Calendar

Mar
30
mar
Maxime Ruaud – Modeling of protoplanetary disks physics and chemistry @ Zoom
Mar 30 @ 15 h 00 min – 16 h 00 min
Séminaire

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.

Avr
30
ven
Romane le Gal – Chemistry of planet-forming disks @ Zoom
Avr 30 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

Mai
4
mar
Vincent Hue – Exploration of the Jovian Outer Magnetosphere with Juno @ Zoom
Mai 4 @ 15 h 00 min – 16 h 00 min
Séminaire

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.

Juin
18
ven
Emmanuel Dartois – Non-thermal cosmic ray desorption of ices mantles and complex organic molecules @ Zoom
Juin 18 @ 11 h 00 min – 12 h 00 min
Séminaire

Title: Non-thermal cosmic ray desorption of ices mantles and complex organic molecules
Speaker: Emmanuel Dartois (Institut des Sciences Moléculaires d’Orsay (ISMO))

Abstract:

In the dense and cold zones of the interstellar medium, dust grains are covered with volatile solids, the interstellar ice mantles, which are relatively protected from ambient radiation fields external to dense clouds. However, cosmic radiation consisting of high-energy particles can penetrate deeply into these clouds and induces complex chemistry through its direct interaction (radiolysis), or indirect photolysis of dust grains (production of a secondary vacuum ultraviolet VUV radiation field by interaction with the gas, mainly molecular hydrogen).
 
The chemical evolution observed in high-density regions, from dense clouds to protoplanetary disks, and the release of species condensed on dust grains, is one key parameter to be taken into account in interpretations of both observations and models. Cosmic-ray-induced sputtering is one of the important desorption mechanisms at work in such astrophysical environments.
 
In this talk I will briefly describe the evolution, and the results based on laboratory experiments of interstellar ices analogues exposed to CRs simulated on particles accelerators, in the electronic regime of interaction, with a focus on the sputtering of ice mantles in an astrophysical context.
Oct
15
ven
Laure Bouscasse – Molecular diversity of early-stage high-mass protostars: evidence for a deeply embedded hot corino phase? @ B18N, Salle Univers
Oct 15 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

Oct
19
mar
Naïs Fargette – What are the magnetic switchbacks observed by the mission Parker Solar Probe ? @ B18N, Salle Univers
Oct 19 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

Oct
22
ven
Ignasi Pérez-Ràfols / Santi Roca-Fàbrega – Lyman alpha/disk dwarf stars @ B18N, Salle Univers
Oct 22 @ 11 h 30 min – 13 h 00 min
Séminaire

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.

——

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.

Nov
9
mar
Thomas Nony – How do stars get their mass? Understanding the origin of the IMF from the mass distribution of cores @ B18N, Salle Renaudot (216)
Nov 9 @ 11 h 00 min – 12 h 00 min
Séminaire

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:

The origin of stellar masses is one of the most central open issues in astrophysics. In this talk, I will introduce the ALMA-IMF Large Program, whose goal is to determine if and how the origin of the Initial Mass Function (IMF) depends on the cloud characteristics. Its first results, obtained from a large sample of cores without significant bias, suggest that mass distribution of cores (CMFs) in high-mass proto-clusters generally do not follow the canonical IMF.
I will also present our recent detailed studies of the W43-MM2&MM3 molecular complex. We propose that top-heavy CMFs are associated with spatially and temporally limited bursts of star formation. In addition, the identification of outflows in CO(2-1) enables us to assess that a very large fraction of the excess high-mass cores are protostellar. This confirms that the high-mass prestellar core phase, if it exists, is evanescent. Interestingly, protostellar outflows in W43 have also shown clear evidence of episodicity, bringing new elements toward the understanding of episodic accretion.
Nov
19
ven
Laetitia Rodet – Shaping Extrasolar Systems with Giant Planets @ Zoom
Nov 19 @ 14 h 00 min – 15 h 00 min
Séminaire

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.

Déc
3
ven
Jaques Kluska – Disks around evolved binaries: do they form second-generation planets? @ B18N, Salle Univers
Déc 3 @ 11 h 00 min – 12 h 00 min
Séminaire

Title: Disks around evolved binaries: do they form second-generation planets?
Speaker: Jaques Kluska (KU Leuven)

Abstract:

Most of the planets were formed around young stars. But can they also form around dying stars? 
The origin of the diversity and complexity of the detected exoplanetary systems stems from how they form in protoplanetary disks. These disks are intensively studied around young stars thanks to the high-angular resolution provided by recent instruments (VLT, ALMA). However, similar disks are also found around evolved stars, namely post-AGB binaries, raising the exciting but yet unanswered possibility of second-generation planet formation. Do planets form around evolved stars? While this question has only been tackled theoretically in the past, we have now the possibility to probe such second-generation planet formation by observations using high angular resolution instruments.
 
In this talk I will show the latest results of an extensive high angular resolution observing campaign of these disks using infrared interferometry at the VLTI (PIONIER, GRAVITY, MATISSE). I will show that these disks share many similarities with protoplanetary disks around young stars.
These disks are, therefore, a unique laboratory to test planet formation processes in a parameter space that is unmet around young stars (e.g., short disk lifetime, high stellar luminosity, lack of influence from the environment).
Whether or not planet formation is possible at the end of stellar evolution, studying it in a very different parameter space will provide an unprecedented test to current planet formation theories.