Calendar

Sep
13
mar
David Cornu – Winning the SKA Science Data Challenge 2 with a fast Deep Learning object detector @ B18N, Salle Univers
Sep 13 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : David Cornu (Obs de Paris)

Title: Winning the SKA Science Data Challenge 2 with a fast Deep Learning object detector

Abstract:
With its 1 TB simulated data cube of HI line emission, the SKA Science Data Challenge 2 (SDC2) is getting closer to the difficulty of real upcoming SKA observation analysis. Even if the type of task to perform in the SKA SDCs are rather classical (detection, classification, parameter extraction, etc.) modern datasets have become heavily demanding for classical approaches due to size and dimensionality. It is not a surprise then, that many astronomers started to focus their work on Machine Learning approaches that demonstrated their efficiency in similar applications. However, hyperspectral images from astronomical interferometers are in fact very different from images used to train state-of-the-art pattern recognition algorithms, especially in terms of noise level, contrast, object size, class imbalance, spectral dimensionality, etc. As a direct consequence, these methods do not perform as well as expected when directly applied to astronomical datasets. In this context, the MINERVA (MachINe lEarning for Radioastronomy at obserVatoire de PAris) project has assembled a team to participate in the SDC2 with the objective of developing innovative Machine Learning methods that better suit the needs of astronomical images.

In this presentation, I will describe the work we have made on implementing a modern YOLO (You Only Look Once) CNN object detector inside our custom framework CIANNA (Convolutional Interactive Artificial Neural Networks by/for Astrophysicists) and describe the modifications and tuning that allowed us to reach the first place of the SKA SDC2. I will start by discussing the strengths and weaknesses of this type of method in comparison to more widely adopted Region-Based CNN detectors (Faster R-CNN, Mask R-CNN, …). I will also review the motivation and the effect of the numerous changes we made on the method (data quantization, 3D convolution, layer architecture, detection layout to manage blending, objectness decomposition, IoU selection, additional parameter inference, …) in order to apply it to both SDC1 and SDC2, and identify what are the present limits as well as some tracks for further improvements. I will detail the computational efficiency of the method (with GPU acceleration) and discuss its scaling capabilities for upcoming challenges or datasets. Finally, we will comment on how this methodology could be used to analyze the actual data from SKA pathfinders or any other similar astronomical dataset and how it could be used to merge knowledge and information from multiple datasets at the same time.

 

Oct
4
mar
Martin Turbet – Le modèle « générique » de climats planétaires et panorama de ses applications @ B18N, Salle Univers
Oct 4 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Martin Turbet

Title: Le modèle « générique » de climats planétaires et panorama de ses applications

Abstract:   Le modèle générique de climats planétaires ou « Generic PCM » est un code communautaire, développé principalement et historiquement au LMD, et dont l’objectif est de simuler l’ensemble des processus physiques et chimiques opérant dans les atmosphères planétaires. Ses applications sont nombreuses : étude de la dynamique atmosphérique de Jupiter, Saturne et des géantes glacées, formation de brumes photochimiques sur Titan, évolution couplée de l’atmosphère et des glaces sur Pluton et Triton, paléoclimats de Mars, la Terre et Vénus, climats et observabilité des exoplanètes (des plus froides et petites aux plus grandes et chaudes), etc.
Après un bref aperçu du modèle et des briques qui le constituent, je vous présenterai un panorama de ses applications, avec une attention toute particulière sur les planètes et exoplanètes telluriques.

Oct
11
mar
Louis Amard – The evolution of young low-mass stars : focus on rotation and activity @ B18N, Salle Univers
Oct 11 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Louis Amard

Title: The evolution of young low-mass stars : focus on rotation and activity

Abstract: Between its formation stage as an active accreting seed and today, the Sun underwent large structural changes as well as variation in magnetic activity, rotation rate and its relation to the surrounding environment. I will go through the different processes that are responsible for these changes and present our latest results on the subject. We will go from the early interaction between the star and its proto-planetary disc bathing in UV radiations emitted from the massive neighbours, to the internal mixing happening in the inner layers of solar-like stars and probed by asteroseismology. Finally, I will try to review the possible applications of this work to other types of stars at different stages of the evolution in the context of the current or future surveys.

