Calendar

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. 
Déc
14
mar
Ileyk el Mellah – Circumbinary envelope and wind mass transfer: from cool evolved stars to high-mass X-ray binaries @ B18N, Salle Univers
Déc 14 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

Mar
16
mer
Sylvie Vauclair – The fate of planetary systems @ B18N, Salle Univers
Mar 16 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

 

Mar
18
ven
Etienne Bachelet – Détection d’exoplanètes froides dans toute la Voie Lactée avec les microlentilles gravitationnelles
Mar 18 @ 11 h 00 min – 12 h 00 min
Séminaire

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.

Avr
5
mar
Victor Reville – Unraveling stellar atmospheres and winds with Parker Solar Probe and Solar Orbiter @ B18N, Salle Univers
Avr 5 @ 11 h 00 min – 12 h 00 min
Séminaire

Title: Unraveling stellar atmospheres and winds with Parker Solar Probe and Solar Orbiter
Speaker: Victor Reville (IRAP)

Abstract:

Solar-like stars, and particularly the Sun, exhibit hot coronae that can reach temperatures of several million Kelvin, consequently driving expanding winds. Mechanisms for the heating and the acceleration of these winds are, however, still largely debated, with two main theories: dissipation through a turbulent cascade or direct heating through reconnection in the solar corona. Two novel heliospheric missions, Parker Solar Probe and Solar Orbiter, have been sent closer than ever to the Sun to settle the question.
 
In this talk, I will review and discuss 3D MHD models of the solar corona based on Alfvén wave turbulence and compare their results with the data of the two probes. I will also show the role of the reconnection in creating dynamic signatures in the solar wind. Understanding the dynamics of the corona is also crucial to anticipate solar-terrestrial relations and I will show recent efforts undertaken at IRAP for space weather modeling.
 
Finally, zooming out to a more stellar context, I will discuss the important constraints that need to be taken into account to transpose corona and wind models to other solar-like stars and their planetary systems.

 

Avr
12
mar
Michel Blanc – Horizon 2061 perspectives for the future exploration of Giant Planets systems @ B18N, Salle Univers
Avr 12 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Michel Blanc (astronome émérite à l’IRAP, directeur de l’Observatoire Midi-Pyrénées)

Title: Horizon 2061 perspectives for the future exploration of Giant Planets systems

Abstract : Giant Planet Systems offer four different examples of “small planetary systems” which are accessible both to in situ exploration and telescope observations inside our own planetary system. As described in the recently released report of the « Planetary Exploration, Horizon 2061 » foresight exercise ( https://horizon2061.cnrs.fr/publications/ ), exploration of these systems can address in depth six key science questions about planetary systems: exploring the diversity of their objects and the diversity of their architectures, understanding their formation scenarios and how they work, where to search for habitable worlds, and finally how to detect life. I will discuss how future space missions can address these questions in the decades to come. Finally, I will describe our current and future work on the coupling of giant planets atmospheres with their moons and magnetospheres, its current focus on the Jupiter System with Juno observations, and our plans to extend them to other giant planet systems and possibly to planet/moon/disk interactions.

Mai
31
mar
Anthony Boccaletti – Observations of exoplanetary systems at high angular resolution and high contrast: from ground to space @ B18N, Salle Univers
Mai 31 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Anthony Boccaletti (LESIA)

Title: Observations of exoplanetary systems at high angular resolution and high contrast: from ground to space

The two-last decade advances in exoplanetary science have been strongly connected to technological breakthroughs, especially in high contrast imaging. The past few years have witnessed a revolution in the field with the implementation of specialized ground-based instruments, like SPHERE at the VLT, equipped with extreme adaptive optics, stellar coronagraphs and dedicated post-processing algorithms. A new revolution is now coming with the James Webb Space Telescope being commissioned, expecting the first science programs to start in a few months.

I’ll briefly summarize the main results obtained with SPHERE in the first years of operations in what concern exoplanets and exoplanetary systems at large. I will focus on two systems which I studied in more details from a disk science point of view, AU Microscopii and AB Aurigae. To push even further the performances of SPHERE we are considering an upgrade of the AO system to explore the very close-in regions around bright stars and to access faint and red targets yet unattainable in star-forming regions, reinforcing the synergy with ALMA. I’ll discuss the main modifications of the instrument and the science cases associated with that upgrade. Finally, I’ll present the coronagraphic system of the Webb’s Mid IR instrument, MIRI, and the expected performance in terms of contrast and the complementarity with SPHERE.

