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 Résumés

Remarque : les enregistrements des séminaires sont disponibles sur seminars.lam.fr.



6 March 2020 - 11h

  • Grégoire Danger (Associate Professor - AMU)
  • From Astrochemistry to Planetary Chemistry. An Astrobiological Point of View

Complex organic molecules are detected in gaseous and solid phases of astrophysical objects. The origin of these molecules is still debated, but a large part is supposed to form on the surface of frozen grains. These icy grains observable in dense molecular clouds will be altered by highly energetic processes (VUV photons, ions, electrons) during the formation of planetary systems. These alterations allow the activation of molecules initially present in these ices, resulting in the development of a significant
chemical reactivity. In certain environments such as the solar nebula, these grains can be heated, releasing in the gas phase a large part of the complex organic molecules initially formed on the surface or within the ice bulk. Some of these molecules can also react inside the ice forming nonvolatile molecules that remain on the grains leading to the formation of refractory organic residues. Part of the transformed grains can then accrete, resulting in interplanetary objects such as comets or asteroids. As a result, some of the organic matter present in solar system objects could come from ices found in dense molecular clouds. A part of this material can then be delivered at the surface of telluric planets as observed on Earth through the analysis of meteorites. The question of the role played by this exogenous
organic matter in the emergence of a prebiotic chemistry in planetary environments is then a key issue in astrobiology.
Based on laboratory experiments, we develop analytical strategies to study the chemistry generated by the processing of such ices. We particularly demonstrate the richness of molecules formed. We also investigate the impact of the initial composition of the ice on the abundance of molecules observed in the gas phase as well as on the molecular composition of the remaining residues after the desorption of the most volatile compounds. Furthermore, our analyses show that this ice chemistry leads to the formation of all building blocks needed to start a prebiotic chemistry on telluric planets. We further develop new experiment to investigate the evolution of such matter in the conditions of the primitive Earth.
All results obtained from our experiments suggest that ices of astrophysical objects are key environments to generate a rich molecular diversity and question its potential role in the emergence of a prebiotic chemistry on primitive Earth environments.

14 February 2020 - 11h

  • Elise Vernet (ESO)
  • Design and performance of the ESO ELT adaptive and fast steering mirrors

The optical design of the ELT is based on a novel five-mirror scheme capable of collecting and focusing the light from astronomical sources and feeding state-of-the-art instruments for the purposes of imaging and spectroscopy. Thanks to the combined use of M4 and M5, the optical system is capable of correcting for atmospheric turbulence and the vibration of the telescope structure itself induced by motion and wind.

The presentation will focus on the technological specificities and performance of the two mirrors. The adaptive mirror is using the well-developed adaptive secondary technology but the M4 design has been tuned to reduce risks during the manufacturing and fulfil the ELT needs. In the first part, the technological changes of M4 will be highlighted and the implications discussed. The second part of the talk will be dedicated to M5.
The fast steering mirror is a ultra-light and stiff mirror mounted on a stiff tip tilt stage. After presenting the fast steering requirements and the associated flow down on the two subsystems, I will focus on the mirror design and the criticalities of manufacturing a 2.5 meter class Silicon Carbide mirror for observations at visible wavelengths.

31 January 2020 - 11h

  • Gaitee Hussain (ESO)
  • The evolution of magnetic activity in solar-type stars

Solar-type stars display signs of magnetic activity at all wavelengths, from energetic X-ray and UV flares to photometric variability caused by the presence of large cool spots. The magnetic activity in solar-type stars evolves as they age, affecting the environment in which planets themselves form and evolve. Over the past two decades Doppler imaging techniques have allowed us to detect and map the surface magnetic fields of solar-type stars over a wide range of evolutionary states. In this talk I will explain how we derive and interpret magnetic field maps of solar-type stars and review what they have taught us about the evolution of magnetic activity from the PMS stage through to our own Sun.

17 January 2020 - 11h

  • Stephane Basa & Laurent Martin (LAM)
  • THESEUS

The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a mission concept developed in the last years by a large European consortium and currently under study by the European Space Agency (ESA) as one of the three candidates for nextM5 mission (launch in 2032). THESEUS aims at exploiting high-redshift GRBs for getting unique clues to the early Universe and, being an unprecedentedly powerful machine for the detection, accurate location (down to∼arcsec) and redshift determination of all types of GRBs (long, short, high-z, under-luminous, ultra-long) and many other classes of transient sources and phenomena, at providing a substantial contribution to multi-messenger time-domain astrophysics. Under these respects, THESEUS will show a strong synergy with the large observing facilities of the future, like E-ELT, TMT, SKA, CTA, ATHENA, in the electromagnetic domain, as well as with next-generation gravitational-waves and neutrino detectors, thus greatly enhancing their scientific return.
LAM is involved in the development of one of the 3 on-board instruments : the IRT for Infra-Red Telescope. The participation of the LAM consists in the supply of the structure of the instrument as well as the mirrors. The Instrument Scientist, the Optical Architect and the Mechanical Architect are among the key persons of the Project. The LAM is also responsible for the assembly and all of the tests that will take place in Marseille.
The presentation will be in French with slides in English.

