Elbereth conference 2020

26 févr. 2020, 09:00 → 28 févr. 2020, 23:00 Europe/Paris

Amphithéatre (Institut d’Astrophysique de Paris)

Welcome to the Indico page of the Elbereth conference 2020!

Every year, the Elbereth conference gathers PhD students from various astronomy and astrophysics laboratories of Île-de-France. Organized by PhD students and for PhD students, it aims to develop links between students and allows the participants to discover the most recent works in astrophysics.

You are invited to submit an abstract for a 15-minute oral presentation (subject to acceptance).

Before submitting an abstract, do not forget to register here at the conference.

You need to log into indico to be able to submit an abstract. If you do not have an account, you can create one or log in with your institutionnal account (Edugain Single Sign On)

 

mercredi 26 février

09:30 → 09:45 Welcome speech

Orateurs: Aurélien Stcherbinine (IAS / LATMOS), Deborah Bardet (Laboratoire de Météorologie Dynamique), Nicolas DAGONEAU (CEA/Saclay - IRFU/DAp/LISIS), Océane Barraud (LESIA, Observatoire de Paris-PSL), kevin barjot (LESIA)

Elbereth_2020_Opening_presentation.pdf

09:45 → 10:15 Invited talk: Micaela Oertel

09:45 Micaela Oertel

After a PhD thesis in Darmstadt (Germany) and stays in Lyon and at CEA Bruyères-le-Châtel, Micaela Oertel joined the Laboratoire Univers et Théories (LUTH) in Meudon in 2005. Her research interests in nuclear astrophysics concern neutron stars, binary neutron star mergers and core-collapse supernovae. These objects are not only at the origin of some of the most energetic events in the Universe and excellent sources of gravitational waves, but comprise matter at extremes of density, temperature and composition, too, challenging our understanding of fundamental interactions.

Orateur: Micaela Oertel (LUTH)

10:15 → 10:45 Coffee break

10:45 → 11:30 Talk

10:45 The LMD general circulation models: tools for a better understanding of atmospheric planetary physics

THE LMD GENERAL CIRCULATION MODELS : TOOLS FOR A BETTER
UNDERSTANDING OF ATMOSPHERIC PLANETARY PHYSICS. *A. Bierjon 1 , A. Delavois 1 , T. Pierron 1 , D. Bardet 1 , J. Naar 1 , A. Boissinot 1 , F. Forget 1 , E. Millour 1 , A. Spiga 1 , F. Hourdin 1 , T.Dubos 1 .
1 Laboratoire de Météorologie Dynamique, UMR CNRS 8539, Institut Pierre-Simon Laplace,
Sorbonne Universités, UPMC Univ Paris 06, 4 place Jussieu, 75005, Paris, France.

Introduction

General Circulation Models have proven to be relevant tools to study the atmospheric features of planetary bodies in our universe. Therefore, at the Laboratoire de Météorologie Dynamique, they are developped and used since the 1990s [1] to supply the research with plenty of numerical simulation data to analyze, leading to a lot of results and publications.
Gathering the knowledge we have on the climate processes that occur on the variety of celestial bodies, these models are nowadays the common means to study the atmospheric global trends on bodies like the Earth, Venus, Mars, Jupiter, Saturn, Titan, Pluto, but also exo-planets for recent or paleo-climates.
In this presentation, we introduce the general characteristics of the LMD GCMs that are used byour PhD students and colleagues, in such a way as to share knowledge with the audience about these useful tools.

Theoretical bases and hypotheses

Every GCMs come from the application of the fundamental equations of fluid dynamics, a.k.a. the Navier-Stokes equations, to a rotating sphere. By constraining the problem to this specific case, and via some hypotheses based on the characteristic scales of a planetary flow, one can derive these Navier-Stokes equations into the meteorology primitive equations, which can be used to describe the general atmospheric circulation around a planetary body.

