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, Carlos GOMEZ-GUIJARRO, Denise LANZIERI.

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: March 31, 2023)


Tuesday

March 28

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

[TBA]



Local contact: Michel BERTHÉ, organization: Michel BERTHÉ

Tuesday

April 4

10:00
Andrei IGOSHEV
(University of Leeds)

Magneto-thermal evolution of neutron stars


[click here for abstract]
We perform first three-dimensional simulations of the magneto-thermal evolution using a spectral MHD code for crust confined magnetic field configurations. Our results show that presence of strong toroidal magnetic field in magnetars is necessary to explain their quiescent thermal emission, in particular a formation of a single hot spot. Using our thermal maps we are able to explain light curves of 10 out of 19 magnetars in quiescence. In the case of the central compact objects, we test the configuration of magnetic field formed as a result of stochastic dynamo. Such a magnetic field consists of multiple randomly orientated loops of magnetic field. Surface thermal map is becoming patchy and includes multiple hot and cold regions which are always observed simultaneously. The global dipolar field slowly formed as a result of the Hall and Ohmic evolution. In our simulations we see 5-10% pulsed fraction and difference of two times in temperature between hot and cold regions typical for observations of the central compact objects. We also study off-centred dipole configurations and found that they decay over time.

Local contact: Raphaël RAYNAUD, organization: Frédéric GALLIANO
Tuesday

April 11

10:00
Anne VERHAMME
(Université de Genève)

Searching for the sources of Cosmic Reionisation


[click here for abstract]
Over the past 5 years, we have made tremendous progress on both direct detections of the escape of ionizing radiation from galaxies, over a broad range of redshifts (and instruments), and the tests and validations of indirect probes of the escape of ionizing radiation from galaxies, both from observations and simulations. I will review these recent achievements, and describe the next steps to understand the nature of the sources of reionisation.

Local contact: Vianney LEBOUTEILLER, organization: Frédéric GALLIANO






Archives:

            





2023

Tuesday

January 10

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

20 years of MegaCam scientific operations on the Canada-France-Hawaii Telescope


[click here for abstract]
Over its history CFHT has helped build or hosted dozens of instruments, operating from ultraviolet to mid-infrared wavelengths, attuned to Maunakea’s renowned observing conditions. One instrument, though, eclipses them all – MegaCam. It is in fact hard to imagine CFHT’s success today without the decisions made two decades ago to build what was then the largest digital focal plane in the world. MegaCam took engineering techniques to closely mount CCDs into a single camera to a whole new level. With its 1 degree field of view, MegaCam was able to tile the sky with images, creating rich and precise datasets on enormous scales that could be mined by the entire scientific community for decades. To date MegaCam has led to more peer reviewed science publications than all other instruments used at CFHT combined. It has been used to tune the model of Dark Energy and map vast regions of Dark Matter, unveil faint wisps of stars flung from interacting galaxies, reveal hundreds of free floating planets in star forming regions, and is currently directly contributing to a Stage IV dark energy measurement by providing the key ground-based photometry for the ESA Euclid space mission to derive photometric redshifts of hundreds of millions of galaxies over the northern sky. All of this is part of a revolution in wide field high-resolution optical imaging that CFHT pioneered for many years. Three speakers will offer a complete overview from technical aspects to the most impactful scientific result over these past two decades: - Stephan Aune (CEA, SEDI) - Design and construction by CEA Paris-Saclay - Jean-Charles Cuillandre (CEA, DAp) - Scientific operation at CFHT - Pierre Astier (IN2P3, LPNHE) - Supernovae and the Dark Energy equation-of-state

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

January 17

10:00
Ludovic PETITDEMANGE
(LRA/LERMA)

Dynamo action and angular momentum transport in simulated stellar radiative zones


