CEA/DAp seminar organization

The Astrophysics Seminars of the DAp (Département d'Astrophysique) are held at the Orme des Merisiers campus of the CEA Saclay. The schedule is posted on this website. Unless otherwise posted, the seminar takes place at 10am on alternate Tuesdays in room Galilée (Building 713C).

Current seminar organization team: Frédéric GALLIANO, Pierre-Antoine FRUGIER, Matteo BUGLI, Carlos GOMEZ-GUIJARRO, Denise LANZIERI, Damien TURPIN.

Main official page for advertising the schedule: http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Seminaires/index.php?type=3








Past seminar and next ones (current date: December 9, 2022)


Tuesday

December 6

10:00
David ALONSO
(Oxford Department of Physics)

Modeling the birth and growth of the cosmic web


[click here for abstract]
In the last 10-20 years we have been able to observe vast swathes of the Universe at different wavelengths, allowing us to build high-sensitivity maps of different projected cosmic properties. The statistical correlation between these properties and the density inhomogeneities that underlie the cosmic large-scale structures can then be used to reconstruct the spatial distribution of fundamental cosmological and astrophysical quantities, as well as their evolution in time. In this talk, I will describe a number of methods used to carry out this kind of tomographic reconstruction, present measurements of fundamental properties (structure growth, gas pressure, star formation rate density) resulting from their application to existing data, and discuss the potential of near-future "Stage-IV" experiments to improve on and benefit from these methods, in their quest to improve our understanding of fundamental physics.

Local contact: Denise LANZIERI, organization: Denise LANZIERI

Tuesday

December 13

10:00
Recent hiree seminar / séminaire arrivant récent
Réza ANSARI
(DAp)

Cosmology with 21cm Intensity Mapping


[click here for abstract]
Intensity Mapping (IM) has been proposed about 15 years ago as an efficient technique to perform cosmological surveys. The 21cm hyperfine transition of neutral hydrogen can indeed be used to map the 3D distribution of matter in the universe, over a wide range of redshifts, from z=0 to z=3 or even z=6, bringing complementary information to the optical surveys. Since then, few dedicated instruments have been built (CHIME, Tianlai, BINGO) to explore the feasibility of the method; Other more ambitious instruments, such as HIRAX, CHORD or BINGO will be commissioned in the coming years. Intensity mapping surveys are also envisaged for SKA, in addition to the classical HI source surveys. After presenting the principle of 21 intensity mapping, I will briefly discuss its cosmological promises, as well as some of the associated instrumental and scientific challenges. I will then present some of the results of ongoing observations, focusing on Tianlai, and on PAON4. Tianlai is an international project that operates two pathfinder instruments, a cylinder array and a parabolic array, built in Xinjiang, in western China. PAON4 is a small test interferometer, located in Nançay, used to explore some of the technical aspects of compact radio arrays, operating in transit mode.

Local contact: Réza ANSARI, organization: Frédéric GALLIANO
Tuesday

January 10

10:00
Stéphane AUNE, Jean-Charles CUILLANDRE et Pierre ASTIER
(CEA, CEA/UPS et LPNHE)

Les 20 ans de MegaCam sur le Telescope Canada-France-Hawaii



Local contact: Pierre-Antoine FRUGIER, organization: Pierre-Antoine FRUGIER






Archives:

           





2022

Tuesday

February 1

10:00
Pascal TREMBLIN
(Maison de la Simulation)

Non-ideal self-gravity and cosmology: the importance of correlations in the dynamics of the large-scale structures of the Universe


[click here for abstract]
Inspired by the statistical mechanics of an ensemble of interacting particles (BBGKY hierarchy), we propose to account for small-scale inhomogeneities in self-gravitating astrophysical fluids by deriving a non-ideal Virial theorem and non-ideal Navier-Stokes equations using a decomposition of the gravitational force into a near- and far-field component. These equations involve the pair radial distribution function (similar to the two-point correlation function), similarly to the interaction energy and equation of state in liquids. Small-scale correlations lead to a non-ideal amplification of the gravitational interaction energy, whose omission leads to a missing mass problem, e.g., in galaxies and galaxy clusters. We also propose an extension of the Friedmann equations in the non-ideal regime. We estimate the non-ideal amplification factor of the gravitational interaction energy of the baryons to lie between 5 and 20, potentially explaining the observed value of the Hubble parameter. Within this framework, the acceleration of the expansion emerges naturally because of the increasing number of sub-structures induced by gravitational collapse, which increases their contribution to the total gravitational energy. A simple estimate predicts a non-ideal deceleration parameter qni~-1;this is potentially the first determination of the observed value based on an intuitively physical argument. We suggest that correlations and gravitational interactions could produce a transition to a viscous regime that can lead to flat rotation curves. This transition could also explain the dichotomy between (Keplerian) LSB elliptical galaxy and (non-Keplerian) spiral galaxy rotation profiles. Overall, our results demonstrate that non-ideal effects induced by inhomogeneities must be taken into account in order to properly determine the gravitational dynamics of galaxies and the larger scale universe.

Local contact: Frédéric GALLIANO, organization: Frédéric GALLIANO
Tuesday

February 8

10:00
Special seminar / séminaire exceptionnel
Ingo WALDMANN
(UCL)

Deep learning in exoplanet characterisation


[click here for abstract]
The use of machine and deep learning is prevalent in many fields of science and industry and is now becoming more widespread in extrasolar planet and solar system sciences. Deep learning holds many potential advantages when it comes to modelling highly non-linear data, as well as speed improvements when compared to traditional analysis and modelling techniques. However, their often ‘black box’ nature and unintuitive decision processes, are a key hurdle to their broader adoption. In this seminar, I will give an overview of deep learning approaches used in exoplanet characterisation and discuss our recent work on developing Explainable AI (XAI) approaches. XAI is a rapidly developing field in machine learning and aims to make ‘black box’ models interpretable. By understanding how different neural net architectures learn to interpret atmospheric spectra, we can derive more robust prediction uncertainties as well as map information content as function of wavelength. As data and model complexities are bound to increase dramatically with the advent of JWST and ELT measurements, robust and interpretable deep learning models will become valuable tools in our data analysis repertoire.

Local contact: Frédéric GALLIANO, organization: Frédéric GALLIANO
Tuesday

February 22

Vacations / Vacances
Vacances d'hiver
Tuesday

March 8

10:00
Cancelled / séminaire annulé
Leonardo TESTI
(DAp)

Protoplanetary disks and the dawn of planets


[click here for abstract]
In the classical picture of star and planet formation, disks are expected to form as a natural consequence of core collapse to form stars. Disks are then expected to mediate the extraction of excess angular momentum during the stellar accretion phase, and to be the locus of planet formation at later times. Reality is obviously much more complicated than this one line overview: disk properties “at birth” are a complex function of the star formation environment, the problem of transport in disks is far from being fully understood, as are the initial condition and timeline for planet formation. In this talk I will discuss some of these problems, mostly focusing on the successes and limitations of our understanding of the properties of individual disks and the global evolution of disk populations. I will discuss the current evidence for early planet formation in protoplanetary disks, and the open questions related to effect of the star formation environment across the Galaxy on disk properties and evolution, which likely also affect the planet formation process.

