PhD subjects

Dernière mise à jour : 31-08-2016

24 sujets IRFU

«««

• Astrophysics

24 réponse(s)

Understanding dark energy by mapping through time and space the dark matter in the Universe revealed by weak gravitational lensing: measurement of peaks to constrain cosmological parameters

SL-DSM-16-0119

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Martin Kilbinger

Starting date : 01-09-2016

Contact :

Martin Kilbinger

CEA - DSM/IRFU/SAp/LCS

01 69 08 17 53

Thesis supervisor :

Martin Kilbinger

CEA - DSM/IRFU/SAp/LCS

01 69 08 17 53

More : www.cosmostat.org/kilbinger

More : www.cosmostat.org/kilbinger

Weak gravitational lensing, the distortion of the images of high-redshift galaxies due to foreground matter structures on large scales is one of the most promising tools of cosmology to probe the dark sector of the Universe. To quantify the distortions induced on background galaxy images by matter structures, we have to accurately measure their shapes. Shape measurements to a few percent accuracy of typically small, faint, and low-SNR galaxy images that are blurred by the PSF (point-spread function) of the optical imaging system is one of the biggest challenges of weak gravitational lensing.



This PhD work is an important step towards the cosmological analysis of large data sets to advance our understanding of dark energy.

The goal of this PhD is to perform a weak-lensing analysis on optical wide-field imaging data, and to use the measured shapes of background galaxies to obtain weak-lensing maps of the mass on very large scales. From these maps, peak count statistics are computed to infer cosmological parameters, including the dark energy parameter w.



State-of-the-art image processing and statistical techniques will be employed that are being developed in the inter-disciplinary CosmoStat laboratory. These techniques will be applied to very large and deep optical ground-based galaxy surveys led by SAp as a milestone towards the European space mission Euclid. This thesis is conducted within the Euclid consortium, in which CEA has leading

roles, to contribute to the preparation of this ultimate cosmological probe.

Accretion-ejection coupling in microquasars

SL-DSM-16-0932

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Stéphane CORBEL

Starting date : 01-09-2016

Contact :

Stéphane CORBEL

Université Paris 7 - DRF/IRFU/SAP/LEPCHE

01 69 08 45 62

Thesis supervisor :

Stéphane CORBEL

Université Paris 7 - DRF/IRFU/SAP/LEPCHE

01 69 08 45 62

Euclid weak lensing: PSF and galaxy shape measurements and the impact of errors on cosmological parameters

SL-DSM-16-0032

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Jean-Luc STARCK

Starting date : 01-10-2016

Contact :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Thesis supervisor :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

More : http://jstarck.cosmostat.org

More : http://www.cosmostat.org

The Euclid satellite, to be launched in 2020, will observe the sky in the optical and infrared, and will be able to map large scale structures and weak? lensing distortions out to high redshifts. Weak gravitational lensing is thought to be one of the most promising tools of cosmology to constrain models. Weak lensing probes the evolution of dark-matter structures and can help distinguish between dark energy and models of modified gravity. Thanks to the shear measurements, we will be able to reconstruct a dark matter mass map of 15000 square degrees. These shear measurements are derived from the galaxy shapes, which are blurred by the PSF (point-spread function) of the optical imaging system. One of the main problems to achieve the scientific goals is therefore the need to model the point spread function (PSF) of the instrument with a very high accuracy. The PSF field can be estimated from the stars contained in the acquired images. It has to take into account the spatial and spectral variation of the PSF. An additional problem to take care of is the subsampling of the images. Once the PSF is correctly modelled, we need to derive the shear from galaxy shapes.



The goal of the PhD consists first in finding a robust method to build the 3D PSF field (two spatial and one spectral dimensions) using interpolations tools on the adequate manifold. As this manifold is unknown, it has to be learned using recent learning techniques based on sparse data representation. The PSF field can then be used as ingredient for galaxy shape measurements. Both PSF estimation and shape measurement have some limitations, and are affected by statistical and systematic errors. An important step will be the study of the propagation of these errors from measurements to cosmological parameters.

Dynamical evolution of stars: MHD modeling of the internal angular momentum transport processes

SL-DSM-16-0765

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Dynamique des Etoiles et de leur Environnement (LDEE)

Saclay

Contact :

Allan Sacha BRUN

Stéphane MATHIS

Starting date : 01-10-2016

Contact :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

Thesis supervisor :

Stéphane MATHIS

CEA - DSM/IRFU/SAp/LDEE

0169084930

More : http://lcd-www.colorado.edu/sabrun/

More : http://irfu.cea.fr/Sap/LDEE/LDEE_web/index.html

More : http://sfmathis.free.fr/Home.html

Stars are dynamical rotating, magnetic, turbulent objects. Breakthroughs are now obtained for our knowledge of their internal dynamics thanks to observational constraints obtained by high-precision helio- and asteroseismology for the Sun and stars respectively. Indeed, observed internal rotation profiles show that they are the seats of strong and efficient angular momentum transport mechanisms all along their evolution from their birth to their death. To explain these observations, two mechanisms in convectively stable stellar radiation regions, which drive the secular rotational evolution of stars, are proposed: internal gravity waves, magnetic fields and their interactions with differential rotation, large-scale meridional flows and turbulence (e.g. Talon & Charbonnel 2005; Strugarek, Brun & Zahn 2011). These mechanisms deeply impact the evolution of stars, which have a broad impact on their planetary and galactic environment.



