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.
Title: How do stars get their mass? Understanding the origin of the IMF from the mass distribution of cores
Speaker: Dr. Thomas Nony (UNAM)
Abstract:
Title: Shaping Extrasolar Systems with Giant Planets
Speaker: Laetitia Rodet (Department of Astronomy, Cornell University )
Abstract:
In the last decades, exoplanet surveys have revealed the presence of giant planets (Jupiter-sized or larger) orbiting at least 5 % of Sun-like stars. This percentage will likely increase in the near future, in particular with the coming data releases of the Gaia mission. Due to their mass, giant planets have a significant impact on the dynamics of the entire planetary system. First insights on their architecture show larger eccentricities and inclinations than the smaller planets, and orbital periods ranging from hours (hot Jupiters) to years (cold Jupiters), and even thousands of years.
In this talk, I will present how giant planets shape the architecture of extrasolar systems, in particular the orbits of fellow giant planet companions, inner super Earths, moons and planetesimals. I will compare analytical expectations, N-body simulations, and actual observations, focusing especially on directly imaged-systems. Giant planets can directly perturb their environment through secular interactions, scattering or resonances. Moreover, cold Jupiters are sensitive to the close flybys of neighboring stars. The occasional kicks that those flybys induce can significantly change a giant planet orbit, which will then impact the rest of the planetary system. This phenomenon could be linked to the formation of hot Jupiters, the misalignment of inner super Earths or the asymmetries in debris disks.
Title: Disks around evolved binaries: do they form second-generation planets?
Speaker: Jaques Kluska (KU Leuven)
Abstract:
Title: Circumbinary envelope and wind mass transfer: from cool evolved stars to high-mass X-ray binaries
Speaker: Ileyk el Mellah (IPAG)
Abstract:
Stellar multiplicity has been recognized as a ubiquitous feature: stars seldom live an effectively single life. In the late stellar evolutionary stages, mass loss plays a major role while interaction with an orbiting companion can leave remarkable imprints in the circumbinary envelope and influence the final fate of the system. In binaries, whether the outflows are line-driven from a blue supergiant or dust-driven from a red giant, the flow morphology shares common features which shed light on the launching mechanism. High spatial and spectral resolution instruments have identified arcs and spirals around cool evolved stars which suggest the presence of underlying (sub-)stellar companions. On the other hand, in high-mass X-ray binaries, time-resolved spectroscopy over multiple orbits reveals how the clumpy wind is disrupted and accreted by the compact object.
In this talk, I will present simulations of mass transfer mediated by dust and line-driven winds in binaries. With the mesh-based radiative magneto-hydrodynamics code MPI-AMRVAC, we designed a versatile 3D setup suitable to capture the wind dynamics. In high mass X-ray binaries, we can follow the wind over several orders of magnitude as it is accreted onto the compact object. I will show how the compact object can also be used as an orbiting X-ray backlight whose shimmering betrays the structure of the foreground absorbing material. Around cool evolved stars, these simulations are extended up to several 10 orbital separations at an affordable computational cost, thanks to adaptive mesh refinement. For different dust chemical content, they can reproduce the morpho-kinematics properties we extracted from ALMA’s multi-channel molecular line emission maps. In both cases, I will describe how mass transfer redistributes angular momentum and can lead to orbital inspiral.
The seminar will be in French with the slides shown in English.
Title: La fin des systèmes planétaires/The fate of planetary systems
Speaker: Sylvie Vauclair (IRAP)
Abstract:
On étudie beaucoup la formation des systèmes planétaires, qu’en est-il de leur disparition ? L’étude des naines blanches apporte des informations importantes sur ce sujet. Après les épisodes d’expansion spectaculaire des étoiles dans les phases ultimes de leur existence, que reste-t-il de leurs systèmes planétaires ? Des disques de débris ont été découverts autour de nombreuses naines blanches. Des petits corps, de type astéroïde, encore présents dans le disque, sont épisodiquement détruits par effet de marée avant de tomber dans l’étoile. L’atmosphère est ainsi polluée en éléments lourds, dans des proportions montrant qu’il s’agit bien de restes d’anciens systèmes planétaires. Les simulations numériques du processus d’accrétion sur la naine blanche permettent d’évaluer le taux d’accrétion et d’estimer la masse des corps désintégrés. De récentes observations en rayon x confortent ce scénario.
Title: Détection d’exoplanètes froides dans toute la Voie Lactée avec les microlentilles gravitationnelles
Speaker: Etienne Bachelet
Abstract:
Depuis une vingtaine d’années, des dizaines d’exoplanètes « froides » ont été détectées à plusieurs kilo-parsecs de la Terre grâce aux microlentilles gravitationnelles. La grande majorité ont été observées en direction du bulbe galactique, ou la densité d’étoiles est la plus grande. Mais de nouveau grands relevés du ciel, tel que LSST, ouvrent la voie à la détection de microlentilles dans toute la Voie Lactée. En parallèle, la mission de la NASA Roman promet la détection de 1500 planètes à l’horizon 2035. Je présenterai le potentiel et les défis liés à ces nouvelles missions ainsi que les différentes synergies observationnelles.
Title: Unraveling stellar atmospheres and winds with Parker Solar Probe and Solar Orbiter
Speaker: Victor Reville (IRAP)
Abstract: