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: May 23, 2022)


Tuesday

May 17

10:00
Recent hire 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)

SVOM/MXT



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 hire 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)

SVOM/MXT



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

June 21

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

[TBA]



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)

[TBA]



Local contact: Jérôme RODRIGUEZ, organization: Matteo BUGLI
Tuesday

September 13

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

[TBA]



Local contact: Anaëlle MAURY, organization: Frédéric GALLIANO
Tuesday

September 27

10:00
Elisa COSTANTINI
(SRON, Netherlands)

[TBA]



Local contact: Anne DECOURCHELLE, organization: Frédéric GALLIANO
Tuesday

October 4

10:00
[TBA]
Tuesday

October 18

10:00
[TBA]
Tuesday

November 15

10:00
Anaëlle MAURY
(LFEMI)

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



Local contact: Anaëlle MAURY, organization: Frédéric GALLIANO
Tuesday

November 29

10:00
[TBA]
Tuesday

December 13

10:00
[TBA]





Archives:

           







Seminars in other places:

IAS, IAP, IAP/GRECO, IHES









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