The main objective of this PhD project is to build realistic modelling of internal angular momentum transport mechanisms in stars using synergies between advanced semi-analytic methods devoted to the study of the impact of dynamical processes on secular time scales and of 3D ASH numerical simulations computed on High Performance Computing large facilities (CCRT) which allow us to study 3D and nonlinear MHD mechanisms in stars. New 2D secular equations, ab-initio scaling laws and prescriptions will be obtained. A peculiar effort will be done for the study of internal gravity waves, driven by the restoring buoyancy force, modified simultaneously by differential rotation and magnetism (also called magneto-gravito-inertial waves), which are excited by turbulent convective motions at radiation/convection interfaces, and on their breaking. It will benefit of our recent advances obtained simultaneously thanks to global 3D nonlinear ASH simulations of the Sun (Brun, Miesch & Toomre 2011; Alvan, Brun & Mathis 2014) and of 3D asymptotic theoretical models allowing their detailed analysis (Alvan et al. 2015). This allowed us to compute waves spectrum, amplitude, damping and visibility. However, these studies should now be generalized in a systematic way for all low mass and intermediate-mass stars (from K to A type stars) all along their evolution (e.g. Browning, Brun & Toomre 2004; Fuller et al. 2014; Lee, Neiner & Mathis 2014). In this framework, it will be necessary to characterize waves dynamics for all possible stratification, rotation, shear and magnetic field intensity (e.g. Mathis & de Brye 2012; Mathis, Neiner & Tran Minh 2014) to compute their spectrum, amplitude, damping, visibility and induced transport of angular momentum. This work will allow us to give scaling laws and parameters diagram mandatory to interpret current and future helio- and asteroseismic data (SOHO, CoRoT, Kepler/K2 and TESS & PLATO) to obtain a general understanding of the dynamical evolution of stars. This PhD project is part of the ERC project SPIRE (Stars: Dynamical Processes driving tidal Interactions, Rotation and Evolution; PI: S. Mathis).



Alvan, Brun & Mathis 2014, A&A, 565, 42

Alvan, Strugarek, Brun, Mathis & Garcia 2015, A&A, 581, 112

Brun, Miesh & Toomre 2011, ApJ, 742, 79

Browning, Brun & Toomre 2004, ApJ, 601, 512

Fuller et al. 2014, ApJ, 796, 17

Lee, Neiner & Mathis 2014, MNRAS, 443, 1515

Mathis & de Brye 2012, A&A, 540, 37

Mathis, Neiner & Tran Minh 2014, A&A, 565, 47

Strugarek, Brun & Zahn 2011, A&A, 532, 34

Talon & Charbonnel 2005, A&A, 440, 981
Cosmic Rays in Superbubbles

SL-DSM-16-0814

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Isabelle GRENIER

Starting date : 01-09-2016

Contact :

Isabelle GRENIER

Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

Thesis supervisor :

Isabelle GRENIER

Université Paris Diderot - DSM/IRFU/SAp/LEPCHE

01 69 08 44 00

More : http://irfu.cea.fr/Sap/

More : http://www.nasa.gov/mission_pages/GLAST/news/cygnus-cocoon.html

A century-long standing problem is to explain how cosmic rays are accelerated to relativistic energies and how they diffuse in their host galaxy. Notable progress has been made on their production in supernova remnants, but the recent discovery in gamma rays, with the Fermi satellite, of a cocoon of fresh and energetic cosmic rays in the Cygnus X superbubble has disclosed an important new facet of the problem: what is the impact on particle (re-)acceleration and diffusion of the large level of turbulence generated in the superbubble medium by the activity of its numerous massive stars? Can this turbulent phase significantly modify our current views on cosmic-ray transport in the Galaxy because most cosmic-ray sources are to be found in active, turbulent starburst regions? http://www.nasa.gov/mission_pages/GLAST/news/cygnus-cocoon.html

We propose to compare two superbubbles of different age and energy density: the extreme case of the few-million-year old, bursting Cygnus X bubble, which hosts several stellar clusters and the Cygnus OB2 supercluster; and the older, more frequent, but less energetic case of the Orion-Eridanus superbubble near the Sun. We propose to combine expertise on cosmic-ray transport/acceleration, on gamma-ray observations of cosmic rays, and on multi-wavelength observations of the interstellar medium in these bubbles, in order to test a new acceleration mechanism and to revisit the impact of the turbulent bubble medium on different observational cosmic-ray diagnostics, Galactic-wide and locally. The comparison of the two superbubbles will serve for future statistical studies of the impact of starburst regions on the cosmic-ray content of a galaxy, therefore on the importance of cosmic rays in the early development of galaxies.



The project aims at a quantitative modelling of cosmic-ray acceleration, transport, and radiation in the two relatively well-known superbubbles. It includes complementary tasks: (i) a detailed account of the interstellar conditions and particle losses in the bubbles; (ii) an assessment of the stellar wind and supernova activity in these young starburst regions; (iii) the derivation of average cosmic-ray spectra for random shocks in the bubbles, for two injection sources (in-situ injection and injection of outer Galactic cosmic rays); (iv) comparisons with the available gamma-ray data. Task (iii) will be developed in close collaboration with Prof. R. Schlickeiser in Germany.

