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Juno radio occultations reveal the structure of Jupiter's cold northern polar vortex
No full textContext. Jupiter’s polar upper troposphere and stratosphere host a persistent cold vortex poleward of 65°N, but its detailed structure and dynamics have remained difficult to resolve.
Aims. The goal is to characterize the thermal structure and dynamics of the polar vortex using new and complementary remote sensing techniques.
Methods. We used a combination of high-resolution vertical profiles derived from Juno’s recent radio occultation measurements and mid-infrared imaging from the VLT/VISIR instrument. The former provided direct retrievals of temperature and density near and within the vortex, while VISIR imaging revealed spatial thermal contrasts across the region.
Results. Our analysis confirms the presence of a steep meridional temperature jump at 65°N, of about 7±1 K at 100 mbar, which is consistent with a strong vertical wind shear and a prograde polar stratospheric jet reaching up to 80 ms−1 at the 10 mbar level. We find the atmosphere to be thermally stable above 0.55 bar, reaching a Brunt-Väisälä frequency of 0.025 s−1 in the mid-stratosphere. Thermal contrasts observed in the infrared data align with the vertical structures inferred from radio occultations, which validates the presence and extent of the cold vortex.
Conclusions. These findings offer a quantitative analysis of the thermal structure and the dynamical behavior of Jupiter’s polar atmosphere and demonstrate the diagnostic power of combining radio occultation and thermal infrared techniques in planetary atmospheric studies
Deuteration of HC
No full textContext. Deuterated molecules are a useful diagnostic tool to probe the evolution and the kinematics in the earliest stages of star formation. Due to the low temperatures and high densities in the centre of pre-stellar cores, the deuterium fraction is enhanced by several orders of magnitude with respect to the cosmic D/H abundance ratio.
Aims. We study the distribution of the emission and the deuteration of the two carbon chains HC3N and CH3CCH throughout the prototypical pre-stellar core L1544.
Methods. We analyse emission maps of CH3CCH, CH2DCCH, CH3CCD, HC3N, HCC13CN, and DC3N, observed towards L1544 with the IRAM 30 m single-dish radio telescope. We use non-local thermodynamic equilibrium radiative transfer calculations, combined with chemical modelling of the molecular abundances, to constrain physical parameters of the observed species. Following this, we derive the corresponding column density and deuteration maps and analyse the chemical processes influencing the different molecular distributions.
Results. We find levels of deuteration of N(DC3N)/N(HC3N) = 0.04-0.07, N(CH2DCCH)/N(CH3CCH) = 0.09-0.15, and N(CH3CCD)/N(CH3CCH) = 0.07-0.09. The deuteration of HC3N appears homogeneous across the core, with widespread D-fraction values above 0.06, tracing intermediate-density gas in the outer layers of the core, at densities less than 105 cm−3. CH3CCD is most efficiently formed in the higher-density regions towards the core centre, while the deuteration fraction of CH2DCCH traces a local density enhancement in the north-east of the core, coinciding with the CH3OH emission peak.
Conclusions. The results suggest that gas-phase reactions dominate the formation and deuteration of both HC3N and CH3CCH in L1544, with spatial variations driven by physical structure, density and external radiation. The significantly higher deuteration fraction of CH2DCCH compared to CH3CCD and a tentative gradient with higher values in the north suggest that there are different deuteration mechanisms for the two functional groups, with varying efficiency across the core. Similarities between the CH2DCCH emission and CH2DOH might indicate an additional deuteration pathway of CH3CCH on the surfaces of dust grains, as observed for H2CO
The MURALES survey
No full textWe present the results of VLT/MUSE integral-field spectroscopy of the radio galaxy 3C 313 at z = 0.459, combined with HST and Chandra images. The high-resolution optical and X-ray images show the presence of two sources separated by 0.″63 (3.7 kpc). The narrow emission lines produced by highly ionized gas show a double-peaked profile, with a separation corresponding to ∼400 km s−1. No permitted broad lines are observed. We conclude that 3C 313 hosts a dual active galactic nucleus (AGN), with both nuclei being optically obscured type II. The low ionization [O I
Impact risk from the circumsolar dust ring on Venus’s orbit
No full textContext. A circumsolar dust ring on Venus’s orbit was discovered following observations by the Helios spacecraft and then confirmed thanks to observations by STEREO and the Parker Solar Probe. The impact risk it poses needs to be evaluated for any spacecraft crossing the ring.