Local contact: Matteo BUGLI, organization: Matteo BUGLI
Tuesday

March 22

10:00
Benjamin WEHMEYER
(CSFK, Budapest)

Galactic Chemical Evolution of rapid neutron capture process elements using special, rare classes of supernovae, and of short lived radioisotopes


[click here for abstract]
The origin of the heaviest elements is still a matter of debate. For the rapid neutron capture process (r-process), multiple sites have been proposed, e.g., neutron star mergers and (sub-classes) of supernovae (e.g., magnetorotationally driven supernovae). R-process elements have been measured in a large fraction of metal-poor stars. Galactic archaeology studies show that the r-process abundances among these stars vary by over 2 orders of magnitude. On the other hand, abundances in stars with solar-like metallicity do not differ greatly. This leads to two major open questions: 1. What is the reason for such a huge abundance scatter of r-process elements in the early galaxy? 2. While the large scatter at low metallicities might point to a rare production site, why is there barely any scatter at solar metallicities? We use a high resolution three-dimensional Galactic chemical evolution model to simulate the abundances of r-process elements and short lived (<100 My) radioisotopes over the lifetime of the Galaxy, in order to better constrain the site of the r-process.

Local contact: Jérôme GUILET, organization: Matteo BUGLI
Tuesday

April 5

10:00
Barbara OLMI
(INAF, Italy)

Modeling Pulsar Wind Nebulae through their evolutionary phases


[click here for abstract]
Pulsar wind nebulae are fascinating systems, powered by the central rotating compact star, emanating a wind in the form of a relativistic, magnetized, and cold plasma that fills the nebula. They are visible as bright non-thermal sources in a very broad range of energies, from radio to gamma-rays. Observed morphologies vary with the evolutionary phase, with middle-aged and old systems strongly affected by the interaction with the ambient medium. Modeling of these sources requires some carefulness when going through the various phases, with a comprehensive description still lacking. Pulsar wind nebulae had been for a long time thought to contribute substantially to the positron excess in the CR spectrum at Earth -- potentially being the primary sources. In the last years, numerous evidence for efficient particle leakage by aged nebulae had been collected, showing up as quasi-monochromatic misaligned jets at X-rays in some cases, or in the form of extended TeV halos in others, reanimating somehow the interest in this class of objects. Here I will review our present knowledge of pulsar wind nebulae models through their different ages.

Local contact: Matteo BUGLI, organization: Matteo BUGLI
Tuesday

April 19

10:00
Sacha BRUN et Olivier LIMOUSIN
(DAp)

Solar Orbiter: the heliospheric explorer


[click here for abstract]
Solar Orbiter - ESA M1 Mission - has entered its scientific phase at the end of November 2021, after a cruise phase of more than 18 months (and 2.2 Billion km) and the commissioning of the 10 instruments on board. CEA/IRFU played a key role in this mission, by providing the focal plane detector array of the X-ray telescope, STIX, based on in-house Caliste technology. In the meantime, solar physicists have been busy preparing the pipelines needed to handle the data sent by the instrument, and developing high performance numerical simulations of the Sun. In this 2-voice seminar, we will relate the first 26 months of activities of the mission, covering both STIX calibration, its first light, the first solar flare detected, as well as the development of associated numerical simulations of the Sun and optimal scientific processing of instrumental data sent as the spacecraft gets closer and closer to the Sun (last perihelion was on 26 March 2022 at 0.32 AU), while in the meantime our star is increasing in intensity and in activity, with solar magnetic cycle 25 now well on its way.

Local contact: Pierre-Antoine FRUGIER, organization: Pierre-Antoine FRUGIER
Tuesday

May 3

Vacations / Vacances
Vacances de printemps
Tuesday

May 10

10:00
Group seminar open to everybody / séminaire de groupe ouvert à tous
Lev TITARCHUK
(University of Ferrara, Italy)

Comptonization Problem and Its solution in Application to the Spectra of the Neutron Star and Black Hole Sources


[click here for abstract]
In 2017 the work on the Comptonization (Sunyaev-Titarchuk) seen in the X-ray spectra of astrophysical sources was a candidate for the Nobel Prize in Physics. In this talk I provide all the details of the exciting prehistory of this topic and precise details of this discovery. The solution of this problem and its subsequent development and application to the spectra of accreting neutron star (NS) and black hole (BH) binaries reveals a lot of information on these objects. In particular, now we can unambiguously distinguish between a NS and a BH (Galactic or extragalactic) using correlations of their spectral indices vs mass accretion rate (or QPO frequency). I further demonstrate how we can determine a BH mass using this correlation.