Oct
25
mar
Olivia Venot – On the importance of chemical data for warm exoplanet atmospheres @ B18N, Salle 306
Oct 25 @ 11 h 00 min – 12 h 00 min
Séminaire

Speaker : Olivia Venot (LISA)

Title: On the importance of chemical data for warm exoplanet atmospheres

Abstract: The very first data from JWST are finally arriving and show us the full potential of this telescope for the characterisation of exoplanet atmospheres. The interpretation of these data relies on atmospheric models, so it is of paramount importance that these models are reliable and robust. In this context I will show you the methodology applied to develop kinetic models adapted to the atmospheres of hot exoplanets, with physico-chemical data at high temperatures. I will also talk about the Hot Jupiter WASP-43b and the insights that JWST can give us into its atmosphere.

Jan
12
jeu
Laurent Chemin – Dynamics of the Milky Way and LMC as seen by Gaia @ B18N, Salle Chandon (306)
Jan 12 @ 11 h 00 min – 12 h 30 min
Séminaire

Speaker : Laurent Chemin (Universidad Andres Bello, Instituto de Astrofisica)

Title: Dynamics of the Milky Way and LMC as seen by Gaia

Abstract: 

Six months have passed since the Third Release of data from Gaia, the billion star surveyor of ESA. In this talk, I will present recent results obtained by the Gaia Collaboration with Gaia DR3 on the stellar dynamics of the Milky Way and the Large Magellanic Cloud. I will also describe how Gaia is changing our understanding of the evolution of the Local Group from the analysis of the orbits of dwarf galaxies around our Galaxy.

 

Jan
17
mar
Philippe Bonneton – Tidal bore dynamics in estuaries @ B18N, Salle Univers
Jan 17 @ 11 h 00 min – 12 h 30 min
Séminaire

Speaker : Philippe Bonneton (EPOC, CNRS/U. Bordeaux)

Title: Tidal bore dynamics in estuaries

Abstract:  A tidal bore is a sudden elevation of the water surface that travels upstream an estuary with the incoming flood tide. The formation and dynamics of this spectacular and fascinating phenomenon bring into play nonlinear wave interactions over a large range of spatiotemporal scales. A tidal bore is a small-scale estuarine process with scales of variation of order few seconds in time and dozen meters in space. This small-scale process, which generally occurs in the upper estuary, results from the nonlinear transformation of the tidal wave over long distance (several dozen of kilometers) and long period of time (several hours). The general bore phenomenon has been extensively studied in fluid mechanics and mathematics. On the other hand, the large-scale mechanisms which control tidal bore formation has so far received little attention. In this presentation we will analyze tidal bore formation from a unique long term database acquired during 4 campaigns in the two main French tidal-bore estuaries: the Seine and Gironde/Garonne estuaries. We will show that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We will also show that the undular bore structure can be explained by two different wave processes depending on the bore intensity.

Jan
24
mar
Camille Bergez-Casalou – Simultaneous accretion of giant planets or how giant planets fight for food @ B18N, Salle Univers
Jan 24 @ 10 h 30 min – 12 h 30 min
Séminaire

Speaker : Camille Bergez-Casalou (LESIA)

Title: Simultaneous accretion of giant planets or how giant planets fight for food

Abstract:  Among the thousands of exoplanetary systems observed nowadays, some of them host multiple giant planets, like in our Solar System. These giants are probably formed from the same protoplanetary disc. I’m going to present our recent paper where we investigated, with the help of 2D hydrodynamical simulations, how the gas present in the protoplanetary disc is distributed and accreted by two planetary cores. We start with 20 Me cores undergoing runaway gas accretion and follow the evolution of the planets mass ratio. We find that when the planets accrete from the same disc, they end up with very similar masses, independently on the disc viscosity or the delay in accretion between the planets. We finish by suggesting different formation scenarios in order to explain the observed exoplanets distribution.

