Titre : MHD non-idéale pour la formation d’étoile
Abstract :
Les effets de MHD non-idéale jouent un rôle primordial lors de la formation d’étoile et de disque. En découplant le champ magnétique du gaz, ils affaiblissent le freinage magnétique et les jets protostellaires, processus réduisant le moment cinétique du système. La force de ces effets dépend de l’ionisation du gaz et des grains, et donc de la chimie à l’oeuvre. Je montrerai l’impact de la distribution en taille de grains sur les effets de MHD non-idéale et sur le moment cinétique du gaz lors de l’effondrement protostellaire. Je présenterai également de nouvelles méthodes permettant de calculer rapidement la coagulation et l’ionization des grains.
Titre : Tides in multi-layer close-in planets
Abstract :
Many rocky exoplanets are detected on close-in orbits. For these planets, tides play an important role by changing their orbit and their rotation. In most studies on the orbital and rotational evolution of planets, simple tidal models have been used. But they are known to have flaws, in particular to correctly describe small rocky planets.
Title: How to detect extraterrestrial life: Laser-based Mass Spectrometry instruments on planetary science missions
Speaker: Dr. Niels F.W. Ligterink (SNSF Ambizione Fellow Space Research & Planetary Sciences division, Physics Institute, University of Bern)
Abstract: Life may exist or have existed on various planets and moons in our Solar System, such as Mars, Europa, or even Venus. Detecting extinct or extant life on these objects is challenging and, among other things, requires extraordinary instruments to do so. In this colloquium I will present the space instruments and methods that we develop at the University of Bern (Switzerland) to detect the chemical signatures of life. I will discuss the functioning of our Laser-based Mass Spectrometers, the types of biosignatures that we will detect with these instruments, and how we will employ them on space exploration missions.
Title: Modeling of protoplanetary disks physics and chemistry
Speaker: Dr. Maxime Ruaud (NASA postdoctoral program fellow, NASA Ames Research Center)
Abstract: The chemical composition of protoplanetary disks is inherited from their parent molecular clouds, but is expected to significantly evolve during the stages of planet formation. Disk chemistry not only dictates the inventory of material that gets assembled into planets, but also determines the abundances of species with bright, easily detectable emission lines. Gas line emission offers a window into the assembly process by allowing us to infer the physical conditions in the disk during planet formation epochs. Many disk properties, including fundamental ones such as gas mass and bulk elemental abundances are in fact inferred from these emission lines. For instance, recent studies on disk chemistry have inferred changes in the C/O and C/N ratios of disks, with implications for planetesimal formation and the composition of exoplanet atmospheres. These inferences are primarily based on ALMA detections of bright emission lines from trace species such as CO, C2H and CN and are linked . While these studies propose a direct link between the molecular emission observed in disks and planet formation processes, the use of these species to infer disks properties and chemical composition presupposes a good understanding of the chemistry taking place in disks, both in the gas phase and also in ice of dust grains. In this presentation I will show recent results obtained from a framework in which we self-consistently solve the time dependent gas-grain chemical composition of disks with a structure obtained from self-consistent thermo-chemical disk modeling including dust physics and detailed photochemistry. Based on these results, I will discuss the importance of using detailed models for interpreting past and future observations obtained from ground and space-based observatories such as ALMA, the IRAM or JWST.
Title: Unraveling the chemistry of planet-forming disks in the ALMA era
Speaker: Dr. Romane Le Gal (CNES post-doctoral researcher, IRAP)
Abstract: Over the past decades, questions on the origins and prevalence of life on planets have shifted from metaphysical questions to hot research topics in astrophysics. The latest generation of high-sensitivity telescopes has provided access to the cradles of star and planet formation at unprecedented spatial and spectral resolutions, making it possible to study the chemical evolution of interstellar matter from molecular clouds to forming planetary systems. A key question in this context is to assess how much of the pre-stellar molecular composition survives and becomes incorporated into planets. Or, conversely, how much nascent planets are affected by chemical reprocessing that occurs in their birth environments, i.e. in planet-forming disks around young stars. Indeed, these disks are exposed to energetic radiations and undergo strong dynamical phenomena such as planet formation, which may substantially alter their chemical inventory. In this talk I will present how my research combines observations and astrochemical modeling fed by theoretical and experimental studies to 1) better understand and characterize the chemistry of these disks, 2) start disentangling between chemical inheritance and chemical reprocessing in planet-forming disks, and 3) identify chemical signatures of planet formation.