Local contact: Philippe LAURENT, organization: Frédéric GALLIANO
Tuesday

May 17

10:00
Recent hiree seminar / séminaire arrivant récent
Benjamin MAGNELLI
(DAp)

A decade of the main-sequence of star-forming galaxies: New insights and perspectives on massive galaxy formation


[click here for abstract]
The observed tight correlation between the star formation rate (SFR) and the stellar mass of star-forming galaxies (SFGs) is now well constrained over the last 10 Gyr of look-back time. This so-called main sequence (MS), whose normalization declines from z~3 to 0, is commonly interpreted as evidence that SFGs are evolving primarily through a steady and long star-forming mode, likely sustained by the cold gas accretion along the cosmic web. Over the last decade, a plethora of studies have investigated within this framework the physical properties of SFGs along and across the MS, establishing key scaling relations between, e.g., the stellar mass, gas content, and/or morphology of SFGs in the SFR-stellar mass plane. In this talk I will review past and recent observational evidences of this new MS paradigm and how it has shaped our understanding of the evolution of massive galaxies. Then, I will present the limitations of this simple paradigm, and in particular how it fails to explain the more diverse than anticipated population of MS galaxies (e.g., starburst hidden within the MS), the importance of secondary parameters (e.g., environment) and the transition of SFGs to quiescence. I will conclude by presenting future observational opportunities that can be used to investigate this hidden complexity within the main sequence and to further unveil the physics involved in the evolution of massive galaxies over cosmic time.

Local contact: Benjamin MAGNELLI, organization: Carlos GOMEZ GUIJARRO
Tuesday

May 31

10:00
Cancelled / séminaire annulé
Elisa COSTANTINI
(SRON, Netherlands)

[TBA]



Local contact: Anne DECOURCHELLE, organization: Frédéric GALLIANO
Tuesday

June 14

10:00
Diego GÖTZ et Aline MEURIS
(DAp)

The MXT telescope on board SVOM: a new tool for time-domain and multi-messenger astrophysics


[click here for abstract]
The Sino-French SVOM (Space based astronomical Variable Object Monitor) mission is ready for launch in 2023. This mission is dedicated to the study of Gamma-Ray Bursts and other transient and variable sources of the high-energy sky. On board SVOM there will be four instruments, ECLAIRs and GRM, with large field of views, operating in the hard X- and gamma-ray domain, and two narrow field instruments: the Visible Telescope (VT) and the Microchannel X-ray Telescope (MXT). The MXT is a novel kind of compact and light instrument based of the « Lobster Eye » optical concept, coupled to a low noise state-of-the art X-ray camera, the latter being designed and manufactured at CEA Irfu. For a total mass of 42 kg and a total power of 60 W, this instrument is composed of an optics system, a telescope tube in carbon fiber, a radiator, a camera and a data processing unit. The 9 kg camera consists of a focal plane assembly with a detector assembly and thermoelectrical coolers, a front-end electronics assembly, a calibration wheel assembly and a support structure assembly. We will first review the SVOM scientific objectifs and how MXT will contribute to reach them. Then we will present the MXT design in more detail, focussing on the CEA contribution, and finally we will present the results of the calibration campaign performed in 2021 before the delivery of the telescope to Cnes.