The dynamical grid

On the dynamical grid, GCMs resolve the general or large-scale 3D circulation and ensure the horizontal transport from adjacent cells. This dynamical core can be applied to all GCMs, since it is generic enough to represent any planet’s general circulation.
Still, there is a variety of dynamical cores around the world, and two are actually in use at LMD : LMDZ, the historical longitude-latitude grid, and DYNAMICO [2], a more recent icosahedral high-resolution grid, dedicated to massively parallel computation.

Physics representation

Coupled with the dynamical grid, the second part consists in the juxtaposition of independent vertical 1D columns, in which the physical parametrizations and subgrid-scale processes are computed. This physical part is specific to each planet and to the particular interactions that exist on the body we study – non-exhaustively : radiative transfer, chemistry, gravity waves, boundary layer, surface-atmosphere interactions, cloud microphysics, aerosols,...

References
[1] Hourdin, F. (1992). A new representation of the CO2 15 μm band for a Martian general circulation model. J. Geophys. Res., 97(E11) :18,319–18,335.
[2] Dubos, T., Dubey, S., Tort, M., Mittal, R., Meurdesoif, Y., and Hourdin, F. (2015). DYNAMICO-1.0, an icosahedral hydrostatic dynamical core designed for consistency and versatility. Geoscientific Model Development 8, 3131-3150.

Orateurs: Antoine Bierjon (LMD), Antony Delavois (LMD), Thomas Pierron (LMD)

diapo_Bierjon_Delavois_Pierron.pdf

11:00 Global climate modelling of Saturn's stratospheric equatorial oscillation

The Composite InfraRed Spectrometer (CIRS) on board Cassini revealed an equatorial oscillation of stratospheric temperature, reminiscent of the Earth’s Quasi-Biennial Oscillation (QBO), as well as anomalously high temperatures under Saturn’s rings. To better understand these predominant features of Saturn’s atmospheric circulation in the stratosphere, we have extended towards higher altitudes the DYNAMICO-Saturn global climate model (GCM), already used in a previous publication to study the tropospheric dynamics, jets formation and planetary-scale waves activity. Firstly, we study the higher model top impact on the tropospheric zonal jets and kinetic energy distribution. Raising the model top prevents energy and enstrophy accumulation at tropopause levels.
The reference GCM simulation with 1/2$^{\circ}$ latitude/longitude resolution
and a raised model top exhibits a QBO-like oscillation produced by resolved planetary-scale waves. However, the period is more irregular and the downward propagation faster than observations. Furthermore, compared to the CIRS observation retrievals, the modeled QBO-like oscillation underestimates by half both the amplitude of temperature anomalies at the equator and the vertical characteristic length of this equatorial oscillation. This QBO-like oscillation is mainly driven by westward-propagating waves; a significant lack of eastward wave-forcing explains a fluctuating eastward phase of the QBO-like oscillation. At 20$^{\circ}$N and 20$^{\circ}$S latitudes, the DYNAMICO-Saturn GCM exhibits several strong seasonal eastward jets, alternatively in the northern and southern hemisphere. These jets are correlated with the rings' shadowing. Using a GCM simulation without rings' shadowing, we show its impact on Saturn's stratospheric dynamics. Both residual-mean circulation and eddy forcing are impacted by rings' shadowing. In particular, the QBO-like oscillation is weakened by an increased drag caused by those two changes associated with rings' shadowing.

Orateur: Deborah Bardet (LMD)

2020-02-26_DBARDET_Elbereth.pdf

11:15 Water ice cycle during recent martian paleoclimates

Introduction: Corroborating evidences in geomorphology and modeling has unveiled the presence of a subsurface latitude-dependent mantle (LDM) of water-ice-rich deposits down to 30° latitude in both martian hemispheres [1]. These layers appear to be less than ~ 2Myr and were possibly deposited as snowfall in response to climate change driven by shift in obliquity, similar to Earth glacial/interglacial periods [2].
However, martian climate models usually struggle to reproduce environmental conditions required to form LDM under recent paleoclimatic orbital forcing.
We present a new parametrization of ice/frost albedo which, along with radiatively active water-ice clouds (RAC), predicts ice accumulation rates in mid-latitudes compatible with deposition of a tens of meters-thick LDM under recent obliquities (several incursions to 35°).