This project has been accepted as an International France-Germany Collaborative Research Project (ANR – DFG). It builds on the experience and complementary expertise on multi-wavelength interstellar tracers and the discovery of the gamma-ray signal from superbubbles at CEA-Saclay/Irfu/AIM (I. Grenier, J. M. Casandjian, D. Marshall); and on advanced cosmic-ray acceleration theory at the Bochum University in Germany (R. Schlickeiser, A. Stockem). The French thesis advisor, I. Grenier, has successfully led or co-led 15 PhD thesis in high-energy astrophysics.

The PhD student will benefit from exposure to advanced theoretical calculations as well as to state-of-the-art multi-wavelength observations. This is a clear strength for future research with the future CTA TeV observatory, which will devote guaranteed time to observations of starburst regions. The focus on low cosmic-ray energies will also serve them as the high-energy community looks forward to a soft gamma-ray observatory in the next decade.

SL-DSM-16-0019

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Jérôme RODRIGUEZ

Starting date : 01-10-2016

Contact :

Jérôme RODRIGUEZ

CEA - DSM/IRFU/SAp/LEPCHE

01 69 08 98 08

Thesis supervisor :

Jérôme RODRIGUEZ

CEA - DSM/IRFU/SAp/LEPCHE

01 69 08 98 08

Study of ablation front for laser plasma experiment of stellar opacity measurement

SL-DSM-16-0179

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Astrophysique Nucléaire-Plasmas Stellaires

Saclay

Contact :

Jean-Eric DUCRET

Starting date : 01-10-2016

Contact :

Jean-Eric DUCRET

CEA - DSM/IRFU/SAp/LMPA

0540002582

Thesis supervisor :

Jean-Eric DUCRET

CEA - DSM/IRFU/SAp/LMPA

0540002582

The proposed doctorate thesis is to be done within the framework of a project aiming at testing the technique of double ablation front to heat and compress targets on an experiment to be performed in 2016 at the LLE/OMEGA laser facility in Rochester, USA. Our project is motivated by recent results of seismic investigations of stellar interiors, which have put in evidence inconsistencies in the stellar evolution models and in the laboratory experiments. We intend, following the hydrodynamics simulations we performed to design opacity experiments with the double ablation front technique in planar geometry. If successful, this experiment will serve as a basis for LMJ-PETAL proposals. The student will take part in the preparation of the experiment by running hydrodynamics simulations in the chosen experimental configuration to be done with the CHIC code (CELIA Hydrodynamics & Implosion Code), which will help designing the targets to be used. Afterwards, he/she will take part in the running of the experiment and do the data analysis and interpretation. The physics interpretation of the experiment will be done within the framework of plasma atomic physics models.
Construction of a spectrograph and quasar target selection for the Dark Energy project, DESI

SL-DSM-16-0250

Research field : Astrophysics

Location :

Service de Physique des Particules (SPP)

Groupe Bao

Saclay

Contact :

Christophe Magneville

Christophe YECHE

Starting date : 01-10-2016

Contact :

Christophe Magneville

CEA - DSM/IRFU/SPP/Bao

01-69-08-33-44

Thesis supervisor :

Christophe YECHE

CEA - DSM/IRFU/SPP/Bao

01-69-08-70-50

Acceleration of Universe expansion is one the main topics of modern cosmology. It can stem from a new component, dark energy, which corresponds to 70% of the energy content of Universe. To study its nature and its equation of state, one can measure a standard ruler given by baryonic acoustic oscillation (BAO) frequency for various redshift universe slices. This approach was used successfully for the first time in 2005 by the Sloan Sky Digital Survey (SDSS). This positive observation was confirmed in 2012 by BOSS project (SDSS-III) both with galaxies and HI absorbers in quasar spectra. Our group of Irfu/SPP is currently involved in the analysis of BOSS and eBOSS observations.



Our group prepare the next generation of experiments studying BAO by building the spectrograph of the new program, DESI. This project will perform a 3D survey of millions of galaxies and quasars with the 4-meter Mayall telescope in Arizona (USA).



The graduate will work on the spectrograph in collaboration with our industrial partner (WINLIGHT) and our academic partners (Aix-Marseille University and Berkeley University). In parallel, he/she will develop algorithms for the quasar target selection. These methods will be tested with pilot surveys at AAT telescope (Australia) and at MMT telescope (USA). Finally, in 2019, he/she will observe with DESI the first spectra of the quasar targets.

Study of a compact (sub)millimeter imaging spectrometer for observational cosmology

SL-DSM-16-0736

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Vincent REVERET

Louis RODRIGUEZ

Starting date : 01-09-2016

Contact :

Vincent REVERET

CEA - DSM/IRFU/SAp/LSIS

01 69 08 74 02

Thesis supervisor :

Louis RODRIGUEZ

CEA -

More : http://irfu.cea.fr/Sap/

One of the future challenges in instrumentation for cosmology is the detection of certain polarization modes (called B-modes) of the cosmic microwave background from the ground or from space. This discovery would constrain many cosmological parameters, explain inflation and prove the existence of gravitational waves. To detect this very weakly polarized signal, the instruments must be both highly sensitive and should also facilitate the subtraction of “parasitic” foregrounds, mainly of galactic origin. To effectively characterize and then subtract these foregrounds, observations must be multi-wavelength (twenty bands between 500 microns and 5 mm wavelength).