Local contact: Pierre-Antoine FRUGIER, organization: Pierre-Antoine FRUGIER
Tuesday

June 21

10:00
Recent hiree seminar / séminaire arrivant récent
Sandrine CODIS
(DAp)

Modeling the birth and growth of the cosmic web


[click here for abstract]
Starting from the largest scales, I will first describe how the cosmic web is woven across cosmic time into a gigantic bubble-like tapestry made of nodes, filaments, walls and voids. A particular emphasize will be put on the geometry and connectivity of this cosmic foam. Recent theoretical works aiming to precisely model the Universe on those mildly non-linear scales will be presented. In particular, I will identify a regime where large-deviation theory can be successfully implemented to predict the so-called count-in-cells statistics and describe promising cosmological applications for future galaxy surveys. The second part of the talk will focus on the birth and evolution of haloes and galaxies within these large cosmic highways. The highly anisotropic galactic environment set by the cosmic web will be shown to play a significant role in shaping them, an effect inducing large-scale galaxy alignments that are difficult to model but represent an important contamination for weak lensing experiments.

Local contact: Sandrine CODIS, organization: Carlos GOMEZ GUIJARRO
Tuesday

July 12

Vacations / Vacances
Vacances d'été
Tuesday

September 6

10:00
Group seminar open to everybody / séminaire de groupe ouvert à tous
Nicolas SCEPI
(CU Boulder)

Formation, Evolution and Radiation of Magnetized Accretion Disks around Black Holes


[click here for abstract]
The impact of magnetic fields on the evolution and on the observational signatures of accretion disks is very uncertain. This uncertainty is mainly due to a lack of observational constraints on the magnetic field geometry or strength in accretion disks. However, even from a theoretical point of view our understanding of magnetized disks remains relatively poor. Indeed, analytic models of magnetized disks often need inputs from numerical simulations and numerical simulations of magnetized disks are difficult to perform and/or interpret. Because of this lack of magnetized disk models, standard disk models often reduce the magnetic field to a source of turbulence; turbulence through which the accretion can happen. While this simplification may hold for weakly magnetized disks, a large number of numerical simulations have shown that the role of a strong magnetic field goes far beyond producing turbulence. In particular, a strong magnetic field can produce powerful outflows, induce accretion through vertically elevated layers or non-axisymmetric structures, modify the time scales of accretion, enhance dissipation of gravitational energy in the disk and accelerate particles to very high energies. All of these effects dramatically affect the evolution and observational signature of accretion disks and open up new and exciting avenues to resolve outstanding problems of the standard accretion disk theory. In this talk, I will present an overview of my recent results on how strongly magnetized disks form, evolve and radiate. I will show in particular how strongly magnetized disks could explain events of very strong variability in AGNs, the flaring behavior of the Galactic center and the hardest emission in X-ray binaries.

Local contact: Jérôme RODRIGUEZ, organization: Matteo BUGLI
Tuesday

September 13

10:00
Special seminar / séminaire exceptionnel
Elisabeth KOHLER
(CNRS)

Agir pour l’égalité professionnelle entre les femmes et les hommes


[click here for abstract]
De la scolarité aux postes à responsabilité de nombreux stéréotypes persistent qui souvent entravent la carrière scientifique des femmes. L’objectif de ce séminaire est d’identifier ces biais et de présenter des exemples de mesures concrètes pour y remédier et mettre en oeuvre des politiques d’égalité professionnelle entre les femmes et les hommes. Différents sujets seront abordés, tels que les critères d’évaluation, les actions de communication, le congé maternité et la parentalité, la lutte et la prévention contre les violences sexistes et sexuelles.

Local contact: Anaëlle MAURY, organization: Frédéric GALLIANO
Tuesday

September 27

10:00
[TBA]
Tuesday

October 4

10:00
Special event / Evénement exceptionnel
Local Meeting
(DAp)

ARIEL



Local contact: [-], organization: [-]
Tuesday

October 11

10:00
Special radio seminar / séminaire spécial radio
Françoise COMBES
(LERMA)

Overview of Cosmology with SKA, the Square Kilometer Array


[click here for abstract]
SKA is a new technology radio-telescope array, about two orders of magnitude more sensitive and rapid in sky surveys than present instruments. It will be able to detect and measure the redshifts of billions of galaxies at the redshifts up to z=2, to probe through baryonic acoustic oscillations the nature of dark energy; it will probe the cosmic dawn of the universe, just afer recombination, and during the epoch of reionisation (z=6-15); it will be the unique instrument to map the atomic gas in high redshift galaxies, and determine the amount and distribution of dark matter in the early universe. With SKA-VLBI, it will unveil the accretion and feedback processes near super-massive black holes, and results from precursors will be shown. We will discuss these exciting perspectives, which will concretize at the end of the decade.