Evolution of water stability regions with obliquity: Remnant glacial and periglacial geological features are observed at equatorial and mid-latitudes on Mars, a few tens of million years old. These landforms likely result from equatorward shift of water-ice stability with rising obliquity [3]. This tropical ice becomes unstable during low obliquity phases, and ice has been modeled to accumulates in high latitudes [4,5]. Yet, these former ice reservoirs are millions of years older than the LDM, likely formed during higher obliquity phases (~45°). The water source of the LDM is therefore not thought to be of low-latitude origin, but may be remobilized polar water-ice.

Water-ice clouds in recent paleoclimates: Water-ice clouds effects have a small effect on the present-day martian climate [6], corresponding to a ~25.2° obliquity. When obliquity shifts up to 35°, atmospheric humidity is enhanced by polar warming and water-ice cloud become a key element of martian climate [7,8].
Their radiative effect strongly warms the atmosphere, amplifies meridional circulation and water transport toward tropical latitudes. [7] showed that taking into account radiatively active clouds allow for mid-latitude ice deposits considering only polar caps as a water source in this obliquity regime. However, the accumulation of these ice deposits required the prescription of high atmospheric dust content to ensure its persistence during summer.
Frost and ice albedo: During recent high obliquity episodes up to ~35°, ice accumulates in mid-latitudes as frost. Frost should have a much higher albedo than perennial ice [9]. This was not taken into account in [7]. We improve the parametrization of ice albedo by decoupling older ice,with a canonical albedo of 0.35, and frost, whose albedo can reach 0.7. We find that it has a compelling influence regarding surface water stability and persistence over the years. High albedo inhibits sublimation in summer by lowering surface heating.

Paleoclimatic simulations: Using this refined parametrization, we perform climatic simulations at 35° obliquity with null eccentricity. The corresponding accumulation rates of ice are compatible with the setting of hundreds of meters of LDM down to ~45° latitude in both hemispheres and its persistence year by year (Figure 1). In the last ~2 Myr on Mars, obliquity has reached ~35° a dozen times, for approximately 1000 years each time [10]. Assuming an efficient preservation process, the accumulation rate is sufficient to form a hundreds of meters thick latitude-dependent mantle of ice-rich deposits. The latitudinal extension of the LDM down to 30° isn’t represented in these simulations, but many orbital configurations remain to be explored with our model.

Future studies: These preliminary results are part of the “Mars Through Time” program. Scientific perspectives include understanding the formation of LDM, and more generally investigating recent paleoenvironments leading to the formation of geologically young glacial and periglacial landforms on Mars.

Orateur: Joseph Naar (Laboratoire de Météorologie Dynamique)

elbereth_martian_paleoclimates_naar.pdf

11:30 → 12:00 Invited talk: Star's Up 2

11:30 Star's Up 2

50 ans après les premiers pas de l’Homme de sur la Lune, continuons à faire rêver et sensibilisons l’auditoire aux enjeux de la recherche spatiale. Nous avons lancé STAR’sUP en 2019 convaincus qu’un festival exigeant, mais résolument grand public et créatif est un outil fédérateur. STAR’s UP est le festival où se rencontrent les spécialistes – tant publics que privés - des sciences de l’espace et le grand public. Il participe au décloisonnement des savoirs et des spécialités dans l’esprit d’un cluster éphémère.

Le festival est organisé par l’association Meudon Space Contrator avec le soutien de l’association La Bêta-Pi sur le volet médiation scientifique. Nos deux associations basées à Meudon ont pour ambition de faire vivre la culture scientifique et technique au plus grand nombre.