[click here for abstract]
The evolution of a star is influenced by its internal rotation dynamics through transport and mixing mechanisms, which are poorly understood. Magnetic fields can play a role in transporting angular momentum and chemical elements, but the origin of magnetism in radiative stellar layers is unclear. Using global numerical simulations, we identify a subcritical transition to turbulence due to the generation of a magnetic dynamo. Our results have many of the properties of the theoretically-proposed Tayler-Spruit dynamo mechanism, which strongly enhances transport of angular momentum in radiative zones. It generates deep toroidal fields that are screened by the stellar outer layers. This mechanism could produce strong magnetic fields inside radiative stars, without an observable field on their surface. Magnetic fields generated by dynamo action appear as a process to trigger turbulence in stellar interiors. Depending on the parameters or initial conditions, we report different dynamo branches that could explain stellar magnetism and the rotation profiles observed for stars having a thick radiative envelope.

Local contact: Raphaël RAYNAUD, organization: Raphaël RAYNAUD
Tuesday

January 24

10:00
[TBA]
Tuesday

January 31

10:00
Cancelled / séminaire annulé
Julien AUBERT
(IPGP)

Variations géomagnétiques rapides: un nouveau message émis par le noyau de la Terre


[click here for abstract]
Le signal géomagnétique est une source riche d’informations sur la structure, la dynamique interne et l’histoire de notre planète. La production du champ magnétique Terrestre par effet dynamo dans le noyau externe implique une large disparité d’échelle spatiales et plus spécifiquement temporelles, s’étalant sur une gamme allant de l’année au milliard d’années. Depuis la mise en place d’observatoires magnétiques à la surface émergée de la Terre, l’attention s’est portée sur l’explication des variations à l’échelle du siècle, qui sont liées aux mouvements de convection dans le noyau. Depuis une vingtaine d’années, une couverture satellitaire globale et continue a cependant mis en évidence des variations de l’année à la dizaine d’années, dont l’origine est débattue. Ces nouvelles données ouvrent une fenêtre sur des phénomènes magnétohydrodynamiques rapides, de nature ondulatoire, en interaction avec la convection lente dans le noyau. Dans cet exposé, je présenterai les défis posés par la simulation conjointe des deux phénomènes ainsi que les avancées récentes et applications géophysiques potentielles.

Local contact: Sacha BRUN, organization: Frédéric GALLIANO
Tuesday

February 7

10:00
[TBA]
Tuesday

February 14

10:00
Special event / Evénement exceptionnel
Assemblée générale
(Irfu)

_



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

February 21

Vacations / Vacances
Vacances d'hiver
Tuesday

February 28

Vacations / Vacances
Vacances d'hiver
Tuesday

March 7

10:00
Cancelled / séminaire annulé
Stefano CAMERA
(Università degli Studi di Torino)

Cosmology with the SKA Observatory and its Precursors/Pathfinders


[click here for abstract]
In this talk, I shall review the most peculiar aspects of cosmology in the radio band, with a special focus on the SKA Observatory (SKAO). I shall present the main radio probes that can be exploited for late-time cosmology: continuum and 21-cm line galaxy surveys, neutral hydrogen intensity mapping, and weak lensing cosmic shear at radio frequencies. Furthermore, I shall present the most recent analyses of actual data from SKAO's pathfinders and precursors. Moreover, I shall discuss the added value of multi-wavelength synergies, presenting some show-case example of the power of radio-optical cross-correlations to test the foundations of the concordance cosmological model, such as the nature of dark matter and dark energy, or tests of inflation and gravity.