Local contact: Marc-Antoine MIVILLE-DESCHÊNES, organization: Marc-Antoine MIVILLE-DESCHÊNES
Tuesday

October 18

10:00
Special event / Evénement exceptionnel
Local Meeting
(DAp)

The future of large-format IR detectors



Local contact: Marc SAUVAGE, organization: Marc SAUVAGE
Tuesday

October 25

Vacations / Vacances
Vacances de la Toussaint
Tuesday

November 8

10:00
Philippe Laurent, Aymeric Sauvageon, Jérôme Rodriguez
(DAp)

INTEGRAL : 20 ans dans l'espace pour une aventure de plus de 35 ans


[click here for abstract]
Le laboratoire INTErnational d'Astrophysique des Rayons Gamma (INTEGRAL) a été lancé le 17 octobre 2002 de Baikonour (Kasakstan). Depuis lors il est resté sur son orbite elliptique de haute excentricité (environ 3 jours) effectuant 2568 révolutions (au 8 novembre 2022) autour de la Terre pour environ 530 Ms (méga secondes) d'observations scientifiques. Cette mission de taille moyenne transporte deux instruments principaux opérant dans le domaine spectral des rayons X durs et des rayons gamma mous (20keV-10 MeV), dont l'optique est basée sur le concept de masques codés : l'un est dédié à l'analyse spectrale fine avec des capacités d'imagerie modérées (SPI), l'autre est dédié à l'imagerie fine (ou presque) avec des capacités spectrales modérées (IBIS). Ces 20 ans dans l'espace sont le résultat d'au moins 15 ans de développement du projet avant qu'INTEGRAL puisse dévoiler le mystère du ciel à haute énergie. Le Dap a été profondément impliqué dans cette aventure de longue haleine, depuis le tout début du développement du concept de la mission (grande implication dans les deux instruments, ISGRI et SPI, participation au centre de données, développement de l'analyse s/w, suivi de la caméra) jusqu'à l'analyse actuelle des données en temps réel et des archives, avec un grand nombre d'articles publiés dans tous les domaines permis par les capacités instrumentales et même au-delà. Nous allons, dans ce séminaire, résumer ces plus de 35 ans en présentant divers aspects du projet/de la mission, en nous concentrant particulièrement sur ceux où l'implication du Dap a été cruciale. Nous commencerons par une vue d'ensemble de l'histoire de la mission, des principales caractéristiques instrumentales et des objectifs scientifiques au lancement, puis nous nous concentrerons sur la caméra ISGRI, la couche de détection 20-250 keV du télescope IBIS, qui est suivie au Dap tous les jours. ISGRI a été développée à l'IRFU et a obtenu la plupart des résultats d'INTEGRAL. Nous conclurons par un aperçu rapide et évidemment biaisé de quelques résultats scientifiques obtenus au cours de ces 20 années. Le séminaire sera présenté en Français avec des diapositives en Anglais par Philippe Laurent, Aymeric Sauvageon et Jérôme Rodriguez, bien humblement au nom d'un grand nombre de collègues anciens et actuels. ------------------------------------ ENGLISH VERSION INTEGRAL : 20 years in space and for a 35+ years adventure The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) has been launch on October 17th, 2002 from Baikonour (Kasakstan). Since then it has remained on its high-eccentricity elliptical orbit (about 3 days) performing 2568 revolutions (as of Nov. 8th, 2022) around the Earth for around 530 megaseconds of scientific observations. This medium sized mission caries two main instruments operating in the spectral domain of hard X-rays/Soft Gamma-rays (20keV-10 MeV), whose optics is based on the concept of coded masks: one is dedicated to fine spectral analysis with moderate imaging capabilities (SPI) the other is dedicated to fine(-ish) imaging with moderate spectral capabilities (IBIS). These 20 years in space are the results of at least 15 years of project development before INTEGRAL could unveil the mystery of the high-energy sky. The DAp has been deeply involved in this long-term adventure from the very beginning of the mission concept development (large involvement in both instruments, ISGRI and SPI, participation to the data centre, development of the s/w analysis, monitoring of the camera) to the current analysis of real time and archival data, with a large number of published papers in all fields allowed by the instrumental capabilities and even beyond. We will, in this seminary, summarised these 35 years+ by presenting various aspects of the project/mission, focusing especially on those where the involvement of the Dap has been crucial. This will start with an overall overview of the mission history, the main instrumental characteristics and scientific goals at launch, followed by a focus on the ISGRI camera, the 20-250 keV detector layer of the IBIS telescope, which is followed-up at DAp every days. ISGRI has been developed at IRFU and obtained most of the INTEGRAL results. We will conclude with a quick and obviously biased overview of some scientific results obtained over these 20 years. The talks will be given by Philippe Laurent, Aymeric Sauvageon, and Jérôme Rodriguez humbly on behalf of many, many former and current colleagues and presented in French with slides in English. Local contact & organizer: Pierre-Antoine FRUGIER

