Astronomie

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    Identifying the energy release site in a solar microflare with a jet
    (Les Ulis : EDP Sciences, 2023) Battaglia, Andrea Francesco; Wang, Wen; Saqri, Jonas; Podladchikova, Tatiana; Veronig, Astrid M.; Collier, Hannah; Dickson, Ewan C. M.; Podladchikova, Olena; Monstein, Christian; Warmuth, Alexander; Schuller, Frédéric; Harra, Louise; Krucker, Säm
    Context. One of the main science questions of the Solar Orbiter and Parker Solar Probe missions deals with understanding how electrons in the lower solar corona are accelerated and how they subsequently access interplanetary space. Aims. We aim to investigate the electron acceleration and energy release sites as well as the manner in which accelerated electrons access the interplanetary space in the case of the SOL2021-02-18T18:05 event, a GOES A8 class microflare associated with a coronal jet. Methods. This study takes advantage of three different vantage points, Solar Orbiter, STEREO-A, and Earth, with observations drawn from eight different instruments, ranging from radio to X-ray. Multi-wavelength timing analysis combined with UV/EUV imagery and X-ray spectroscopy by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) is used to investigate the origin of the observed emission during different flare phases. Results. The event under investigation satisfies the classical picture of the onset time of the acceleration of electrons coinciding with the jet and the radio type III bursts. This microflare features prominent hard X-ray (HXR) nonthermal emission down to at least 10 keV and a spectrum that is much harder than usual for a microflare with γ = 2.9 ± 0.3. From Eartha's vantage point, the microflare is seen near the limb, revealing the coronal energy release site above the flare loop in EUV, which, from STIX spectroscopic analysis, turns out to be hot (i.e., at roughly the same temperature of the flare). Moreover, this region is moving toward higher altitudes over time (∼30akmas-1). During the flare, the same region spatially coincides with the origin of the coronal jet. Three-dimensional (3D) stereoscopic reconstructions of the propagating jet highlight that the ejected plasma moves along a curved trajectory. Conclusions. Within the framework of the interchange reconnection model, we conclude that the energy release site observed above-The-loop corresponds to the electron acceleration site, corroborating that interchange reconnection is a viable candidate for particle acceleration in the low corona on field lines open to interplanetary space.
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    The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries
    (Les Ulis : EDP Sciences, 2023) van der Wateren, E.; Bassa, C.G.; Cooper, S.; Grieβmeier, J.-M.; Stappers, B.W.; Hessels, J.W.T.; Kondratiev, V.I.; Michilli, D.; Tan, C.M.; Tiburzi, C.; Weltevrede, P.; Bak Nielsen, A.-S.; Carozzi, T.D.; Ciardi, B.; Cognard, I.; Dettmar, R.-J.; Karastergiou, A.; Kramer, M.; Künsemöller, J.; Osłowski, S.; Serylak, M.; Vocks, C.; Wucknitz, O.
    The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119-151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles, radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries have on average steeper radio spectra and longer spin periods (1.4×), as well as lower spin-down rates (3.1×) compared to the known pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra.
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    The Gaia-ESO survey: Mapping the shape and evolution of the radial abundance gradients with open clusters
    (Les Ulis : EDP Sciences, 2023) Magrini, L.; Viscasillas Vázquez, C.; Spina, L.; Randich, S.; Romano, D.; Franciosini, E.; Recio-Blanco, A.; Nordlander, T.; D'orazi, V.; Baratella, M.; Smiljanic, R.; Dantas, M.L.L.; Pasquini, L.; Spitoni, E.; Casali, G.; Van Der Swaelmen, M.; Bensby, T.; Stonkute, E.; Feltzing, S.; Sacco, G.G.; Bragaglia, A.; Pancino, E.; Heiter, U.; Biazzo, K.; Gilmore, G.; Bergemann, M.; Tautvaišienė, G.; Worley, C.; Hourihane, A.; Gonneau, A.; Morbidelli, L.
    Context. The spatial distribution of elemental abundances and their time evolution are among the major constraints to disentangling the scenarios of formation and evolution of the Galaxy. Aims. In this paper we used the sample of open clusters available in the final release of the Gaia-ESO survey to trace the Galactic radial abundance and abundance-to-iron ratio gradients, and their time evolution. Methods. We selected member stars in 62 open clusters, with ages from 0.1 to about 7 Gyr, located in the Galactic thin disc at galactocentric radii (RGC) from about 6 to 21 kpc. We analysed the shape of the resulting [Fe/H] gradient, the average gradients [El/H] and [El/Fe] combining elements belonging to four different nucleosynthesis channels, and their individual abundance and abundance ratio gradients. We also investigated the time evolution of the gradients dividing open clusters in three age bins. Results. The [Fe/H] gradient has a slope of −0.054 dex kpc−1. It can be better approximated with a two-slope shape, steeper for RGC ≤ 11.2 kpc and flatter in the outer regions. We saw different behaviours for elements belonging to different channels. For the time evolution of the gradient, we found that the youngest clusters (age < 1 Gyr) in the inner disc have lower metallicity than their older counterparts and that they outline a flatter gradient. We considered some possible explanations, including the effects of gas inflow and migration. We suggest that the most likely one may be related to a bias introduced by the standard spectroscopic analysis producing lower metallicities in the analysis of low-gravity stars. Conclusions. To delineate the shape of the ‘true’ gradient, we should most likely limit our analysis to stars with low surface gravity log g >  2.5 and microturbulent parameter ξ <  1.8 km s−1. Based on this reduced sample, we can conclude that the gradient has minimally evolved over the time-frame outlined by the open clusters, indicating a slow and stationary formation of the thin disc over the last 3 Gyr. We found a secondary role of cluster migration in shaping the gradient, with a more prominent role of migration for the oldest clusters.
