnuclear regions of the highly dust obscured Seyfert 2 galaxy NGC 7582, which is part of the sample of active galactic nucleaus (AGN) in the Galaxy Activity, Torus and Outflow Survey (GATOS). Spatially resolved analysis of the pure rotational H lines (S(1)–S(7)) reveals a characteristic power-law temperature distribution in different apertures, with the two prominent southern star-forming regions exhibiting unexpectedly high molecular gas temperatures, comparable to those in the AGN powered nuclear region. We investigate potential heating mechanisms including direct AGN photoionization, UV fluorescent excitation from young star clusters, and shock excitation. We find that shock heating gives the most plausible explanation, consistent with multiple near- and mid-IR tracers and diagnostics. Using photoionization models from the PhotoDissociation Region Toolbox, we quantify the ISM conditions in the different regions, determining that the southern star-forming regions have a high density ( cm) and are irradiated by a moderate UV radiation field ( Habing). Fitting a suite of Paris-Durham shock models to the rotational H lines, as well as rovibrational 1-0 S(1), 1-0 S(2), and 2-1 S(1) H emission lines, we find that a slow ( km s−1) C-type shock is likely responsible for the elevated temperatures. Our analysis loosely favours local starburst activity as the driver of the shocks and circumnuclear gas dynamics in NGC 7582, though the possibility of an AGN jet contribution cannot be excluded
Observation of the Sr clock transition in a Laguerre-Gaussian Lattice Geometry
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Discovery of new magnetic δ Scuti stars and impact of magnetism on pulsation excitation
No full textInternational audienceContext: At this time, the list of known magnetic δ Scuti stars is extremely limited, with only a handful of well-studied examples.Aims: We seek to expand this list, by retrieving targets from a variety of sources and demonstrating that they present simultaneously a surface magnetic field signature and δ Scuti pulsations. Methods. We obtained archival and new spectropolarimetric datasets for a variety of known δ Scuti stars and analysed them using the Least Squares Deconvolution method to generate mean Stokes I and V profiles for each target, from which we can determine longitudinal magnetic field measurements. Additionally, we assessed photometric data from the TESS satellite to discern frequency peaks consistent with δ Scuti pulsations in known magnetic stars, and to identify magnetic candidates via rotational modulation. Results. We present a compiled list of all the confirmed magnetic δ Scuti stars discovered to date, containing 13 stars. The majority of this sample lies outside the usual δ Scuti instability strip in the H-R diagram, though we do not observe any specific correlations between magnetic field strength and various stellar parameters. This indicates that strong global magnetic fields play a fundamental role in shaping interior structure and processes. Magnetic fields thus must be included in realistic stellar models in order to more accurately predict structure and evolution. Conclusions. This work constitutes the largest database to date of strongly magnetic δ Scuti stars, one that will continue to grow over time with subsequent studies
The X-Point Radiator regime in the WEST tokamak for divertor operation in next step fusion devices
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Evidence of cosmic-ray acceleration up to sub-PeV energies in the supernova remnant IC 443
No full textInternational audienceSupernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain observationally and theoretically, and the role of contribution to CRs around PeV energies by SNRs is unclear. In this study, we present observations of high-energy -ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with -decay signature, and a more extended source which is consistent with a newly discovered source, previously unrecognized by Fermi-LAT. The spectrum of the point source can be described by a power-law function with an index of , extending beyond TeV without apparent cutoff. Assuming a hadronic origin of the -ray emission, the lower limit of accelerated protons reaches about 300 TeV. The extended source might be coincident with IC 443, SNR G189.6+3.3 or the putative pulsar wind nebula CXOU J061705.3+222127, and can be explained by either a hadronic or leptonic model. The LHAASO results provide compelling evidence that CR protons up to sub-PeV energies can be accelerated by the SNR
GW231123: A Binary Black Hole Merger with Total Mass 190–265 M
No full textInternational audienceOn 2023 November 23, the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses 137−18+23M⊙and 101−50+22M⊙(90% credible intervals), at a luminosity distance of 0.7–4.1 Gpc, a redshift of 0.40−0.25+0.27, and with a network signal-to-noise ratio of ∼20.7. Both black holes exhibit high spins—0.90−0.19+0.10and 0.80−0.52+0.20, respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in the inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130 M should be rare, due to pair-instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse and that intermediate-mass black holes of mass ∼200 M form through gravitational-wave-driven mergers
The trans-Neptunian object (119951) 2002 KX14 revealed via multiple stellar occultations
No full textInternational audienceContext. Trans-Neptunian objects (TNOs) are icy bodies located in the outer solar system that offer key insights into the primordial conditions of our planetary system. The stellar occultation technique has proven to be an essential tool for studying these distant and faint objects, enabling precise determinations of their size, shape, and albedo, while also improving estimates of their orbital parameters. Among them, (119951) 2002 KX14 is a large classical TNO with limited previous observations and unresolved questions regarding its physical properties. Aims. This study aims to analyze and characterize the TNO (119951) 2002 KX14 through observations of stellar occultations, providing unique measurements of its size, shape, and albedo. Shape measurements are especially relevant, as only thirteen TNOs have had their projected shapes measured. These results contribute to our understanding of the physical properties of this object and the broader TNO population. Methods. Five stellar occultations by 2002 KX14 were observed from 2020 to 2023, involving multiple telescopes across different locations in Europe and the Americas. High-precision astrometry and photometric data were used to predict the occultation paths and extract ingress and egress timings. One of the events was detected from six sites and there are also several close misses, providing precise constraints for an accurate determination of the object’s limb. Furthermore, elliptical fits to the occultations chords allowed for the determination of the object’s shape and area-equivalent diameter. The geometric albedo was calculated by combining the occultation results with published absolute magnitudes. Results. The five occultations resulted in 15 positive chords that allowed us to accurately measure the shape and size of 2002 KX14. Given that the rotational variability of this body is minimal, we can reasonably assume that the variations are due to albedo features, since the body is classed as a Maclaurin spheroid. The projected ellipse has semi-major and semi-minor axes of 241.0 ± 7.2 km and 157.1 ± 5.2 km, respectively, corresponding to an average area-equivalent diameter of 389.2 ± 8.7 km. The geometric albedo was estimated to be 11.9 ± 0.7%. These values differ from the 455 ± 27 km diameter and the 9.7 -1.3 +1.4 % albedo derived from thermal measurements, offering a more refined understanding of the object’s physical properties