CEA through the Service d'Astrophysique (SAp) in Saclay and LETI in Grenoble develops ultra-sensitive cryogenic bolometers for measuring the polarized (sub)millimeter radiation. The purpose of this thesis is the complete study and experimental validation of the spectroscopic capacity of such detectors, as well as the treatment of associated data. The instrumental method is completely new in this area: it is based on an interferometric system arranged directly within the pixels. Ultimately, it will be possible to obtain an ultra-compact imaging spectrometer with medium spectral resolution ("spectrometer on a chip"), perfectly suited to the constraints of a space mission. The student will be supervised by a team of physicists, experts in microelectronics at LETI and experimentalist physicists for modeling and cryogenic tests SAp. These studies pave the way for instrumentation in other fields in astrophysics and can generate more applied developments in medical imaging or in the field of control security in TeraHertz band. This project is partially funded by the FOCUS labex and supported by CNES.

The role of Supermassive Black Holes in Galaxy Evolution

SL-DSM-16-0868

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Stephanie JUNEAU

Starting date : 01-10-2016

Contact :

Stephanie JUNEAU

CEA - DSM/IRFU/SAp/LCEG

Thesis supervisor :

Stephanie JUNEAU

CEA - DSM/IRFU/SAp/LCEG

More : http://irfu.cea.fr/Pisp/stephanie.juneau/

More : http://irfu.cea.fr/Sap/

Cosmological analysis of the XXL cluster survey

SL-DSM-16-0555

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Marguerite PIERRE

Starting date : 01-10-2016

Contact :

Marguerite PIERRE

CEA - DSM/IRFU/SAp/LCEG

0169083492

Thesis supervisor :

Marguerite PIERRE

CEA - DSM/IRFU/SAp/LCEG

0169083492

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=972

More : http://irfu.cea.fr/xxl

Clusters of galaxies are – along with supernovae, CMB and baryonic acoustic oscillations – are a major probe for the various cosmological scenarios. In particular, cluster number counts are very sensitive to the Dark Energy equation of state that depends on the volume (geometrical effects) and on the growth rate of the structures (gravitational effect).



The thesis will take place within the framework of the XXL project, which is the largest extragalactic survey performed by XMM (50 deg2), the X-ray satellite of the European Space Agency. The ultimate goal is toe constrain the dark energy equation of state using the some 500 clusters of galaxies newly discovered in the survey. In addition to the X-ray band, numerous observations are available in other wavebands (infrared, optical, millimetre, radio) as well as high-resolution numerical simulations. The XMM observations were performed from 2011 to 2013 and the first publications involving limited bright samples are due by then end of 2015.



The proposed thesis work will take place during the (critical) second phase of the project and consists in a detailed study of the parameters impacting on the cosmological analysis. This regards especially the evolution of the cluster physical properties that influence their detection as well as their mass estimates. The final goal will be to adequately model these factors in the global cosmological analysis, extending the current results with 100 clusters to the complete sample of some 500 clusters.



Tools that will be used during the thesis work:

Cosmological and cluster evolutionary models; X-ray pipeline; multi-wavelength observations of clusters; results from numerical simulations. All is available and the student will have to get rapidly acquainted to them.



Working context: worldwide consortium gathering some 100 scientists and organised in well-defined sub-projects.

http://irfu.cea.fr/xxl

See page ‘publications’ for detailed presentations of the XXL early results at international conferences.



We are seeking excellent candidates and having a good practice of English

Tracing back the cosmic history of galaxy formation with the large ALMA interferometer

SL-DSM-16-0015

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

David ELBAZ

Starting date : 01-10-2016

Contact :

David ELBAZ

CEA - DSM/IRFU/SAp

0169085439

Thesis supervisor :

David ELBAZ

CEA - DSM/IRFU/SAp

0169085439

More : http://david.elbaz3.free.fr/science.html

More : http://irfu.cea.fr/Sap/

More : http://irfu.cea.fr/Sap/en/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=977

The growth of black holes and stellar mass in galaxies through cosmic time

SL-DSM-16-0097

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2016

Contact :

Emanuele DADDI

CEA - DSM/IRFU/SAp/LCEG

Thesis supervisor :

Emanuele DADDI

CEA - DSM/IRFU/SAp/LCEG

Observations in the local Universe have established that galaxies contain supermassive black holes with masses that are

about 1/1000th of the host galaxy. It is still unclear which mechanism is at the origin of this correlation, inducing

such a fine tuning of masses at so different spatial scales. This thesis will use observations at a variety of wavelengths

of galaxies at high redshifts to explore the co-existence of stellar mass growth (via star formation) and black hole growth

(via black hole accretion), and thus constrain related key physical processes at the time the correlation was put in place.