10 January 2020 - 11h

  • Astrid Lamberts (OCA)
  • Gravitational wave progenitors near and far

Gravitational waves (GW) have opened a new window on our universe, providing us unique information on fundamental physics, stellar evolution, high energy astrophysics and global star formation in the universe. As the first catalog of GW events observed by LIGO/Virgo has become available, the main question is "where do black hole mergers come from ?" In this talk I will detail in which types of environments progenitors stars of GW events typically form and how the properties of GW events can inform on binary evolution. I will first focus on the mass black holes observed by LIGO/Virgo before presenting predictions for space-based GW detector LISA. LISA will be a detector operating at lower frequencies and will be sensitive to stellar compact binaries in the Milky Way, such as white dwarfs or black holes.

20 December 2019 - 11h

  • Florence Durret (IAP and Sorbonne Universite)
  • Galaxy clusters and their environment

Clusters of galaxies are located at the intersection of cosmic filaments. I will first describe how we have found large extensions around clusters, at optical and/or X-ray wavelengths, suggesting that we are indeed detecting the cosmic web around clusters, and I will discuss some galaxy properties in one of these extended filaments.

At the cluster scale, I will then describe our searches for substructures in X-rays and show how X-ray temperature, pressure, entropy and metallicity maps can give informations on the cluster history by comparing them with hydrodynamical simulations.

Finally, I will talk about several properties of galaxies in clusters, such as galaxy luminosity functions, brightest cluster galaxies, jellyfish galaxies, and asymmetric galaxies.

13 December 2019 - 11h

  • Elsa Huby (LESIA)
  • Spectroscopy below the diffraction limit with the FIRST pupil remapper at the Subaru Telescope

FIRST (Fibered Imager foR a Single Telescope instrument) is a post-AO instrument that enables high contrast imaging and spectroscopy at spatial scales below the diffraction limit. FIRST achieves sensitivity and accuracy by a unique combination of sparse aperture masking, spatial filtering by single-mode fibers and cross-dispersion in the visible. Currently integrated as a module of the Subaru Coronagraphic Extreme AO system (SCExAO), on-sky commissioning data show the detection of several stellar companions, and in particular of the Alpha Equu binary system angularly separated by 0.6 λ/D (11mas). Even at such a separation, FIRST delivers information on the companion spectrum, providing valuable constraints on the stellar parameters of the system such as the effective temperatures and surface gravity. On-going developments based on photonics technology focus on improving the instrument’s stability and sensitivity, and hence increasing the dynamic range. By coupling high angular resolution and spectral resolution in the visible, FIRST offers unique capabilities in the context of the detection and spectral characterization of close companions, especially on the future 30m-class telescopes.

29 November 2019 - 11h

  • Mélanie Heil (ESA)
  • ESA’s Enhanced Space Weather Monitoring System

ESA’s Space Situational Awareness Programme aims at protecting space and ground assets against adverse effects from space. The Space Weather Segment is focussing on such effects due to the activity of our Sun.

Monitoring of the Earth’s and Sun’s environment is an essential task for the now- and forecasting of Space Weather and the modelling of interactions between the Sun and the Earth. Due to the asymmetry and complexity of Earth’s magnetosphere, the involved particle environment and its dynamics, it is necessary to capture the state of the magnetic field and the particle distribution in a sufficiently large number of sampling points around the Earth, such that it allows state-monitoring and modelling of the involved processes with sufficient accuracy and timeliness.

ESA is implementing an enhanced space weather monitoring system, which includes the Lagrange mission to observe solar activity from the 5th Lagrange point of the Sun-Earth system and the establishment of a Distributed Space Weather Sensor System (D3S) to observe the effects of solar activity within Earth’s vicinity. Space weather instrumentation traditionally is highly miniaturised, and therefore appears to be well suited for small satellite systems, which could become competitive to the usually followed hosted payload approach while allowing for more flexibility with respect to the flown payload and orbital requirements.

I will present the current status and future plans of ESA’s Space Weather activities particularly focussing on D3S.