Orateur: Julien Rol Malherbe (La Bêta-Pi)

12:00 → 13:30 Lunch break

13:30 → 14:15 Talk

13:30 Molecular gas and star formation in the CARLA J1103+3449 cluster at z~1.4

Galaxy evolution from a star-forming active galaxy rich in gas, dust, and young blue stars to a passive, ‘dead’ galaxy, void of gas and filled with an old population of red stars depends mainly on the molecular gas reservoirs present inside a galaxy. Molecular gas plays an important role since it acts as a star formation fuel. Detecting and estimating the molecular gas content inside a galaxy indicates that this galaxy is probably still star-forming.
In this project, I worked with my supervisor and collaborators on the IRAM NOEMA observations of a spectroscopically confirmed CARLA J1103+3449 cluster at z ∼ 1.44. We measure the molecular gas content of confirmed cluster members and compare it with observations in other clusters and in the field at similar redshifts (Markov et al. to be submitted). The work on this project includes data reduction, imaging and analysis of NOEMA observations using gildas software. We target a CO(2-1) emission line redshifted at ν =94.5GHz, inside the central region of the cluster. We detect an extended continuum emission centered on the RLAGN with two components with a SNR ∼ 26σ and SNR ∼ 6σ. These two components originate from a synchrotron emission of a supermassive black hole in the cluster center and are roughly tracing the two radio jets from the work of Best et al. (1999). We detect a CO(2-1) emission in the central cluster region, we extract the spectra and derive the velocity integrated flux. We estimate a substantial amount of molecular gas of $M_{gas} = 1.7×10^{11} M_⊙$ extended around the central RLAGN. We kinematically resolve the two components with a SNR ∼ 3σ and SNR ∼ 4.5σ. Both components are blueshifted with respect to the RLAGN and are spatially separated from the RLAGN by ∼ 15 kpc. We discuss several hypotheses to explain these molecular gas reservoirs. We argue that the bipolar radio emission favors the outflow/inflow hypothesis, i.e. the two components are either originating from cold gas that is lifted ∼ tens of kpc away from the RLAGN by the two jets, or it condensed from an interaction of the AGN jets with intracluster medium (ICM) and it has not settled yet on the RLAGN.

For the RLAGN and other cluster members we use 3σ values of the rms noise to estimate upper limits of molecular gas masses. Furthermore, we use the stellar mass estimates from Amodeo et al. (in prep.), to compute galaxy parameters and compare them with parameters of similar galaxies in other clusters and the field galaxies from the PHIBSS survey in order to understand the stage of the evolution of our galaxies.

Orateur: Vladan Markov (PhD student)

Markov_Elbereth.pdf

13:45 The necessity of a large-scale turbulent driving to regulate star formation in massive galaxies

The Schmidt-Kennicutt law links the star formation rate (SFR) of a galaxy or its subregions to the contained amount of gas, and remains true for a wide range of galaxies and redshifts. Understanding its origin is crucial to improve our knowledge of the star formation process. One main question is to determine which are the processes responsible of the regulation of the star formation rate, which would be much higher if only the self-gravity of the gas was at play.

In this talk I will present the results of simulations of a kiloparsec cube section of massive galaxies featuring different kinds of feedbacks, such as the formation of HII regions, the explosion of supernovae, and the emission of UV. We will see that such feedbacks are not sufficient to quench star formation to the level of the observed rates but that an additional injection of turbulent energy from large scale structure is able to reduce the SFR to a more reasonable level.

Orateur: Noé Brucy (CEA Saclay - AIM)

BrucyElbereth2020.pdf

14:00 A super resolution method applied to WISDOM martian radar soundings

The rover of the ExoMars 2020 mission will be the first able to collect samples down to 2m in the Martian subsurface. To select the best drilling sites available in terms of mission safety and scientific interest, the ExoMars science team will have at their disposal the soundings of the WISDOM ground penetrating radar. The vertical resolution of those soundings is limited by the bandwidth of the instrument. To enhance this resolution, the Bandwidth Extrapolation technique is employed. It allows the extrapolation of a certain amount of frequencies which are not in the spectra measured by the radar. The parameters required by the method were determined with experimental WISDOM soundings from different field campaigns, and the resolution improvement as well as the conservation of amplitude ratios was confirmed on experimental soundings from semi-controlled environments. In 2021, WISDOM will be able to collect soundings with a vertical resolution 2 to 3 times better than expected with the instrument bandwidth.