The distribution of star formation in galaxies through cosmic time is remarkably simple and well behaved, as shown by the

existence of tight relations between fundamental galaxy parameters like stellar masses, star formation and molecular hydrogen

content. On the other hand, when considering individual galaxies, the black hole accretion rate (as proved by X-ray luminosities)

does not correlate with any other galaxy properties. When instead considering large galaxy ensembles, our group

was first to show that correlations are present with stellar masses. The thesis project will expand the work along these lines,

in particular using mid-IR probes of black hole growth together with X-ray to include the most obscured phases which are still

unaccounted for, based on new ultra-deep IR catalogs with Herschel, Spitzer and submm facilities. We will explore if the ensemble

black hole to stellar mass ratio depend on key physical parameters like morphology, star formation mode (merging or quiescent),

and redshift, shedding light on the co-evolution (or lack there-of) of black holes and galaxies.

The work will be carried out using the deepest Herschel data which are available to us, publicly available facilities,

and proposing for telescope time for crucial missing ingredients. In addition, the candidate will be able to work

with deep ground based and space based spectroscopy to study high redshift galaxy emission lines. The candidate will gain the

necessary scientific and technical expertise to be able to competitively request telescope time with major forthcoming facilities

like the Atacama Large Millimeter Array and the new generation optical-mid-IR space telescope (JWST).

Characterization and performance optimization of the focal plane of the Microchannel X-ray Telescope on-board the space astronomy mission SVOM.

SL-DSM-16-0023

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Systèmes et Architectures Spatiales (LSAS)

Saclay

Contact :

Aline MEURIS

Bertrand CORDIER

Starting date : 01-10-2016

Contact :

Aline MEURIS

CEA - DSM/IRFU/SAp/LSAS

01 69 08 12 73

Thesis supervisor :

Bertrand CORDIER

CEA - DSM/Irfu/SAp

0169082792

More : http://irfu.cea.fr/Sap/index.php

SVOM is a Sino-French mission to be launched in 2021 to study the gamma-ray bursts (GRB), among the most violent and energetic events in the Universe. The Microchannel X-Ray Telescope under the scientific responsibility of CEA observes the X-ray afterglow of GRB detected by the gamma-ray monitor ECLAIRs and improves the localizations of the sources to transmit detection alerts to a network of ground-based telescopes.



This thesis in space instrumentation aims at evaluating and demonstrating the on-ground and on-board performance of the MXT focal plane based on a pnCCD in the context of the SVOM mission. Two main studies based on experiments, simulation and modeling work can be led in this area:

1. Evaluation of the in-orbit performance degradation of the detector due to space radiations, by preparing and leading an irradiation campaign in external test facilities. The data analysis can conclude on a predictive model and optimized operation scenarios to limit the dégradations or even partially recover from them.

2. Preparation of the calibration campaign of the flight models of the camera, by defining and developing innovative methods and experimental means to characterize the flight detector. The calibration plan could be run on the qualification model of the camera to produce response matrices that will be implemented in the instrument simulator for the science team.



After calibration of the stand-alone camera, the PhD student will take part in world premiere to the coupling of the camera with the optics and to performance tests of the complete instrument.

Explosion mechanism of core-collapse supernovae

SL-DSM-16-0620

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Théorie et de Modélisation

Saclay

Contact :

Thierry FOGLIZZO

Starting date : 01-09-2015

Contact :

Thierry FOGLIZZO

CEA - DSM/IRFU/SAp/LTM

01 69 08 87 20

Thesis supervisor :

Thierry FOGLIZZO

CEA - DSM/IRFU/SAp/LTM

01 69 08 87 20

More : http://irfu.cea.fr/Projets/SN2NS/

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=1250

Scientific context:

How do massive stars explode ?

Stars more massive than 10 Msol end their evolution with a supernova explosion which mechanism is still a theoretical mystery. Researchers would like to understand how the collapse of the iron core, accompanying the formation of a proto neutron star, is able to turn into the observed explosion. Theoretical progress over the last ten years has revealed that the spherical symmetry is broken by the development of hydrodynamical instabilities in the innermost 200km, during the second which follows the shock bounce. Those instabilities are responsible for an asymmetric explosion and the kick of the residual neutron star.

Proposed work:

This PhD work proposes to clarify the explosion mechanism by understanding the relation between the radial structure of the rotating stellar core and the asymmetric character of the explosion. The tools developed by the team at SAp for this study include analytical techniques, numerical modeling and a shallow water analogue.

Expected results:

Theoretical prediction of the explosion criterion of massive stars depending on their angular momentum and their radial structure.
Physical and statistical modelling of interstellar dust properties in the nearby universe

SL-DSM-16-0206

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d’études de la formation des étoiles et du milieu interstellaire

Saclay

Contact :

Frédéric Galliano

Suzanne MADDEN

Starting date : 01-10-2016

Contact :

Frédéric Galliano

CNRS - DSM/IRFU/SAp/LCEG

01 69 08 18 21

Thesis supervisor :

Suzanne MADDEN

CEA - DSM/IRFU/SAp/LCEG

01 69 08 92 76

Dust grains play a major role in the physics of the interstellar medium. They absorb and reemit in the infrared most of the radiated stellar power. Moreover, they are responsible for the gas heating in photodissociation regions (PDR) and serve as catalysts of numerous chemical reactions. Their properties (chemical composition, size distribution, etc.) are however currently poorly known. These uncertainties put caution on numerous aspects of our knowledge of the interstellar medium: mass estimates, PDR models, unreddening, etc. Refining our comprehension of dust is crucial to understand the life cycle of interstellar matter and its effect on galaxy evolution.