Local contact: Denise LANZIERI, organization: Denise LANZIERI
Tuesday

March 14

10:00
Marie GUÉGUEN
(Université de Rennes)

Cosmology: a tension within code comparisons


[click here for abstract]
Code comparisons in cosmology are often performed with the underlying objective of identifying predictions upon which different codes converge that can be interpreted as robust, free of artifacts, predictions. Such an objective assumes that code comparisons can be constructed in such a way that the two notions of convergence and of robustness collapse. But, in order to achieve such a goal, code comparisons of structure formation have to meet an important epistemic challenge: that of constructing their codes ensemble on the basis of codes that are as independent as possible, but also comparable. In this talk, I show that enforcing the latter often amounts to multiplying common idealizations that hinder the achievement of the former, and thus leads to code comparisons that include many unscrutinized sources of artefacts possibly similarly distorting the predictions of the model. As a result, I argue that in context of high uncertainties where the domain of verification and validation of simulations has shrunk to code comparisons, code comparisons are better and actually very efficient as exploratory tools, both for getting insights into the physics implemented and for breaking the epistemic opacity of numerical simulations.

Local contact: Frédéric GALLIANO, organization: Frédéric GALLIANO
Tuesday

March 21

10:00
Cancelled / séminaire annulé
Francisca KEMPER
(Institute of Space Sciences (ICE-CSIC) / ICREA / IEEC, Spain)

The interstellar dust reservoir in galaxies


[click here for abstract]
The evolution of interstellar dust reservoirs, and the evolution of galaxies themselves go hand-in-hand, as the presence of dust alters evolutionary drivers, such as the interstellar radiation field and the star formation history, while at the same time, the dust is being formed and altered by processes taking place in galaxies. However, far-infrared and submillimeter studies have revealed enormous dust masses at high redshifts that are difficult to explain with dust production from evolved stars (the so-called "dust budget problem"), while in the nearby universe there is also a significant mismatch between the dust production rate and the dust mass observed in the interstellar medium of galaxies. I will go over some possible explanations in an attempt to find a way forward towards a solution to this seeming discrepancy.

Local contact: Frédéric GALLIANO, organization: Frédéric GALLIANO
Tuesday

March 28

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

[TBA]



Local contact: Michel BERTHÉ, organization: Michel BERTHÉ
Tuesday

April 4

10:00
Andrei IGOSHEV
(University of Leeds)

Magneto-thermal evolution of neutron stars


[click here for abstract]
We perform first three-dimensional simulations of the magneto-thermal evolution using a spectral MHD code for crust confined magnetic field configurations. Our results show that presence of strong toroidal magnetic field in magnetars is necessary to explain their quiescent thermal emission, in particular a formation of a single hot spot. Using our thermal maps we are able to explain light curves of 10 out of 19 magnetars in quiescence. In the case of the central compact objects, we test the configuration of magnetic field formed as a result of stochastic dynamo. Such a magnetic field consists of multiple randomly orientated loops of magnetic field. Surface thermal map is becoming patchy and includes multiple hot and cold regions which are always observed simultaneously. The global dipolar field slowly formed as a result of the Hall and Ohmic evolution. In our simulations we see 5-10% pulsed fraction and difference of two times in temperature between hot and cold regions typical for observations of the central compact objects. We also study off-centred dipole configurations and found that they decay over time.

Local contact: Raphaël RAYNAUD, organization: Frédéric GALLIANO
Tuesday

April 11

10:00
Anne VERHAMME
(Université de Genève)

Searching for the sources of Cosmic Reionisation


[click here for abstract]
Over the past 5 years, we have made tremendous progress on both direct detections of the escape of ionizing radiation from galaxies, over a broad range of redshifts (and instruments), and the tests and validations of indirect probes of the escape of ionizing radiation from galaxies, both from observations and simulations. I will review these recent achievements, and describe the next steps to understand the nature of the sources of reionisation.