Title: Exploration of the Jovian Outer Magnetosphere with Juno
Speaker: Vincent Hue (Research Scientist – Southwest Research Institute)
Abstract: Jupiter’s magnificent auroral lightshow is a direct manifestation of its strong magnetic field, which couples its magnetospheric plasma and ionosphere. In the ultraviolet spectral range, the Jovian auroras are highly structured, and reflect the numerous processes occurring throughout the magnetosphere. Since July 2016, NASA’s New Frontiers mission Juno performs in-situ and remote sensing measurements from within the Jovian magnetosphere. In this talk, we discuss the main auroral regions with a particular emphasis on the polar auroral regions, linked to the outermost region of Jupiter’s magnetosphere and possibly the solar wind. These are the most highly dynamic components of the Jovian auroras, often exhibiting flares evolving over short timescales. We present a new type of auroral feature recently discovered by the Ultraviolet Spectrograph on Juno (Juno-UVS), which consists in circular expanding UV-emission, and discuss their potential origin.
Title: Non-thermal cosmic ray desorption of ices mantles and complex organic molecules
Speaker: Emmanuel Dartois (Institut des Sciences Moléculaires d’Orsay (ISMO))
Abstract:
Title: Molecular diversity of early-stage high-mass protostars: evidence for a deeply embedded hot corino phase?
Speaker: Laure Bouscasse (IRAM)
Abstract:During star formation the molecular gas undergoes significant chemical evolution leading to a molecular richness at the emergence of hot cores. The chemical formation pathways even for simpler molecules are debated. Using a spectral survey between 159GHz and 374GHz with the APEX telescope, we investigated a sample of 6 massive clumps dominated by a single collapsing massive object down to 400au scales. In all 6 sources of the sample, on average 40 species were found. Through LTE modeling we could constrain the physical origin of these species within the envelope. While some objects exhibit a clear structure with a well-defined warm gas phase, some remain mostly cold with warm gas traced only by methanol and methyl cyanide. The molecular composition of the sample is remarkably similar: their molecular content is composed of the simplest molecules and the most complex ones in the cold component of envelope for all our objects. However, some differences in the molecular emission are found in the deuterated molecules, S-bearing molecules, and the COMs. Towards the warm component, the comparison of the relative molecular abundances shows an emerging warm gas phase with high molecular abundances for dimethyl ether, methyl formate, formamide, and the cyanides. Finally in our objects, we found similar relative abundances for O-bearing molecules relative to CH3OCH3 while cyanides exhibit remarkably higher abundances relative to CH3CN compared to hot corinos. Altogether we could characterize a phase preceeding the emergence of bright hot cores resembling in many aspects a deeply embedded hot corino phase in the emergence of high-mass protostars.
Title: What are the magnetic switchbacks observed by the mission Parker Solar Probe ?
Speaker: Naïs Fargette (Institut de Recherche en Astrophysique et Planetologie)
Abstract:
Near the Sun, the solar wind magnetic field is dominated by Alfvénic structures that undergo reversals of the radial magnetic field while keeping a constant strahl and constant magnetic field amplitude as well. They are called magnetic switchbacks and are interpreted as accelerated folds on the magnetic field in the solar wind. They were observed by numerous missions (Wind, Ulysses, Solar Orbiter) and were most striking in Parker Solar Probe data, below 0.3 AU. Their origin is still debated and scenarii include interchange reconnection at the Sun’s surface, propagation of alfvenic waves and a turbulence driven phenomenon. In this talk I will present some characteristics of the switchback structures, give an overview of the existing formation theories and describe the latest results on the topic.
Title: The bimodal A(Li) distribution of Milky Way’s thin disk dwarf stars and the Galactic scale events
Speaker: Santi Roca-Fàbrega (Universidad Complutense de Madrid)
Abstract: The lithium abundance, A(Li), in stellar atmospheres suffers from various enhancement and depletion processes during the star’s lifetime. While several studies have demonstrated that these processes are linked to the physics of stellar formation and evolution, the role that Galactic-scale events play in the galactic A(Li) evolution is not yet well understood. In this talk I will show that the observed A(Li) bi-modal distribution, in particular in the FGK-dwarf population of field stars, is not a statistical artefact but it is a consequence of a particular Milky Way star formation history profile combined with the stellar evolution’s 7Lii depletion mechanisms. I will show that A(Li) evolution can be used as an additional proxy for the star formation history of our Galaxy.
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Title: Cosmology (& astrophysics) with the Lyman alpha forest
Speaker: Ignasi Pérez-Ràfols (Sorbonne Université, Laboratoire de Physique Nucléaire et de Hautes Energies)
Abstract: The acceleration of the expansion rate of the Universe is yet to be explained. Several models, including LCDM, try to explain this acceleration. LCDM bases its explanation on a mysterious dark energy, adding up to ~75% of the total energy density of the Universe. Other models present modified theories of gravity to explain this effect. But which one is correct? The expansion history of the Universe is a great observable to discriminate between these models. I will talk about measurements of this expansion history at redshift greater than 2 using BAO with the Lyman alpha forest. I will talk about the most recent results from eBOSS, and also from the next generation of surveys that is currently starting: DESI and WEAVE. I will talk about how improving our knowledge of the Lyman alpha forest can help us not only with answering our cosmological questions, but also with our understanding on galaxy evolution.