One of the approaches, to tackle these open questions, consists in studying the way the observed grain properties vary with the physical conditions they experience. The PhD thesis we propose is aimed at focussing on the properties of the smallest grains (with a radius smaller than ˜10 nm) and of polycyclic aromatic hydrocarbons (PAH). These interstellar medium components radiates out of equilibrium in the mid-infrared (˜5-40 µm), and are the carriers of numerous resonance bands. This study will focus on several nearby galaxies, including the Magellanic clouds. The interest of studying nearby galaxies rather than the interstellar medium of our own galaxy resides in the diversity of the physical conditions of the environments we can access (metallicity, stellar radiation field intensity, etc.).



Numerous studies have already been published on this subject. However, most of them were superficial. There remains many aspects to study: identifying and physically modeling several bands of solids in star forming regions, and the correlation of the properties of the main PAH bands with the physical conditions diagnosed thanks to the new Herschel data.



The thesis will have several aspects. First, the analysis of mid-infrared spectra, obtained with the satellite Spitzer. Most of these spectra are already reduced. Most of this first step will consist in critically selecting the spectra to study, and homogenizing the data. Then, quantifying the physical components, which is not trivial, will be performed in a sophisticated manner. We propose that the student will develop a hierarchical bayesian model for spectral decomposition, which will allow him a precise quantification of the uncertainties and of the correlations between physical parameters. This new tools and its meticulous application to the data is the guaranty of a precise and original interpretation of the physical processes in the studied regions.



This thematics is particularly relevant for planning the scientific objectives of the James Webb Space Telescope (JWST), which should be launched in 2018.

Multi-phase study of the interstellar medium in primitive environments

SL-DSM-16-0878

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d’études de la formation des étoiles et du milieu interstellaire

Saclay

Contact :

Vianney Lebouteiller

Suzanne MADDEN

Starting date : 01-09-2016

Contact :

Vianney Lebouteiller

Laboratoire AIM - UMR7158

+33-1-69-08-49-37

Thesis supervisor :

Suzanne MADDEN

CEA - DSM/IRFU/SAp/LCEG

01 69 08 92 76

More : http://www.myravian.fr/

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=973&onglet=2359

Galaxy evolution and star formation are controlled notably by physical and chemical processes directly linked to the interstellar medium (ISM). The ISM is an essential component of galaxies, subject to various heating mechanisms (ionization by UV & XR photons and by cosmic rays, photoelectric effect on dust grains, shock waves) and at the origin of new stellar generations in cold clouds.



The main thermal processes in the Milky Way ISM are relatively well constrained, but they remain largely unexplored in metal-poor galaxies. Such galaxies experienced a slow chemical enrichment since the formation of the first objects, and they can be fortunately observed in the Local Universe where they provide us with a crucial reference for primordial environments. The motivations at the heart of the project are the following, (1) identify the main energetic sources to interpret correctly the gas and dust radiative tracers, and (2) examine the star-formation process in primitive environments in order to understand the star-formation history of galaxies.



We will study the main ISM heating and cooling tracers in a large galaxy sample, so as to explore the influence of the environment (in particular metallicity, existence of super-stellar clusters, ultraluminous X-ray sources, ...) on the physical conditions and the associated (mostly spectroscopic) diagnostics. The ISM study ought to account consistently for all phases (ionized gas, neutral atomic and molecular gas, dust) and therefore uses all available wavelength domains. Thus, the project makes the connection between the immense legacy of the Hubble, Spitzer, and Herschel space telescopes and the advent of new observatories such as ALMA, NOEMA, SOFIA, or JWST.



The project will allow the student to develop a twofold expertise of observer and modeler. Concerning the data, recent observations with ALMA, SOFIA, and Hubble obtained by our team will be available. During the thesis, we will seek to complement this dataset with new propositions for ground- and space-based missions. We will also model the ISM by using the most realistic structure and topology possible, comprising HII regions, photodissociation regions, molecular clouds, and diffuse ISM. The student will also interact with many collaborators through various international consortia.



Upon PhD completion, the student will acquire a strong technical background (observations and databases), numerical background (data analysis and programming), and (astro-)physical background (elementary processes, general interpretation, and cosmological interpretation). A number of these expertise domains can be highlighted and emphasized for the preparation of future missions such as JWST, Athena, or SPICA, or in possible applications in numerical simulations.
Stellar feedback: a key process of our Universe

SL-DSM-16-0256

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire de Théorie et de Modélisation

Saclay

Contact :

Patrick Hennebelle

Starting date : 01-09-2016

Contact :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

Thesis supervisor :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

More : http://irfu.cea.fr/Projets/COAST/

The Magnetic Sun and Space Weather: characterizing the nonlinear coupling between the solar dynamo and wind

SL-DSM-16-0349

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Dynamique des Etoiles et de leur Environnement (LDEE)

