Speaker : Donghui Quan (Zhejiang Laboratory)
Title: Modelling Interstellar Prebiotic Molecules: Hydroxylamine (NH2OH), Cyanamide (NH2CN), and Carbodiimide (HNCNH)
Abstract:
Interstellar molecules, commonly referred to as molecules found in the interstellar medium and circumstellar shells, have had around 300 molecules identified thus far (Müller et al., 2023). Over a third of these molecules are complex organic molecules, also known as COMs, revealing a broad range of complex chemistry found in various astronomical sources. Additionally, some interstellar molecules, particularly organic ones, act as precursors for biological molecules like amino acids and nucleosides, which astrophysicists find fascinating. These molecules are called prebiotic molecules and are primarily detected in star-forming areas, as well as quiescent clouds with nearby shocks.
Our research project utilizes computer-assisted modelling using chemical kinetics rate equations. We focus on hydroxylamine (NH2OH), cyanamide (NH2CN), and carbodiimide (HNCNH) isomers, which are known to act as precursors to amino acids or nucleosides. Our models provide an insight into the physical environments and associated chemical/physical processes of these species and related molecules. We identify primary formation and destruction reactions, optimal physical conditions for detecting these molecules, and related molecules. All these information may help with our understanding of astrochemistry in interstellar space, and enrich our knowledge of the complexity of the universe.
Speaker : Miguel Montarges (Observatoire de Paris)
Title: How do star end their lives ? Challenges, results, and perspectives at high angular resolution
Abstract: Cool evolved stars, namely asymptotic giant branch stars and red supergiant stars, experience an important mass loss (10-7 to 10-4 solar mass per year, while the solar wind represents ~10-14 solar mass per year). This stellar wind is enriched in heavy elements and contributes to the chemical evolution of the Galaxy. For massive stars, it can determine the final fate of the star as a neutron star or black hole. Yet, some of its mechanisms are still unknown: (1) the dust nucleation process is still unclear, (2) for low and intermediate mass stars the processes shaping planetary nebulae are not well constrained, (3) for massive stars we still do not know how the material is lifted from the photosphere. I will present recent high angular resolution results on cool evolved stars using adaptive optics, and optical and millimeter interferometry. I will conclude the presentation with an overview of a promising future thanks to a powerful new instrumentation.
Speaker : Olivier Berne (IRAP)
Title: Observations de la nébuleuse d’Orion avec le télescope spatial James Webb : implications pour la spectroscopie des galaxies de l’univers lointain et la formation planétaire
Abstract: Le télescope spatial James Webb a été lancé le 25 décembre 2021. Depuis l’été dernier, il observe avec succès l’univers local et lointain. Dans le cadre du programme Early Release Science intitulé « PDRs4All » (Berné, Habart, Peeters et al., 2022), notre équipe a pu disposer dès le mois de septembre d’observations de la Nébuleuse d’Orion réalisées avec le télescope Webb. Ces observations révèlent les effets du rayonnement UV lointain (FUV, c’est-à-dire des photons UV avec une énergie inférieure à la limite de Lyman de 13,6 eV) émis par les étoiles massives sur leur environnement, avec un niveau de détail inédit.
L’analyse préliminaire des données permet, d’une part, de caractériser le chauffage du milieu interstellaire par le rayonnement FUV des étoiles massives et le spectre infrarouge qui en découle, établissant ainsi une relation entre les signatures spectroscopiques et les conditions physiques. Cette relation pourra ensuite être utilisée pour interpréter les spectres des galaxies, même les plus lointaines, afin de mieux comprendre leurs propriétés.
D’autre part, les observations d’Orion ont permis de mettre en évidence un disque protoplanétaire irradié par les photons FUV. Cette irradiation crée un vent, entraînant une perte de masse du disque équivalente à environ 1% de la masse de la Terre par an. Cette perte de masse est suffisante pour empêcher la formation de planètes géantes autour d’étoiles de faible masse dans des amas contenant des étoiles massives, comme c’est le cas dans la nébuleuse d’Orion.
Le rayonnement FUV semble également avoir un effet sur la chimie du disque, produisant des hydrides tels que OH et CH+. Certaines signatures spectroscopiques présentes dans nos données, en cours d’identification, semblent correspondre à des espèces chimiques carbonées détéctées pour la première fois dans l’espace. Cette identification permettra, avec le soutien des expériences de laboratoire et la modélisation en physique moléculaire, de lever le voile sur des réseaux inexplorés de formation de molécules organiques.
O. Berné, E. Habart, E. Peeters, et al. (2022) Publications of the Astronomical Society of the Pacific 134 (1035)
Par : Melisse Bonfand (U. Virginia)
Titre: Physico-chemical evolution of high-mass star-forming regions
Abstract:
Stars with masses above 8 Msun are known to play a key role in setting up the physics and chemistry of the interstellar medium. Although these high-mass stars have been the prime targets of numerous observational and theoretical studies, the complex interplay between the physical and chemical processes involved in their formation is still a debated issue. The new capabilities of state-of-the art radio-interferometers, combining high-sensitivity and wide-bandwidth observations, together with the new sophisticated numerical chemical codes, have recently opened a new window on the study of high-mass star formation.
