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Investigation of Filamentary and Diffuse DBD in CO<sub>2</sub> by Means of InSitu FTIR Absorption Spectroscopy
No full textInternational audienceThis work investigates CO2 dielectric barrier discharges (DBDs) at atmospheric pressure in the filamentary and diffuse regimes for the first time using in situ FTIR absorption measurements. The conversion factor of CO2 is determined and is consistent with the results obtained for DBDs in the literature, following a power law with respect to the specific energy input in both regimes. Vibrational temperatures for CO2 and CO molecules as well as rotational temperature are also determined within the discharge. A noticeably high vibrational temperature of CO is observed for low specific energy input (SEI). It drops abruptly when increasing the SEI which is attributed to strong vibrationalto-translational energy transfers by O atoms coming from CO2 dissociation. Except that, the ordering of the different temperatures is similar to the results reported for other CO2 discharges generated at lower pressures: the vibrational temperature of CO is higher than those of the different vibrational modes of CO2. The latter are slightly higher than the rotational temperature of the gas for the diffuse mode, whereas they are almost the same for the filamentary mode. The evolution of the measured parameters as a function of the specific energy input is then discussed and a detailed comparison of the two different regimes is carried out. These data together with the knowledge of the reduced electric field in the diffuse regime, which is included in the range 120-140 Td for all conditions, can be of significant importance for further studies exploring the fundamentals of CO2 plasma chemistry at atmospheric pressure, serving as reference for kinetic models
Capture and escape from the 2:1 resonance between Ariel and Umbriel in a fast-migration scenario of the Uranian system
No full textInternational audienceRecent measurements suggest that Uranus may exhibit a higher tidaldissipation than previously assumed. This enhanced dissipation leads to afaster orbital migration of its five major moons: Miranda, Ariel, Umbriel,Titania, and Oberon. Consequently, resonant encounters that have always beendiscarded in previous works need to be included. In particular, Ariel's fastmigration implies that the crossing of the 2:1 mean motion resonance withUmbriel is extremely likely and it could have occurred in recent times. Captureinto this strong resonance would have induced significant tidal heating withinAriel, possibly explaining its resurfacing. Therefore, in this work, we aim toexplore the orbital history of the Uranian moons in a context of fast tidalmigration, including the crossing of the 2:1 mean motion resonance betweenAriel and Umbriel. For small initial eccentricities, we confirm that the moonsare always captured into this resonance. As the system is not currentlyinvolved in any mean motion resonance, we investigated possible dynamicalmechanisms for exiting the 2:1 resonance. We show that the resonance could havebeen broken by a further resonant encounter with Titania. We analyzed thecrossing of the 4:2:1 and 3:2:1 resonant chains, and looked for the parameterspace where the probability of escaping the resonance is maximized. Taking adissipative parameter of Ariel k_{2,2}/Q_2<10^{-3}, the passage through the3:2:1 resonance succeeds in disrupting the 2:1 Ariel-Umbriel mean motionresonance in more than of our numerical experiments. A fraction of oursimulations results in final low eccentricities and inclinations, which caneventually match the current orbital features of the system. As the proposedorbital history requires specific ranges of the dissipative parameters for thesystem, future Uranus mission data will validate (or disprove) this scenario
The quest for habitats in the outer Solar System and how to protect exotic pristine environments
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Orbit and atmosphere of HIP 99770 b through the eyes of VLTI/GRAVITY
No full textInternational audienceContext . Inferring the likely formation channel of giant exoplanets and brown dwarf companions from orbital and atmospheric observables remains a formidable challenge. Further and more precise directly measured dynamical masses of these companions are required to inform and gauge formation, evolutionary, and atmospheric models. We present an updated study of the recently discovered companion to HIP 99770 based on observations conducted with the near-infrared interferometer VLTI/GRAVITY. Aims . Through renewed orbital and spectral analyses based on the GRAVITY data, we characterise HIP 99770 b to better constrain its orbit, dynamical mass, and atmospheric properties, as well as to shed light on its likely formation channel. Methods . Upon inclusion of the new high-precision astrometry epoch, we ran an orbit fit to further constrain the dynamical mass of the companion and the orbit solution. We also analysed the GRAVITY K-band spectrum, placing it into context with literature data, and extracting magnitude, age, spectral type, bulk properties and atmospheric characteristics of HIP 99770 b. Results . We detected the companion at a radial separation of 417 mas from its host. The new orbit fit yields a dynamical mass of 17 −5 +6 M Jup and an eccentricity of 0.31 −0.12 +0.06 . We also find that additional relative astrometry epochs in the future will not enable further constraints on the dynamical mass due to the dominating relative uncertainty on the Hipparcos- Gaia proper motion anomaly that is used in the orbit-fitting routine. The publication of Gaia DR4 will likely ease this predicament. Based on the spectral analysis, we find that the companion is consistent with spectral type L8 and exhibits a potential metal enrichment in its atmosphere. Adopting the AMES-DUSTY model to infer its age, within its dynamical mass constraint the companion conceivably corresponds to either a younger (28 −14 +15 Myr) object with a mass just below the deuterium-burning limit or an older (119 −10 +37 Myr) body with a mass just above the deuterium-burning limit. Conclusions . These results do not yet allow for a definite inference of the companion’s formation channel. Nevertheless, the new constraints on its bulk properties and the additional GRAVITY spectrum presented here will aid future efforts to determine the formation history of HIP 99770 b