Saclay

Contact :

Allan Sacha BRUN

Starting date : 01-10-2016

Contact :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

Thesis supervisor :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

More : http://www.stars2.eu

More : http://irfu.cea.fr/Sap/

This PhD will prepare the ESA Cosmic Vision Solar Orbiter mission for which the CEA provides the focal plane of the STIX instrument. The aim of Solar Orbiter is to understand how the Sun by its activity and intense magnetism and modulated 11-year cycle controls the heliosphere, the magnetic cocoon around it extending more than 100 AU. The subject is therefore to develop scientific interpretation of Solar Orbiter data (including STIX) based on high performance computing simulations (HPC) of the solar dynamo and his 11-year cycle and to link it with the surface magnetism such as the emergence of magnetic flux, flares (the subject of study of STIX) or wind.

Today more satellites constantly observe the Sun but they all lie in the ecliptic plane. The Solar Orbiter satellite will allow to observe the solar poles with a lot more details coming out of the plane of the ecliptic. Understanding the Sun and its influence on the environment therefore requires in this context to develop global models not just local ones. The ASH and PLUTO 3-D MHD parallel codes that we co-develop at LDEE are ideal to attack this problem head-on because they can accurately model the convection, magnetism, activity and the solar wind in full spherical geometry.

This PhD will couple for the first time in 3-D internal and external magnetohydrodynamics of the Sun by linking ASH and PLUTO codes. This will allow us to compute solar wind solutions with or without eruptive phenomena by calculating faithfully the evolution of the solar magnetism via dynamo action. Similar work has been done in 2-D (Pinto, Brun et al., 2011, Reville, Brun et al. 2015), it will be extended to 3-D as well as go from a quasi-static approach to a dynamical coupling one between convection, magnetism, flares and wind during a 11-year cycle which has never been done. This PhD will also ensure the scientific return and exploitation of Solar Orbiter and STIX data at CEA. Space weather is booming, and this PhD will help develop a better understanding of magnetism and solar activity by linking it to its internal origin.
Spatially resolved spectral analysis of supernova remnants in gamma-rays

SL-DSM-16-0767

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Fabio Acero

Starting date : 01-10-2016

Contact :

Fabio Acero

CEA - DSM/IRFU/SAp/LEPCHE

0169084705

Thesis supervisor :

Fabio Acero

CEA - DSM/IRFU/SAp/LEPCHE

0169084705

More : irfu.cea.fr/Sap

Supernova remnants, the remain of a stellar explosion, are thought to be one of the main source of Galactic cosmic-rays. Those sources have spatial extension up to a few degrees on the sky and can be studied in details spatially.

The goal of this thesis is to understand the impact of the environment on the process of particle acceleration in supernova remnants. In order to achieve this goal, the PhD candidate will develop tools to perform spatially resolved spectroscopic analysis in gamma rays using the data from the Fermi space telescope. Those methods will be used to disentangle the spectral components in the supernova remnants evolving in complex ambient medium. The tools developed in this thesis could also be implemented in the Cherenkov Telescope Array, the next generation of ground gamma-ray telescope.
Cosmology with galaxy clusters: from Planck to Euclid

SL-DSM-16-0375

Research field : Astrophysics

Location :

Service de Physique des Particules (SPP)

Groupe Cosmologie Millimétique

Saclay

Contact :

Jean-Baptiste Melin

Starting date : 01-09-2016

Contact :

Jean-Baptiste Melin

CEA - DSM/IRFU/SPP/Cosmo mm

01 69 08 73 80

Thesis supervisor :

Jean-Baptiste Melin

CEA - DSM/IRFU/SPP/Cosmo mm

01 69 08 73 80

In 2015, the Planck collaboration has published the measurements of cosmological parameters obtained from the full mission dataset. These results are based on the analysis of the primary anisotropies of the cosmic microwave background (CMB) at redshift z=1100 and on the distribution of galaxy clusters detected by the satellite between redshift z=1 and z=0.

The parameters determined from the CMB anisotropies are in very good agreement with those measured by the baryonic acoustic oscillations and the supernovae but are in conflict with the distribution of galaxy clusters. This conflict is shown in the figure below and is more or less critical depending on the assumed cluster mass scale. Two explanations are possible: the cluster mass could be 40% greater than the mass currently estimated with the X-ray satellites, or the standard model of cosmology could be incomplete.

In order to choose between the two different explanations, we have to improve the cosmological analysis with clusters to reduce systematic uncertainties.

One of the current major limitations of the cosmological analysis with clusters resides in its heart: the likelihood function. This function links the observed cluster catalogue to a cosmological model. In order to achieve this goal, one has to assume a scaling law, which relates observed cluster characteristics (their flux) to a theoretical quantity (their mass). Up to now, in the Planck analysis, this scaling law is determined with external data, independently to the likelihood, which bring some compatibility issues.

The proposed work consists in building a new likelihood for the cluster cosmological analysis, which bypasses this problem, in integrating internal flux and external mass measurements as inputs and provides as outputs both the cosmological parameters and the scaling law.