Local contact: Pierre-Antoine FRUGIER, organization: Pierre-Antoine FRUGIER
Tuesday

November 15

10:00
Large project seminar / séminaire grand projet
Anaëlle MAURY
(LFEMI)

Magnetic fields from star-forming cores to protostellar disks: a review of major contributions from the MagneticYSOs project


[click here for abstract]
Wherever we have the means of observing them, magnetic fields are detected across the full spectrum of astrophysical environments, from our own Earth, to stars, and cosmological structures. Magnetic fields are also present at all scales and evolutionary stages of star-forming structures. They have long been suspected to play a key role in shaping the typical outcome of the star formation process, such as stellar mass, spin, and multiplicity, or even the fate of stars towards their ultimate stages. In this talk, I will provide a global outlook on the progresses made in the recent years to characterize the role of magnetic fields during the embedded phases of the star formation process. Thanks to the development of observational capabilities and the parallel progress in numerical models capturing most of the important physics at work during star formation, the MagneticYSOs team successfully confronted detailed predictions of magnetized models to observational properties of the youngest protostars. I will present the physical processes and observational methods allowing to trace the magnetic field in embedded protostars, and review the main steps, success and limitations in comparing real observations to synthetic observations from the non-ideal MHD models. I will show how our work has shed light on the physical conditions required to ensure an efficient magnetic field coupling, and present unexpected results regarding the two main agents responsible for the coupling in star-forming cores: dust grains and ionized gas. Following this Ariane thread, I will argue our observational and theoretical findings support a novel scenario where the angular momentum problem for star formation may be actually “solved” not by the formation of large protoplanetary disks but by the combination of 1) lack of organized rotation motions at large envelope radii, 2) the inefficient angular momentum transport due to magnetic braking in the inner envelope (and angular momentum removed through rotating outflows generated by the presence of the magnetic field), and 3) a local origin of the angular momentum incorporated in the star–disk system. Reference review: https://ui.adsabs.harvard.edu/abs/2022FrASS...9.9223M/abstract

Local contact: Anaëlle MAURY, organization: Frédéric GALLIANO
Tuesday

November 22

10:00
Recent hiree seminar / séminaire arrivant récent
Antonio GARCIA MUÑOZ
(DAp)

Exoplanet atmospheres: An anticipated revolution


[click here for abstract]
The launch of the JWST less than a year ago is expected to set a turning point in exoplanet science, which is progressively transitioning from detection and population statistics to in-detail characterization of the exoplanets’ atmospheres. In this talk, I will present an admittedly biased perspective of what this may represent for our understanding of exoplanets, and how ongoing theoretical work and future telescopes may build upon JWST’s legacy.