Search for Diffuse Galactic Neutrinos with the Full ANTARES Telescope Dataset
No full textInternational audienceThe diffuse emission of gamma-rays and neutrinos, produced by interactions of cosmic rays with interstellar matter in the Milky Way, provides valuable insights into cosmic ray propagation and Galactic processes. Emission models incorporating different assumptions about cosmic ray diffusion, source distribution, and target gas density are tested using data from neutrino telescopes. In this study, the final all-flavor neutrino dataset, collected over 15 years (2007--2022) by the ANTARES neutrino telescope, is analyzed. A maximum likelihood ratio method built to handle templates of Galactic emission models is employed to evaluate the compatibility of these models with the observed spatial and energy distributions of neutrino events. The results do not yield stringent constraints on the tested models and upper limits on the diffuse neutrino flux are derived, which are compatible with the results obtained by other experiments
The most distant optically polarised GRB afterglow: GRB 240419A at z = 5.178
No full textInternational audienceGamma-ray bursts (GRBs) are extremely bright phenomena powered by relativistic jets arising from explosive events at cosmological distances. The nature of the jet and the configuration of the local magnetic fields are still unclear, with the distinction between different models possibly provided by the detection of early-time polarisation. Past observations do not agree on a universal scenario describing early-time polarisation in GRB afterglows, and new studies are necessary to investigate this open question. We present here the discovery of GRB 240419A, its redshift determination of , its early-time optical polarimetry observations, and the multi-wavelength monitoring of its afterglow. We analysed three epochs of polarimetric data to derive the early-time evolution of the polarisation. The multi-wavelength light curve from the X-rays to the near-infrared band was also investigated to give a broader perspective on the whole event. We find a high level of polarisation, %, at 1740~s after the GRB trigger, followed by a slight decrease up to % at 3059~s. On the same timescale, the polarisation position angle is nearly constant. The multi-band afterglow at the time of the polarisation measurements is consistent with a forward shock (FS), while the earlier evolution at s can be associated with the interplay between the forward and the reverse shocks or with energy injection. The detected polarised radiation when the afterglow is FS-dominated and the stable position angle are consistent with an ordered magnetic field plus a turbulent component driven by large-scale magnetohydrodynamic instabilities. The lack of a jet break in the light curve prevents a comparison of the polarisation temporal evolution with theoretical expectations from magnetic fields amplified by microscopic-scale turbulence, limiting ..
Erratum: "First absolute wind measurements in Saturn's stratosphere from ALMA observations"
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H i Properties of Field Galaxies at z ≈ 0.2–0.6: Insights into Declining Cosmic Star Formation
No full textInternational audienceAbstract We report statistically significant detection of H i 21 cm emission from intermediate-redshift ( z ≈ 0.2–0.6) galaxies. By leveraging multisightline galaxy survey data from the Cosmic Ultraviolet Baryon Survey and deep radio observations from the MeerKAT Absorption Line Survey, we have established a sample of ≈6000 spectroscopically identified galaxies in 11 distinct fields to constrain the neutral gas content at intermediate redshifts. The galaxies sample a broad range in stellar mass, from log M star / M ⊙ ≈ 8 to log M star / M ⊙ ≈ 11 , with a median of 〈 log M star / M ⊙ 〉 med ≈ 10 and a wide range in redshift from z ≈ 0.24 to z ≈ 0.63 with a median of 〈 z 〉 med = 0.44. While no individual galaxies show detectable H i emission, the emission line signal is detected in the stacked spectra of all subsamples at greater than 4 σ significance. The observed total H i 21 cm line flux translates to a H i mass, M H I ≈10 10 M ⊙ . We find a high H i -to-stellar-mass ratio of M H I / M star ≈ 6 for low-mass galaxies with 〈 log M star / M ⊙ 〉 ≈ 9.3 (>3.7 σ ). For galaxies with 〈 log M star / M ⊙ 〉 ≈ 10.6 , we find M H I / M star ≈ 0.3 (>4.7 σ ). In addition, the redshift evolution of H i mass, 〈 M H I 〉, in both low- and high-mass field galaxies, inferred from the stacked emission-line signal, aligns well with the expectation from the cosmic star formation history. This suggests that the overall decline in the cosmic star formation activity across the general galaxy population may be connected to a decreasing supply of neutral hydrogen. Finally, our analysis has revealed significant 21 cm signals at distances greater than 75 kpc from these intermediate-redshift galaxies, indicating a substantial reservoir of H i gas in their extended surroundings