This new likelihood will be applied to Planck data first and then deployed in the Euclid context.
Coronal emission and space weather: from models to solar flares prediction

SL-DSM-16-0910

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Dynamique des Etoiles et de leur Environnement (LDEE)

Saclay

Contact :

Allan Sacha BRUN

Starting date : 01-10-2016

Contact :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

Thesis supervisor :

Allan Sacha BRUN

CEA - DSM/IRFU/SAp/LDEE

+33 1 69 08 76 60

More : http://www.stars2.eu

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=971

More : http://www.astro.umontreal.ca/~paulchar/grps/page_accueil.html

Solar magnetic activity has a direct impact on planet Earth and our technological society, through various hazards such as intense radiations, magnetic clouds and solar energetic particles (SEPs). Space weather is thus of upmost importance and we must develop ways of anticiapting such activity and its impact. This requires to develop advanced data assimilation techniques based on robust and physically based models of solar flares. This is the main goal of this thesis that will develop 3 complementary axis: 1) 3-D MHD models of solar eruptions and X-ray radiation in support of Solar Orbiter/STIX instrument; 2) self-critical avalanche models of solar flares coupled to a modern data assimilation technique to perform prediction of intense flaring events and 3) the use of solarsoft to get familiar with X-ray data by using first GOES and RHESSI and after 2018 Solar Orbiter/STIX data. The PhD will be done in collaboration between Dr. A.S. Brun (CEA-Saclay), Prof. P. Charbonneau (University of Montreal) and Dr. N. Vilmer (Observatory of Paris-Meudon).
BINARY SYSTEMS: FORMATION, EVOLUTION, ENVIRONMENT

SL-DSM-16-0018

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Sylvain CHATY

Starting date : 01-10-2016

Contact :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 69 08 43 85

Thesis supervisor :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 69 08 43 85

More : https://fr.linkedin.com/pub/sylvain-chaty/60/b57/66

More : http://irfu.cea.fr/Sap/

Over 70% of massive stars live in a stellar pair(Sana et al. 2012). Such binary systems have a major impact on their evolution, strongly influenced by the presence of a "companion" star, in particular through the transfer of material, angular momentum, and the existence of intense stellar winds (Chaty 2013). The fate of these pairs of massive stars is determined by the evolution of each component, the most massive collapsing first during the supernova explosion, forming a neutron star or a black hole (Tauris & van den Heuvel, 2006). This is the birth of a compact binary -a compact object orbiting its companion-, among the most fascinating objects in the Universe. The massive companion star continuously ejects a strong wind, and the compact object, bathing in this wind, attracts a portion that accumulates on the surface, heated to temperatures of millions of degrees, and emitting X-rays.

The aim of this PhD thesis is to study the formation of massive star couples, their evolution and their impact on their surroundings, potentially triggering new stellar formations. This study will be primarily done using observations from ESO's VLT, in a multi-wavelength context.
Calibration of asteroseismic relations through eclipsing binaries showing pulsations: application to field and planet host stars observed by CoRoT, Kepler and K2.

SL-DSM-16-0954

Research field : Astrophysics

Location :

Service d'Astrophysique

Laboratoire Dynamique des Etoiles et de leur Environnement (LDEE)

Saclay

Contact :

Rafael A. Garcia

Starting date : 01-10-2016

Contact :

Rafael A. Garcia

CEA - DSM/IRFU/SAp/LDEE

0169082725

Thesis supervisor :

Rafael A. Garcia

CEA - DSM/IRFU/SAp/LDEE

0169082725

More : http://irfu.cea.fr/Sap/LDEE/LDEE_web/index.html

Red giants proved as an incredible source of information for testing theoretical models of stellar structure and evolution (e.g. Bedding , ... García et al. , 2011, Nature). Asteroseismology allows us to determine stellar masses and radius very simply by measuring the global properties of the oscillation modes, and through the application of seismic scaling relations from the solar values (Kjeldsen & Bedding 1995). However, these scaling relations have never been properly calibrated despite their widespread application in the analysis of CoRoT and Kepler data. On the other hand, eclipsing binary stars have long been considered a valuable tool for astrophysics, as the photometric and spectrometric observations allows us to determine the mass and radius of each component of the system, without requiring any prior knowledge of the distance to the star of or the stellar type (e.g. Gaulme et al. 2014 ApJ). The objective of this thesis is to combine the photometric and spectrometric analysis of eclipsing binary systems with the seismic analysis of at least one of the components of such multiple systems in order to independently calibrate the seismic scaling relations. This improvement will be a major asset for a more precise characterization of any field star showing pulsations. In particular, the exoplanetary systems and so the mass and size of planets already discovered by the transit method in missions like CoRoT, Kepler and K2. Finally, the methods derived in this thesis will be extremely useful to better characterise the stars observed by the future M3 ESA mission PLATO.



Along this thesis, the student will learn the different techniques of seismic analysis (Bayesian methods, Maximum likelihood fittings , etc) and will become familiar with different types of observations (e.g. photometry, spectroscopy, …). In a second phase, the student will take in hand the stellar evolution code (e.g. MESA or STAREVOL) to do the best modeling of these systems. At the end of the PhD the student will have used all the stages of the seismic analyses, he will better calibrate the seismic scaling relations and hence he will be in the best position to analyze the forthcoming data provided by the American satellite TESS that will be launch around 2018.

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