Orateur: Nicolas Oudart (LATMOS)

WISDOM_Elbereth_Nicolas_Oudart_02_2020.pdf

14:15 → 14:45 Invited talk: Caroline Freissinet

14:45 → 15:15 Coffee break

15:15 → 16:15 Talk

15:15 Characterizing Galaxy Protoclusters: a case study of a Planck-selected candidate

Understanding how and when galactic structures formed is a major unsolved problem in Astrophysics, yet such sources are also very red and faint, making their confirmation a challenge. Nascent galaxy overdense regions or "protoclusters" are relatively brighter at z=2-4, during which the in-situ star formation rates and/or AGN activities peaked. While obtaining spectroscopic confirmation of multiple member galaxies can be slow-going, at the same time there is ample useful photometric information. We present a study of the protocluster candidate PLCK G256.8-33.2, which is drawn from the Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey. SPHerIC identified 82 galaxy protocluster candidates at z=1.3-3.0 using mid- through far-infrared imaging data. In this preliminary analysis we include also optical and near-infrared imaging to do the matched photometry and fit Spectral Energy Distribution (SEDs) to the galaxies in to measure their photometric redshifts.

Orateur: Thibaut Perdereau

Perdereau_Thibaut_ELBERETH_2020.pdf

15:30 Bayesian tools to unveil the properties of galaxies

The emission lines arising from galaxies are commonly used as proxies to probe the physical and chemical state of galaxies. Spectra observed in the optical domain using ground base telescopes (ALMA, VLT) and in the infrared domain (Herschel, Spitzer, and the coming missions JWST, SPICA) provide unique “finger-prints” of the interstellar medium, in which are embedded a large set of information concerning the stellar, gas and dust content of the observed galaxy. Such emission can be mapped at local scales (kpc) in the closest galaxies in our neighborhood (z~0) but observations at higher red-shifts are most of the time integrated fluxes emerging from the whole galaxy. The interpretation of such spectra is far from being straight forward, especially because multiple components within the galaxy contribute to the observed emission. If most of the light we see originates from the stars and the ionized gas that surrounds them, there is also a non-negligible emission from dust, neutral or partly ionized gas and molecular clouds. To understand what those spectra reveal, there is a critical need to provide reliable multi-phase modeling of the interstellar medium of galaxies and develop statistical tools to analyze them. In this talk I will present Cloudy, the photo-ionization and photo-dissociation code I used to model galaxies, and how its use can be refined by combining models to realistically mimic the patchy, non-homogeneous nature of the interstellar medium. Using a simple grid of models, I will present a strategy to extract galactic properties from the emission lines available using Bayesian methods. Such a tool could be of great interest to analyze spectra but also to serve as a prediction tool in the framework of spatial missions such as SPICA (ESA pre-selected mission).

Orateur: Lise RAMAMBASON (CEA/AIM)

Bayesian tools to unveil the properties of low-metallicity galaxies.pdf

15:45 The Cepheid Leavitt law from Gaia DR2 parallaxes of resolved companions

Cepheids represent a fundamental tool for measuring the distances in the Universe thanks to the Leavitt law (period-luminosity) relation. In order to calibrate this relation accurately, precise distance measurements are required. The Gaia satellite monitors a large number of Galactic Cepheids, and will eventually provide extremely accurate parallaxes to hundreds of them. This will considerably improve the calibration of the Leavitt law, setting it on a solid basis of trigonometric distance measurements.

However, the second Gaia data release (DR2) shows that variable star parallaxes are subject to biases due to saturation (for the nearest stars) and to the large amplitude of their color variation. As a result, the calibration of the Leavitt law using the present DR2 Cepheid parallaxes is unreliable. In order to overcome this difficulty, we used the parallaxes of the detached companions of a sample of 23 Galactic Cepheids as a proxy for the parallaxes of the Cepheids themselves. Their Gaia parallaxes are unaffected by saturation and color related biases, since they are relatively faint and stable stars. Based on these parallaxes, we obtained a new calibration of the Galactic Leavitt law. Scaling the existing Hubble constant value determined by Riess et al. (2019), our new calibration implies a value of 71.0 +/- 2.5 km/s/Mpc for a Gaia parallax zero point between 0.029 mas and 0.046 mas.