22 November 2019 - 11h

  • Françoise Combes (IRAP)
  • Molecular tori, black hole fueling, and feedback in nearby AGN

Recent molecular line observations with ALMA in several nearby Seyferts have revealed the existence of molecular tori, and the nature of gas flows at 10-20pc scale. At 100pc scale or kpc-scale, previous work on gravitational torques had shown that only about one-third of Seyfert galaxies experienced molecular inflow and central fueling, while in most cases the gas was stalled in rings. At higher resolution, i.e. 10-20pc scale, it is possible now to see in some cases AGN fueling due to nuclear trailing spirals, influenced by the black hole (BH) potential. This brings smoking-gun evidence for nuclear fueling. In our sample galaxies, the angular resolution of up to 80mas allows us to reach the BH-zone of influence and the BH mass can be derived more directly than with the M-sigma relation.

15 November 2019 - 11h

  • Pier Stefano Corasaniti (LUTH)
  • Galaxy Cluster Cosmology Beyond Cluster Number Counts

In the past years, dedicated survey programs have provided increasingly large samples of galaxy cluster observations which have opened the way to probing cosmology with galaxy clusters. These carry a wealth of cosmological information encoded in the cluster abundance, spatial clustering and density profile. To date cosmological constraints have been mainly inferred from cluster number count measurements. In this talk I will review recent results and motivate the use of complementary galaxy cluster observables. In particular, I will discuss the use of cluster sparsity measurements as a novel cosmological probe.

8 November 2019 - 11h

  • Pascal Tremblin (CEA Saclay)
  • Thermo-compositional diabatic convection in the atmospheres of brown dwarfs, exoplanets, and in Earth’s atmosphere and oceans

By generalizing the theory of convection to any type of thermal and compositional source terms (diabatic processes), we show that thermohaline convection in Earth’s oceans, fingering convection in stellar atmospheres, and moist convection in Earth’s atmosphere are derived from the same general diabatic convective instability. We also show that "radiative convection" triggered by the CO/CH4 transition with radiative transfer in the atmospheres of brown dwarfs is analogous to moist and thermohaline convection. We derive a generalization of the mixing-length theory to include the effect of source terms in 1D codes. We show that CO/CH4 "radiative" convection could significantly reduce the temperature gradient in the atmospheres of brown dwarfs similarly to moist convection in Earth’s atmosphere, thus possibly explaining the reddening in brown dwarf spectra. By using idealized 2D hydrodynamic simulations in the Ledoux unstable regime, we show that compositional source terms can indeed provoke a reduction of the temperature gradient. The L/T transition could be explained by a bifurcation between the adiabatic and diabatic convective transports and seen as a giant cooling crisis : an analog of the boiling crisis in liquid/steam-water convective flows.

The study of the impact of different parameters (effective temperature, compositional changes) on CO/CH4 radiative convection and the analogy with Earth moist and thermohaline convection is opening the possibility of using brown dwarfs to better understand some aspects of the physics at play in the climate of our own planet.

This mechanism, with other chemical transitions, could be present in many giant and Earth-like exoplanets. We present first results towards the simulation of this process for the CO/CO2 transition in secondary atmospheres of hot rocky exoplanets (young or irradiated) which could be applied to the primitive stages of the atmospheres of Earth, Mars or Venus.

18 October 2019 - 11h

  • Frédéric GALLIANO (AIM, CEA/Saclay, France)
  • Dust Evolution from the Perspective of Nearby Galaxies

A precise characterization of the grain properties is crucial for understanding the life cycle of the interstellar medium (ISM) and the evolution of galaxies. Nowadays, most of our knowledge of dust physics comes from studies of the Milky Way (MW). However, an increasing number of results on nearby galaxies provide unique discriminating constraints on fundamental grain processes. Indeed, nearby galaxies harbor a wider diversity of environmental conditions (metallicity, star-formation activity, etc.) than can be found in the MW. In particular, these nearby systems allow us to observe dust in extreme conditions, providing us valuable empirical information on grain evolution. They also constitute a necessary intermediate step toward understanding distant galaxies, as they are spatially resolved and have better wavelength coverage.

I will start with a general introduction, presenting the challenges in dust physics, and the recent advances in our understanding of the grain properties of the nearby Universe. I will then review several studies of the DustPedia project. This european collaboration aims to build a reference survey of ≈900 nearby, NIR-selected galaxies, observed with Herschel. I will detail the effort in modelling techniques we have carried out to provide the most accurate analysis possible of our data. I will finally present the various scaling relations and dust evolution trends derived among and within galaxies. I will discuss, in particular, the evolution of the dust-to-gas mass ratio and the fraction of aromatic feature carriers as a function of metallicity and star formation activity.

4 October 2019 - 11h

  • Jean-Luc Beuzit (LAM)
  • SPHERE, five years at the VLT

SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research in Europe) is a second-generation instrument for the ESO Very Large Telescope, dedicated to the direct detection and spectral characterization of giant extra-solar planets. SPHERE combines an extreme adaptive optics system, various coronagraphic devices and a suite of focal instruments providing imaging, integral field spectroscopy and polarimetry capabilities in the visible and near-infrared spectral ranges. The instrument has now been in operation for 5 years and has produced a harvest of leading scientific results. I will give an overview of the instrument, highlight the human adventure behind its development, review its performance and present a selection of the major results.