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    A ∼15 kpc outflow cone piercing through the halo of the blue compact metal-poor galaxy SBS 0335-052E
    (Les Ulis : EDP Sciences, 2023) Herenz, E.C.; Inoue, J.; Salas, H.; Koenigs, B.; Moya-Sierralta, C.; Cannon, J.M.; Hayes, M.; Papaderos, P.; Östlin, G.; Bik, A.; Le Reste, A.; Kusakabe, H.; Monreal-Ibero, A.; Puschnig, J.
    Context. Outflows from low-mass star-forming galaxies are a fundamental ingredient for models of galaxy evolution and cosmology. Despite seemingly favourable conditions for outflow formation in compact starbursting galaxies, convincing observational evidence for kiloparsec-scale outflows in such systems is scarce. Aims. The onset of kiloparsec-scale ionised filaments in the halo of the metal-poor compact dwarf SBS 0335-052E was previously not linked to an outflow. In this paper we investigate whether these filaments provide evidence for an outflow. Methods. We obtained new VLT/MUSE WFM and deep NRAO/VLA B-configuration 21 cm data of the galaxy. The MUSE data provide morphology, kinematics, and emission line ratios of Hβ/Hα and [O ¯III]λ5007/Hα of the low surface-brightness filaments, while the VLA data deliver morphology and kinematics of the neutral gas in and around the system. Both datasets are used in concert for comparisons between the ionised and the neutral phase. Results. We report the prolongation of a lacy filamentary ionised structure up to a projected distance of 16 kpc at SBHα = 1.5 - 10-18 erg s cm-2 arcsec-2. The filaments exhibit unusual low Hα/Hβ 2.4 and low [Oa ¯III]/Hα ∼ 0.4 - 0.6 typical of diffuse ionised gas. They are spectrally narrow (∼20 km s-1) and exhibit no velocity sub-structure. The filaments extend outwards from the elongated Ha ¯I halo. On small scales, the NHI peak is offset from the main star-forming sites. The morphology and kinematics of Ha ¯I and Ha ¯II reveal how star-formation-driven feedback interacts differently with the ionised and the neutral phase. Conclusions. We reason that the filaments are a large-scale manifestation of star-formation- driven feedback, namely limb-brightened edges of a giant outflow cone that protrudes through the halo of this gas-rich system. A simple toy model of such a conical structure is found to be commensurable with the observations.
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    DREAM: I. Orbital architecture orrery
    (Les Ulis : EDP Sciences, 2023) Bourrier, V.; Attia, O.; Mallonn, M.; Marret, A.; Lendl, M.; Konig, P.-C.; Krenn, A.; Cretignier, M.; Allart, R.; Henry, G.; Bryant, E.; Leleu, A.; Nielsen, L.; Hebrard, G.; Hara, N.; Ehrenreich, D.; Seidel, J.; Dos Santos, L.; Lovis, C.; Bayliss, D.; Cegla, H.M.; Dumusque, X.; Boisse, I.; Boucher, A.; Bouchy, F.; Pepe, F.; Lavie, B.; Rey Cerda, J.; Ségransan, D.; Udry, S.; Vrignaud, T.
    The distribution of close-in exoplanets is shaped by a complex interplay between atmospheric and dynamical processes. The Desert-Rim Exoplanets Atmosphere and Migration (DREAM) program aims at disentangling those processes through the study of the hot Neptune desert, whose rim hosts planets that are undergoing, or survived, atmospheric evaporation and orbital migration. In this first paper, we use the Rossiter-McLaughlin revolutions (RMR) technique to investigate the orbital architecture of 14 close-in planets ranging from mini-Neptune to Jupiter-size and covering a broad range of orbital distances. While no signal is detected for the two smallest planets, we were able to constrain the sky-projected spin-orbit angle of six planets for the first time, to revise its value for six others, and, thanks to constraints on the stellar inclination, to derive the 3D orbital architecture in seven systems. These results reveal a striking three-quarters of polar orbits in our sample, all being systems with a single close-in planet but of various stellar and planetary types. High-eccentricity migration is favored to explain such orbits for several evaporating warm Neptunes, supporting the role of late migration in shaping the desert and populating its rim. Putting our measurements in the wider context of the close-in planet population will be useful to investigate the various processes shaping their architectures.