Orateur: Louise Breuval (Observatoire de Paris, LESIA)

Breuval_Elbereth.pdf

16:00 Electromagnetic radiation from wave turbulence driven by electron beams in solar plasmas

Solar radio bursts of Type III are believed to result from a sequence of physical processes ultimately leading to electromagnetic wave emissions near the electron plasma frequency and its second harmonic. The radiation bursts are due to energetic electron beams accelerated during solar flares. When propagating in the solar corona and the interplanetary wind, these fluxes excite Langmuir and upper-hybrid wave turbulence, which can be further transformed into electromagnetic radiation. It is believed that, in a homogeneous plasma, Langmuir turbulence evolves due to three-wave interaction processes. Large-scale 2D3V Particle-In-Cell simulations have been performed with the fully kinetic code Smilei, using parameters typical of Type III solar radio busts. The excitation of upper-hybrid wave turbulence by energetic electron beams propagating in magnetized plasmas leads ultimately to electromagnetic emissions near the fundamental and the harmonic plasma frequencies.

Orateur: Gaetan GAUTHIER (LPP)

Presentation_ElberethGG.pdf

16:15 → 16:45 Coffee break

16:45 → 17:15 Talk

16:45 High angular resolution study of the Super Stellar Cluster population in IRAS 17138-1017

Using GeMS-Gemini high angular AO-aided imaging in the near-IR, together with a radiative transfer code, we study the population of Super Stellar Clusters (SSCs) in terms of age, extinction, mass and luminosity. We detect with a fair degree of confidence 54 SSCs of mKs between 15 mag and 22 mag with a median photometric accuracy of 0.14 mag. When plotted on a color-color diagram and a color-magnitude diagram, it appears that most of the sources are much extinct with respect to an unreddenned theoretical evolutionary track. The result points unambiguously to two distinct and very recent starburst episodes, at 2.8 and 4.5 Myr. While the SSCs in the 4.5 Myr starburst are distributed along the spiral arms, the 2.8 Myr SSCs are concentrated in the central region. The luminosity function presents a classical power-law behaviour, with however a slope which is shallow compared to other LIRGs. Comparison with radiative transfer simulations shows that especially for the youngest SSCs, the thermal emission by dust is not negligible and could explain the few very red SSCs that could not be dereddened safely. This effect could lead to an misevaluation of the age of the starburst by at most one or two Myr.

Orateur: Tung Lam Nguyen (LESIA, Observatoire de Paris)

High angular resolution study of the Super Stellar Cluster population in IRAS 17138-1017.pdf

17:00 Chemical composition and optical constants of Pluto aerosol analogues

Pluto’s tenuous atmosphere is mainly composed of molecular nitrogen N2 and methane CH4, with 515 ± 40 ppm of carbon monoxide CO (Lellouch et al., 2017, Young et al., 2018). This atmosphere is the place of a complex photochemistry producing aerosols that surround Pluto as several thin haze layers extending at more than 350 km of altitude (Cheng et al., 2017, Gladstone et al., 2016, Stern et al., 2015, Young et al., 2018). These aerosols can deeply affect Pluto’s atmospheric chemistry and climate. For instance, the aerosols can deplete from the atmosphere small hydrocarbons to form more complex molecules (Luspay-Kuti et al., 2017). They can also serve as cloud condensation nuclei (Lavvas et al., 2016, Luspay-Kuti et al., 2017) or cool the atmosphere by absorbing solar radiations (Zhang et al., 2017).
Laboratory simulation is one way to support these hypotheses and constraint the formation pathways, the chemical composition or the physical properties of Pluto’s aerosols. Thus, we produced analogues of Pluto’s aerosols, using the PAMPRE experimental setup (Szopa et al., 2006) developed at LATMOS (Guyancourt, France). As the CH4 mixing ratio strongly varies all along the atmospheric column (Young et al., 2018), different types of analogues were synthesized, in variable proportions of N2 and CH4, with 500 ppm of CO; the idea being to mimic aerosols formed at different altitudes in Pluto’s atmosphere.
The chemical composition of these analogues was inferred from infrared spectroscopy, high-resolution mass spectrometry and elemental composition analyses. Their optical constants (refractive indices and absorption coefficients) were determined by spectroscopic ellipsometry.