Local contact: Vianney LEBOUTEILLER, organization: Frédéric GALLIANO
Tuesday

April 18

10:00
Judith IRWIN
(Queen's University, Canada)

CHANG-ES — Past and Future


[click here for abstract]
CHANG-ES (Continuum Halos in Nearby Galaxies — an EVLA Survey) is a project to observe 35 nearby galaxies that are edge-on to the line of sight to focus on their radio halos and the disk-halo connection. Wide-band VLA observations at L-band (1.5 GHz) and C-band (6.0 GHz) have provided opportunities to study in-band spectral indices, and observations in all four Stokes parameters with Rotation Measure Synthesis has led to a new understanding of the structure of kpc-scale magnetic fields in disk galaxies. This talk will highlight some of the results of the project and look to the future, as newly completed S-band (3.0 GHz) observations have filled in the L-band to C-band gap and led to the widest contiguous frequency coverage yet seen for galaxies.

Local contact: Suzanne MADDEN, organization: Frédéric GALLIANO
Tuesday

April 25

Vacations / Vacances
Vacances de printemps
Tuesday

May 2

Vacations / Vacances
Vacances de printemps
Tuesday

May 9

10:00
Thomas HENNING
(Max Planck Institute for Astronomy, Heidelberg)

[TBA]



Local contact: Frédéric GALLIANO, organization: Frédéric GALLIANO
Tuesday

May 16

10:00
Julien AUBERT
(IPGP)

Variations géomagnétiques rapides: un nouveau message émis par le noyau de la Terre


[click here for abstract]
Le signal géomagnétique est une source riche d’informations sur la structure, la dynamique interne et l’histoire de notre planète. La production du champ magnétique Terrestre par effet dynamo dans le noyau externe implique une large disparité d’échelle spatiales et plus spécifiquement temporelles, s’étalant sur une gamme allant de l’année au milliard d’années. Depuis la mise en place d’observatoires magnétiques à la surface émergée de la Terre, l’attention s’est portée sur l’explication des variations à l’échelle du siècle, qui sont liées aux mouvements de convection dans le noyau. Depuis une vingtaine d’années, une couverture satellitaire globale et continue a cependant mis en évidence des variations de l’année à la dizaine d’années, dont l’origine est débattue. Ces nouvelles données ouvrent une fenêtre sur des phénomènes magnétohydrodynamiques rapides, de nature ondulatoire, en interaction avec la convection lente dans le noyau. Dans cet exposé, je présenterai les défis posés par la simulation conjointe des deux phénomènes ainsi que les avancées récentes et applications géophysiques potentielles.

Local contact: Sacha BRUN, organization: Frédéric GALLIANO
Tuesday

May 23

10:00
James DUNLOP
(University of Edinburgh)

[TBA]



Local contact: Carlos GÓMEZ-GUIJARRO, organization: Carlos GÓMEZ-GUIJARRO
Tuesday

May 30

10:00
Stefanie WALCH-GASSNER
(University of Köln)

[TBA]



Local contact: Suzanne MADDEN, organization: Frédéric GALLIANO
Tuesday

June 6

10:00
[TBA]
Tuesday

June 13

10:00
[TBA]
Tuesday

June 20

10:00
Special event / Evénement exceptionnel
Semaine de la SF2A
[TBA]
Tuesday

June 27

10:00
[TBA]
Tuesday

July 4

10:00
Werner BECKER
(MPE)

[TBA]



Local contact: Fabio ACERO, organization: Frédéric GALLIANO
Tuesday

July 11

Vacations / Vacances
Coupure estivale
Tuesday

September 5

10:00
[TBA]
Tuesday

September 12

10:00
[TBA]
Tuesday

September 19

10:00
[TBA]
Tuesday

September 26

10:00
[TBA]
Tuesday

October 3

10:00
[TBA]
Tuesday

October 10

10:00
[TBA]
Tuesday

October 17

10:00
[TBA]
Tuesday

November 7

10:00
[TBA]
Tuesday

November 14

10:00
[TBA]
Tuesday

November 21

10:00
[TBA]
Tuesday

November 28

10:00
[TBA]
Tuesday

December 5

10:00
[TBA]
Tuesday

December 12

10:00
[TBA]





Archives:

            







Seminars in other places:

IAS, IAP, IAP/GRECO, IHES









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