Juin
28
mar
Bertrand Lefloch – Astrochimie des régions de formation d’étoile de type solaire – parcours d’un radioastronome @ B18N, Salle Renaudot
Juin 28 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Bertrand Lefloch (IPAG)

Title: Astrochimie des régions de formation d’étoile de type solaire – parcours d’un radioastronome

Les grands relevés systématiques de l’emission du gaz moléculaire dans le domaine (sub)millimétrique avec les intruments de l’IRAM et ALMA ont permis de grands progrès dans l’étude de l’ évolution de la matière interstellaire au cours des différentes phases de la formation des étoiles, depuis les condensations prestellaires jusqu’aux protoétoiles évoluées, et ainsi d’aborder la question de l’héritage chimique au cours de cette evolution. Cette question majeure de l’astrochimie a été au coeur des Grands Programmes ASAI et SOLIS que nous avons conduits avec IRAM 30m et NOEMA sur un échantillon de sources représentatives des différentes phases de la formation d’une étoile de type solaire. Malgré une statistique limitée sur le nombre de sources, les résultats obtenus éclairent l’évolution de la complexité moléculaire et la différentiation chimique dans les régions de formation d’étoiles, tout en améliorant notre compréhension des réseaux chimiques. Ces travaux ont également mis en évidence l’importance des phenomènes de perte de masse (jets) qui accompagnent la formation de la protoétoile, ainsi que leur impact sur les conditions physico-chimiques du milieu ambiant. Je terminerai en abordant quelques unes des questions posées après ASAI et SOLIS, sur l’évolution chimique des régions de formation d’étoiles, la différentiation chimique entre sources, l’influence des conditions environnementales. Celles-ci offrent de riches perspectives pour l’astrochimie et pour lesquelles une nouvelle approche dans l’analyse et la modélisation des données observationnelles est nécessaire.

Juil
5
mar
Thomas Lizée – From molecular gas to stars: Constraining the properties of resolved gas and dust disks of local spiral galaxies @ B18N, Salle Renaudot
Juil 5 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Thomas Lizee (Obs de Strasbourg)

Title: From molecular gas to stars: Constraining the properties of resolved gas and dust disks of local spiral galaxies

Milky Way observations have provided insight into the scaling relations of molecular clouds and their ability to form stars. However, these relations cannot be established in nearby galaxies due to the limited spatial resolution of available observations. Starting from the multiphase, multiscale analytical model of Vollmer et al. 2017, whose goal is to describe galaxies as clumpy turbulent accretion disks, we improved the model and applied it to a sample of 17 local spiral galaxies. We generated radial profiles of large-scale quantities (SFR, stars, total gas) as well as molecular line emissions of different species (CO, HCN, HCO+) and compared them to multi-wavelength observations. The model is then able to predict key properties of the ISM such as the Toomre parameter Q, the gas velocity dispersion, the characteristic timescales of molecular clouds (free fall, molecular gas formation and turbulent times) as well as the CO-to-H2 and HCN-to-H2(dense) conversion factors. We conclude our study by reproducing the radial profiles of a Virgo cluster galaxy, NGC 4654, affected by both ram pressure stripping and gravitational interactions to better understand how the ISM properties reacts to such perturbations.

Sep
6
mar
Jean-Marc Huré – Figures d’équilibres sphéroidales des fluides multicouches. @ B18N, Salle Univers
Sep 6 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Jean-Marc Huré (LAB)

Title: Figures d’équilibres sphéroidales des fluides multicouches.

J’exposerai les principaux éléments d’un formalisme vectoriel résolvant approximativement O(c) les configurations d’équilibre d’un fluide autogravitant hétérogène composé de L couches homogènes en rotation rigide et bordées par des sphéroides parfaits. Cette approche, basée sur un développement du potentiel gravitationnel sur le paramètre confocal c (plutôt que sur l’ellipticité e), permet des configurations très oblates, prolongeant ainsi les travaux classiques fin XIXe de l’école française. Ces solutions analytiques sont validées par les résultats numériques obtenus par la méthode SCF du champ auto-cohérent, et par l’établissement de l’équation du Viriel associée. Quelques perspectives ainsi qu’une application à la détermination de structures internes pour la planète Jupiter réalisant les principales observables seront présentées.

The slides will be in English, the seminar will be given in French.