6 September 2019 - 11h

  • Annie Hughes (IRAP)
  • PHANGS : Star formation, feedback and chemical enrichment in nearby galaxies

The Physics at High Angular resolution in Nearby Galaxies (PHANGS) project is pursuing thee major observing programmes with ALMA, VLT/MUSE and the HST in order to study the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution across a representative sample of star-forming main sequence galaxies in the local Universe (d<20Mpc). With observations at high angular resolution (<100pc), the PHANGS legacy datasets provide a detailed, panchromatic view of ionised gas, stellar light, and the cold molecular gas in nearby galaxies and enable statistical studies of star formation, feedback, and chemical enrichment across different galaxy environments. In this talk, I will give an overview of the PHANGS project, and highlight our latest results for the physical conditions in the molecular gas reservoir, the star formation activity and chemical enrichment in PHANGS galaxies.

28 June 2019 - 11h

  • Peter Capak (Caltech)
  • Developing a Standard Model of Galaxies

The Physics at High Angular resolution in Nearby Galaxies (PHANGS) project is pursuing thee major observing programmes with ALMA, VLT/MUSE and the HST in order to study the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution across a representative sample of star-forming main sequence galaxies in the local Universe (d<20Mpc). With observations at high angular resolution (<100pc), the PHANGS legacy datasets provide a detailed, panchromatic view of ionised gas, stellar light, and the cold molecular gas in nearby galaxies and enable statistical studies of star formation, feedback, and chemical enrichment across different galaxy environments. In this talk, I will give an overview of the PHANGS project, and highlight our latest results for the physical conditions in the molecular gas reservoir, the star formation activity and chemical enrichment in PHANGS galaxies.
In this presentation Peter Capak will argue that a combination of large galaxy surveys and the latest machine learning techniques are allowing astrophysicists to develop a robust statistical model of the extra-galactic universe. If optimally constructed, this model would encapsulate all available information on the likelihood of observing a given type of galaxy as well as its distribution in space and cosmic epoch. The initial motivation for developing elements of this model was improved constraints on dark energy and dark matter, but it also contains significant information on how galaxies form and evolve. He will show how early version of this model have significantly improved photometric redshifts for weak lensing and can be used for spectroscopic target selection. He will conclude with examples of how he is using his models to optimally design observation with facilities in high demand such as Keck, ALMA, and the future JWST and what future techniques need to be developed.

21 June 2019 - 11h

  • Hendrik Hildebrandt (Alfa-Bonn)
  • Cosmological Weak Gravitational Lensing

Gravitational lensing represents a unique tool to study the dark Universe. Small distortions in the images of galaxies caused by the gravitational lensing effect of the matter distribution in the Universe can be detected over the whole sky. Measuring these coherent distortions makes dark matter structures "visible", allows us to study their growth over cosmic time, and yields cosmological insights complementary to other probes like the cosmic microwave background (CMB). Ongoing wide-field imaging surveys exploit this weak gravitational lensing technique to come up with competitive constraints on important cosmological parameters and insights on fundamental physics.

In this talk I will first introduce the basic concepts of weak gravitational lensing, review the history and challenges of weak lensing measurements, and then concentrate on recent results from the ongoing European Kilo Degree Survey (KiDS) and VISTA Kilo-degree Infrared Galaxy Public Survey (VIKING) projects. These KiDS/VIKING measurements show some tension with CMB measurements from the Planck mission when the standard cosmological model is assumed. The results will be put into context and compared to findings from the two other big cosmic shear experiments (HSC and DES). I will also present brand-new results from a Self-Organised-Map-based calibration of the KiDS+VIKING redshifts and how this influences the cosmological conclusions. Through a careful re-assessment of the HSC and DES results I will show that the discrepancies in large-scale-structure parameters we are seeing today are approaching a level of significance that is similar to the tension in the Hubble constant. Taken together this might hint at a serious problem of the standard ΛCDM paradigm in simultaneously explaining early- and late-time cosmic structure formation. I will conclude with an outlook towards the big experiments of the next decade in this field of research, Euclid and the Large Synoptic Survey Telescope that have the potential to yield some definitive answers to these questions.

14 June 2019 - 11h

  • Vianney Lebouteiller (Laboratoire AIM - CEA Saclay)
  • The interstellar medium of nearby primitive galaxies

The lack of detection of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. In particular, CO, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments. A potentially large fraction of H2 is thus expected to reside in the so-called CO-free gas, where it could be traced by neutral gas observed with infrared cooling lines



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