Aims. This study aims to provide a basic model of the dust ring in terms of the distribution of particles (including size distribution) and the density of the ring and orbits and to deduce a first estimation of the impact risk to spacecraft crossing the ring. This impact risk is based on impact flux as well as the direction and speed of impacting particles.
Methods. We seek to describe the orbits of dust particles in the ring. We explored two ways to generate initial conditions of particles in the ring: one that involves many assumptions and another that is more reliable. We integrated the second set of orbits for 6000 years and studied their evolution. We then selected particles still inside the ring after this integration and used the orbits to compute the impact risk for a spacecraft chosen as an example, BepiColombo.
Results. We demonstrate that the dust ring will persist over the next 6000 years, extending radially and perpendicularly to the Venus orbital plane because of close encounters with Venus and because of non-gravitational forces. We show that particles tend to accumulate at Venus’s orbit, but along its orbit, the variations in density are negligible. We computed the number of particles we expect to find in the ring for radii between 2 μm and 2 cm (i.e. for masses between 10−2 kg and 10−14 kg). The size distribution of these particles is based on the interplanetary dust model IMEM2. Using the particles still inside the ring at the end of the integration, we computed the impact flux on BepiColombo due to the ring and show that it is of a similar level as the interplanetary dust background. Even though the impact flux is not negligible, it is low enough to be considered a very minor threat to spacecraft following an orbit similar to BepiColombo. Finally, we computed the velocity and direction of particles impacting BepiColombo and show that these results are not concerning.
Conclusions. We thus conclude that the dust ring is not a major threat to spacecraft following trajectories similar to BepiColombo. This model should be updated in the future with any new data on the ring, as such data are severely lacking at the moment
Positron-helium bound states in the scattering of polarized helium and orthopositronium
No full textThe formation of positron-helium bound states in a single rearrangement collision between spin-polarized beams of triplet helium and orthopositronium is studied. The probabilities of producing both doublet and quartet bound states are calculated using angular-momentum coupling and the construction of density matrices. The spin scattering matrix for the process and a table containing the probabilities for all possible final states are provided. The probabilities are expressed in terms of the real parts of complex scattering amplitudes labeled with total electron spin and the angle between the polarization vectors of the beams. Differences between cases in which the beam spins are aligned and those in which they are oppositely aligned are noted. The product of the polarization tensors of the beams is written as a function of the probabilities for certain angles. A description of how the real parts of the scattering amplitudes and annihilation rates for the bound states could be determined is given
Chemical enrichment in LINERs from MaNGA
No full textContext. Chemical abundance radial gradients provide key information on how the processes that affect chemical enrichment of the gas-phase interstellar medium (ISM) act at different galaxy scales. In the past decades, though there has been an increase in the number of galaxies studied with integral field spectroscopy, there is still not a clear picture on a subsequent characterization of the chemical abundance radial gradients in galaxies hosting active galactic nuclei (AGNs). This lack of studies is even more accentuated in the case of low-ionization nuclear emission-line regions (LINERs).
Aims. For the first time, we analyze the chemical abundance radial gradients in a sample of LINER-like galaxies, whose nuclear emission has been previously discussed (Paper I).