Orateur: Lora Jovanovic (LATMOS)

17:15 → 18:00 Invited talk: Luc Blanchet

jeudi 27 février

09:15 → 10:00 Talk

09:30 Composition of primordial asteroids: remnants of the planetesimal populations and members of the oldest asteroids families

The small bodies of the Solar System represent remnants of the building blocks of the planets. As such, they are our best tracers for the processes that occurred during the earliest history of the Solar System. For instance, asteroids cast light on the planetesimals composition, on the location of the snow line, on the thermal conditions of the early solar System, on planetary migration theories and on the alteration processes acting on the Solar System. They also have a high biological importance, because the bombardment of the planets by comets and asteroids (belonging to the B, C and D spectroscopic classes corresponding to carbonaceous rich asteroids) could have brought some organic material. These objects have a composition that have not change much since their formation. They represent a significant part of the planets' histories and, for Earth, they possibly have delivered organics and volatile materials which might have favored the appearance of life.
To cast light on the planetesimal size distribution and composition, we proposed the ORIGINS project. The latter is based on a new method developed by Delbò et al (2017) : it consists in determining the correlation of points in the plane of the inverse of the diameter (1/D) versus semimajor axis (a). The resulting slope, look like the letter « V » and called V-shapes, indicates family age. Thanks to this method, we had already identify a new 3.5 Gyr old family in the inner belt and around 17 asteroids remnants of the original planetesimals. In the future, this method will be applied to the whole main bet, and we will thus identify and characterize the composition of the primordial asteroids.
This thesis is dedicated to the investigation of the composition of primordial asteroids both members of old families and remnants of the original planetesimals. During the thesis, I will actively participate to the spectroscopic survey in the visible and IR range (0.5-2.4 μm) to characterize the composition of both families’ members and leftover planetesimal. Many observations nights are planed, mainly at the DCT telescope (USA, Arizona), IRTF (USA, Hawaii) and Copernico Telescope (Italy, Asiago).
The goal is to characterize the composition of 120-150 asteroids members of old families and remnants of planetesimals during 2019-2022. We expect to observe several absorption features associated to silicates, aqueous altered minerals, organics, sulphide, and eventually ices. If any, in the 0.4-2.5 μm range, we can detect the presence of a given compound, constrain the mineralogical abundances, the grain size of the compounds, and the global composition of the investigated asteroids. Strong interactions are needed between dynamical and compositional studies to establish families' memberships of asteroids. In fact, compositional homogeneity of family members is one of the working hypothesis needed to separate members of a given family from background objects. For this reasons, composition and physical properties such as albedo are fundamental parameters both to characterize the composition of a family and strengthen or reject family memberships.
Moreover, to enlarge the available sample of data, we will use the low-resolution spectra from ESA's Gaia space mission (BP-RP instruments), which will be released in early 2021. Several tens of thousands of asteroids should have Gaia visible spectra (0.4-1 μm range). This thesis work will provide fundamental clues on the compositional gradient and on the size distribution of the primordial planetesimals across the asteroid main belt.