Fév
7
mar
Damien Gratadour – Bridging Astronomy, HPC and AI in giant telescopes from the optical to radio frequencies @ B18N, Salle Univers
Fév 7 @ 11 h 00 min – 12 h 30 min
Séminaire

Speaker : Damien Gratadour

Title: Bridging Astronomy, HPC and AI in giant telescopes from the optical to radio frequencies
Abstract:  Frontier computing has become a key enabler for scientific discovery,  at the core of the next generation of extremely large multi-science hubs, such as the SKA Observatory or the European Extremely Large Telescope. I will present current efforts and the future roadmap we are contemplating, bridging astronomy with HPC and AI technologies to contribute to these major scientific infrastructures, in particular through the soon to be established ECLAT joint lab, a collaborative effort between CNRS, Inria and Atos. Beyond technical aspects related to increasing the scientific return of these facilities, I will also cover transverse topics such as energy efficiency and operational cost containment.

Fév
21
mar
Christine Ducourante – Gaia explore l’Univers profond: Galaxies, quasars et lentilles gravitationnelles @ B18N, Salle Univers
Fév 21 @ 11 h 00 min – 12 h 30 min
Séminaire

Speaker : Christine Ducourante (LAB)

Title: Gaia explore l’Univers profond: Galaxies, quasars et lentilles gravitationnelles

Abstract: 

Le satellite Gaia est en activité depuis 2013 et scanne sans relâche la voute céleste, mesurant tous les objets en deçà de ses limites de détections. Il mesure ainsi avec une incroyable résolution plusieurs millions de galaxies, certaines abritant des quasars et détecte même des lentilles gravitationnelles. Plusieurs groupes de travail du Data Processing and analysis Consortium (DPAC) Gaia se dédient à caractériser ces objets en les classant, mesurant leur redshift, ou leur morphologie. L’ensemble de ces travaux a été présenté pour la première fois dans la 3eme version du catalogue Gaia en Juin 2022. Par ailleurs, l’analyse du contenu du catalogue  Gaia permet d’identifier parmi 1.8 milliards de sources les « objets » rares et tant recherchés que sont les quasar multi-imagés par phénomène de lentille gravitationnelle. Je présenterai durant cet exposé l’ensemble des analyses et des propriétés de cet univers extragalactique de Gaia.
 
The Gaia satellite has been in operation since 2013 and tirelessly scans the celestial vault, measuring all objects below its detection limits. It thus measures with incredible resolution several million galaxies, some of which harbor quasars, and even detects gravitational lenses. Several working groups of the Gaia Data Processing and Analysis Consortium (DPAC) are dedicated to characterizing these objects by classifying them, measuring their redshift, or their morphology. These results were presented for the first time in the 3rd version of the Gaia catalog in June 2022. In addition, the analysis of the content of the Gaia catalog makes it possible to identify among 1.8 billion sources the rare and highly sought multi-imaged quasars by gravitational lensing. During this presentation, I will present all the analyzes and properties of this extragalactic universe of Gaia.
Fév
22
mer
Lars Bonne – Probing the assembly and dispersal of molecular clouds with the [CII] fine structure line @ B18N, Salle Univers
Fév 22 @ 10 h 00 min – 11 h 30 min
Séminaire

Speaker : Lars Bonne (USRA)

Title: Probing the assembly and dispersal of molecular clouds with the [CII] fine structure line
Abstract: 

I will present high spectral resolution observations of the ionized carbon fine structure line at 158 μm ([CII]) from the SOFIA FEEDBACK legacy survey. [CII] is a unique tracer of the CO-dark molecular gas and photodissociation regions (PDRs) at the surface of molecular clouds. The FEEDBACK survey maps the [CII] line in 11 Galactic high-mass star forming regions. First, I will present the [CII] observations of the DR21 ridge in Cygnus-X. There, [CII] unveils that the assembly of this massive star forming ridge is the result of a high-velocity (~20 km/s) colliding flow. This collision also curves the magnetic field around the ridge and thus sets the cloud geometry. Further investigating the molecular cloud dynamics with IRAM 30m observations shows that this rapid mass accumulation initiates gravitational collapse of the full molecular cloud. Then, I will present studies focusing on regions that experience the effect of stellar feedback from high-mass stars. In these regions, [CII] unveils high-velocity mass ejection from the clouds that is not seen in CO. Quantifying the mass ejection rate shows that stellar feedback can disperse these star forming clouds in a few Myr. These results point to a consistent scenario for molecular cloud evolution and star formation on relatively short timescales. Far-infrared fine structure lines are thus important tools to pin down the physical processes that drive the evolution of the interstellar medium (ISM).