Methods. We used a sample of 97 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), whose nuclear regions show LINER-like emission. We used the open-source code HII-CHI-MISTR
Euclid preparation. LXXXIX. Accurate and precise data-driven angular power spectrum covariances
No full textWe develop techniques for generating accurate and precise internal covariances for measurements of clustering and weak-lensing angular power spectra. These methods have been designed to produce non-singular and unbiased covariances for Euclid's large anticipated data vector and will be critical for validation against observational systematic effects. We constructed jackknife segments that are equal in area to a high precision by adapting the binary space partition algorithm to work on arbitrarily shaped regions on the unit sphere. Jackknife estimates of the covariances are internally derived and require no assumptions about cosmology or galaxy population and bias. Our covariance estimation, called DICES (Debiased Internal Covariance Estimation with Shrinkage), first estimated a noisy covariance through conventional delete-1 jackknife resampling. This was followed by linear shrinkage of the empirical correlation matrix towards the Gaussian prediction, rather than linear shrinkage of the covariance matrix. Shrinkage ensures the covariance is non-singular and therefore invertible, which is critical for the estimation of likelihoods and validation. We then applied a delete-2 jackknife bias correction to the diagonal components of the jackknife covariance that removed the general tendency for jackknife error estimates to be biased high. We validated internally derived covariances, which used the jackknife resampling technique, on synthetic Euclid-like lognormal catalogues. We demonstrate that DICES produces accurate, non-singular covariance estimates, with the relative error improving by 33% for the covariance and 48% for the correlation structure in comparison to jackknife estimates. These estimates can be used for highly accurate regression and inference
Multiwavelength variability of quasar 3C 273 described by nonextensive statistical mechanics
No full textWe investigate whether the multiwavelength variability of quasar 3C 273 can be described in terms of nonextensive statistical mechanics. Using a dataset of 39 light curves spanning from radio to X-rays collected by the Integral Science Data Centre (ISDC) database, we apply the q-Gaussian formalism to determine the entropic index q for each spectral band. Our analysis reveals a nontrivial dependence of q on energy, with two prominent increases from radio to mm/submm and hard X-ray domains. The first linear trend is likely associated with synchrotron flares and thermal emission from hot dust, while the second may reflect inverse Compton processes in a turbulent jet environment. However, the second linear trend in the hard X-ray range lacks statistical robustness due to limited data or large measurement uncertainties. Interestingly, the q values show no clear correlation with the fractional variability amplitude , suggesting that q captures a different aspect of the source's dynamical behavior. These findings offer new insights into how different emission mechanisms and physical regions in AGNs may manifest distinct degrees of statistical complexity
Stability Analysis of a Stochastic Unemployment Model.
No full textThis paper investigates the effect of stochastic perturbations on the deterministic UEV framework, which characterizes the problem of unemployment in poor countries. It examines how the system behaves and stays stable under random fluctuations. We study the existence and uniqueness of the non-negative solution. Furthermore, we examine the asymptotic behavior of this solution by analyzing the stability of the system at equilibrium points under some conditions. Finally, some numerical simulations are performed to verify the theoretical analysis using Matlab
Prediction of the hot flow behaviour of a third generation advanced high-strength hot-formable steel
No full textMedium manganese steels provide numerous benefits in hot forming, including reduced blank reheating temperatures and critical quenching rates compared to conventional boron-added steels. Moreover, their enhanced strength and ductility make them a promising material for lightweight components in the mobility sector. In this study, the flow behaviour of a novel medium manganese steel is characterised and modelled to enable the simulation of hot forming processes. A forming and quenching dilatometer is utilised for isothermal tensile tests at different forming temperatures and strain rates. The specimens undergo heat treatment prior to forming, following a process route that includes annealing, cooling, and reheating to replicate the heat treatment at the steel producer and the hot forming at the parts manufacturer. An in-situ optical measurement system is used to determine the strains with digital image correlation. The experimental flow curves are modelled using various phenomenological hardening laws. Finally, the applicability of the hardening laws is verified by the simulation of a tensile test that was not used for modelling. The best prediction accuracy was achieved by the modified Norton-Hoff law, which provided a root mean square error of 14.4% during model calibration and a low mean absolute percentage error of 1.3% during validation