In my presentation I will focus on the hot and dense environment of young high-mass stars, known as hot core, which is an excellent laboratory to investigate the formation of complex organic molecules. I will present the first results obtained using a new gas-grain chemical kinetic code, coupled with a 2D radiative hydrodynamical model of star formation. The time-dependent predictions of the chemical models compared to the results derived from several ALMA observing programs that uncovered a large sample of star-forming sources, at different scales and different evolutionary stages, will allow us to determine up to which point the chemical composition of a source can help us to characterize its properties, nature, and evolutionary stage.
Titre: The polar regions of Jupiter
Par : Vincent Hue (LAM)
Abstract: The polar atmosphere of Jupiter is a complex region were (photo-)chemistry, dynamics and magnetospheric-coupling are intertwined. Several decades of ground-based observations and spacecraft measurements (Cassini, Juno) are progressively revealing how rich and complex these regions are. Species such as HCN, CO, H2O were brought during the Shoemaker-Levy 9 impact in 1994 and provide important dynamical tracers, as they have spread across Jupiter’s atmosphere over the last ~30 years. Hydrocarbons originate from methane-photolysis and are affected by auroral precipitations, leading to the formation of aerosols across the polar cap. Magnetosphere-ionosphere coupling generates powerful electrojets that drag the neutral stratosphere underneath. I will review our current understanding of these regions, based on observations from Cassini, Juno, ALMA, Gemini, and IRTF.
Titre: Streaming instabilities in modern protoplanetary disks
Par : Min-Kai Lin (ASIAA, Taiwan)
Abstract: The formation of km-sized planetesimals is a key step in providing the building blocks of planets. The streaming instability (SI) that arises from the mutual interaction between pebbles and gas is one of the leading mechanisms for planetesimal formation. Under appropriate conditions, the SI can drive the rapid growth of pebble enhancements to the point of gravitational collapse. However, the efficiency of the SI under more realistic conditions expected in protoplanetary disks has not been tested. To this end, I present extended models of the classic SI, including turbulence, stratification, magnetic fields, and non-isothermodynamics. I describe new challenges and pathways for planetesimal formation via the SI when these effects are considered.
Titre: Présentation de la résidence artistique de Benjamin Ducroq
Par : Benjamin Ducroq
Abstract:
Nous accueillons cet automne Benjamin Ducroq, metteur en scène, comédien et musicien en résidence artistique au LAB dans le cadre de la préparation d’un spectacle dont la création est prévue en novembre 2024.
Il nous présentera son projet puis nous aurons un temps d’échange où vous pourrez prendre contact avec lui si vous souhaitez participer à la résidence.
Origine(s)
Théâtre – musique – conférence immersive
Pour cette nouvelle création, la compagnie propose un voyage… un voyage à travers le temps, à travers l’infini sidéral, à travers le monde des idées, et ce pays fascinant et méconnu : les mathématiques. Elles sont fondamentales en sciences, et régissent notre monde. Elles sont le point de départ de notre travail, nous permettant d’ouvrir le champ d’étude aux lois de la physique et au cosmos.
Intitulé Origine(s), ce spectacle porté par le metteur en scène, comédien et musicien Benjamin Ducroq, prendra la forme d’un concert, d’une conférence et d’un dialogue avec les spectateurs sous un planétarium.
Pour réaliser ce spectacle qui verra le jour en novembre 2024, Benjamin Ducroq choisi de l’écrire avec les publics, et au plus près du terrain. Afin de s’inspirer, et de partager une réelle aventure artistique et scientifique, s’organiseront des résidences en laboratoire de recherche mais aussi en milieu scolaire.
Titre: Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift
Par : Yaherlyn Diaz
Abstract:
An interesting feature in AGN accreting at low rate is the weakness of the reflection features in their X-ray spectra, which can result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low luminosity AGN (LLAGN) would have a different reflector configuration compared with high luminosity AGN. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy combining data from XMM-Newton + NuSTAR+Swift. We use XMM-Newton + NuSTAR + Swift observations of a hard X-ray-flux limited sample of 17 LLAGN from BASS/DR2 with accretion rates λ_Edd<10^−3. We fit all spectra using a reflection model for torus and accretion disk reflectors. We found a tentative correlation between the torus column density and the accretion rate, LLAGN shows a lower column density compared with the high-luminosity objects. We also confirm the relation between Γ and λ_Edd, with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at λ_Edd ~10^−3, suggestive of a different accretion mechanism compared with higher accretion AGN.
Titre: The structure and history of the Milky Way disc, as told by its star clusters
Par : Tristan Cantat (MPIA)
Abstract:
The Gaia mission has had a huge impact on our ability to detect, classify, and characterise stellar aggregates in the Milky Way. It has greatly improved the census of star clusters of all ages, from the Solar neighbourhood to the edge of the Galaxy. Gaia has revealed the complex spatial structure of young associations, and shown that their overall distribution only weakly correlates with the expected spiral pattern of the Milky Way. At the other end of the timeline, we are now able to visualise the process of cluster disruption, and to map the spatial distribution of clusters up to several Gyr with unprecedented precision, unraveling the evolution of the Milky. Despite the recent advances, we still do not know what are the main parameters that allow some clusters to survive to old ages, or even if the Milky Way is still forming gravitationally bound clusters. The upcoming ground-based campaigns WEAVE and 4MOST as well as future space-based astrometric missions such as JASMINE and GaiaNIR hold the keys to better understanding the cluster population in the Milky Way.