Local contact: Antonio GARCIA MUÑOZ, organization: Frédéric GALLIANO
Tuesday

November 29

10:00
Elisa COSTANTINI
(SRON, Netherlands)

The cold and dusty medium in our Galaxy as seen in the X-rays


[click here for abstract]
X-rays have unique advantages in studying absorption and scattering from interstellar dust. For example, sharp and deep absorption features of Mg, Si, O and Fe, which are the building blocks of silicates, fall in the X-ray band. Present X-ray observatories already delivered to us interesting results, challenging the common paradigm on interstellar dust chemical and physical characteristics. Future instruments will open up an unexplored window, revealing the most dense environments of our Galaxy. In this talk I will illustrate the state-of-art of our understanding of dust as seen in the X-rays, and future prospects, using for example, the upcoming XRISM satellite.

Local contact: Anne DECOURCHELLE, organization: Frédéric GALLIANO
Tuesday

December 6

10:00
David ALONSO
(Oxford Department of Physics)

Modeling the birth and growth of the cosmic web


[click here for abstract]
In the last 10-20 years we have been able to observe vast swathes of the Universe at different wavelengths, allowing us to build high-sensitivity maps of different projected cosmic properties. The statistical correlation between these properties and the density inhomogeneities that underlie the cosmic large-scale structures can then be used to reconstruct the spatial distribution of fundamental cosmological and astrophysical quantities, as well as their evolution in time. In this talk, I will describe a number of methods used to carry out this kind of tomographic reconstruction, present measurements of fundamental properties (structure growth, gas pressure, star formation rate density) resulting from their application to existing data, and discuss the potential of near-future "Stage-IV" experiments to improve on and benefit from these methods, in their quest to improve our understanding of fundamental physics.

Local contact: Denise LANZIERI, organization: Denise LANZIERI
Tuesday

December 13

10:00
Recent hiree seminar / séminaire arrivant récent
Réza ANSARI
(DAp)

Cosmology with 21cm Intensity Mapping


[click here for abstract]
Intensity Mapping (IM) has been proposed about 15 years ago as an efficient technique to perform cosmological surveys. The 21cm hyperfine transition of neutral hydrogen can indeed be used to map the 3D distribution of matter in the universe, over a wide range of redshifts, from z=0 to z=3 or even z=6, bringing complementary information to the optical surveys. Since then, few dedicated instruments have been built (CHIME, Tianlai, BINGO) to explore the feasibility of the method; Other more ambitious instruments, such as HIRAX, CHORD or BINGO will be commissioned in the coming years. Intensity mapping surveys are also envisaged for SKA, in addition to the classical HI source surveys. After presenting the principle of 21 intensity mapping, I will briefly discuss its cosmological promises, as well as some of the associated instrumental and scientific challenges. I will then present some of the results of ongoing observations, focusing on Tianlai, and on PAON4. Tianlai is an international project that operates two pathfinder instruments, a cylinder array and a parabolic array, built in Xinjiang, in western China. PAON4 is a small test interferometer, located in Nançay, used to explore some of the technical aspects of compact radio arrays, operating in transit mode.

Local contact: Réza ANSARI, organization: Frédéric GALLIANO





Archives:

           







Seminars in other places:

IAS, IAP, IAP/GRECO, IHES









Laboratoire AIM (Astrophysique, Instrumentation, Modélisation)
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Le Commissariat à l'énergie atomique et aux énergies alternatives
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Institut de Recherche sur les lois Fondamentales de l'Univers
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