Orateur: Jules Bourdelle de Micas

Elbereth_2020.pdf

09:45 X-ray plateaus in GRB light-curves from jets viewed slightly off axis

The X-ray light-curves of gamma-ray burst afterglows commonly feature phases of shallowly decaying or constant flux lasting from hundreds of seconds to a day, known as plateaus. Correlations exist between observable properties of the plateau and of the prompt emission for bursts with plateaus. Over the years, the origin of these plateaus has been tentatively traced to various mechanisms. These models may reproduce observed correlations, but their physical motivation remains elusive, in particular for those which require variable activity from the central engine. We show that X-ray plateaus can occur due to purely geometrical effects and that the observed correlations naturally arise from these, provided the burst's jet is laterally structured and viewed with an angle close to its core. We illustrate our work by comparing simulated to observed X-ray light-curves, and study other consequences of our interpretation of these plateaus.

Orateur: Raphaël Duque (Institut d'Astrophysique de Paris)

duque_thursday_9h45.pdf

10:00 → 10:30 Invited talk: AFA

10:00 AFA

Far more than an association serving solely its own members, the Association Française d'Astronomie (AFA), recognised as promoting the public interest, acts to enable and motivate the public to take an interest in the sciences of the Universe. By discovering and sharing knowledge, it aims to help citizens play an active role in their education. Through astronomy, it tries to develop curiosity, reasoning and critical thinking in an interdisciplinary and intercultural approach. Founded in 1947 as a popular education movement, AFA networks astronomy-related locations (such as clubs, night stations, astronomical training centers) and offers training to everyone, ranging from the youngest children to adults, including its own animators. It publishes the Ciel&Espace magazine, produces digital resources (websites, podcasts, videocasts...) and organises events such as the Rencontres du Ciel et de l'Espace or the Festival des 2 Infinis. AFA initiates and coordinates numerous awareness actions like Nuit des Etoiles or Paris sous les Etoiles, supports social actors who set up astronomical activities in their neighbourhood (Ciel des Quartiers)...Each year, AFA’s actions reach more than 250,000 people.

Orateurs: Nicolas Franco (AFA), Milan Maksimovic (AFA)

AFA_Elbereth_2020.pdf

10:30 → 11:00 Coffee break

11:00 → 12:00 Talk

11:00 Exoplanets transit spectroscopy with James Webb Space Telescope : From detection to characterization.

Since the first exoplanet detection in 1995, more than 4000 planets have been discovered. In the past tweny five years, the observations tools have greatly improved, increasing the statistics and revealing the diversity of planets. With the upcoming space telescopes such as James Webb and Ariel, detailed knowledge of exoplanet atmospheres will become possible. This opens up new challenges in data treatment, to detrend the signal of planet’s atmosphere from other sources of signal, especially systematic noise and drifts from the instrument. Good knowledge and modelling of these characteristics are necessary, in addition to that of the astrophysical properties. To meet this challenge, new methods are being developed in the community. In order to evaluate their performances and to study the ultimate performance of the instrument, we created realistic synthetic observations. This includes detailed astrophysical properties, as well as the detector response and the systematic behaviour of the instrument. This work allows us a better understanding of the influence of the instrument’s behaviour on the data quality and sensitivity of the observation. With this information, we can investigate which physical properties of the star and the planet are significant for the expected performance. The synthetic data produced will be used for the MIRI-ERS data challenge next year.

Orateur: Marine Martin-Lagarde (CEA-Saclay)

2020Elbereth_MartinLagarde.pdf

11:15 Mercury's ionized exosphere: Global structure and ion dynamics

The Mercury plasma environment is enriched in heavy ions from photo-ionization of the neutral exosphere. The time-of-flight spectrometer FIPS onboard the MESSENGER spacecraft has detected many planetary ion species, of which He$^{+}$, the Na$^{+}$-group (including Na$^{+}$, Mg$^{+}$ and Si$^{+}$) and the O$^{+}$-group (including O$^{+}$ and several water group ions) are the most abundant. Previous models of the planetary ion distribution inside Mercury's magnetosphere have concentrated on the abundant Na$^{+}$ and H$^{+}$ ion populations. Comparison with FIPS data has been limited to the first two MESSENGER flybys. We have developed a test-particle model which describes the full 3D distribution of several planetary ion species which are derived from the neutral exosphere. The global ion density and energy distribution of Na$^{+}$, O$^{+}$ and He$^{+}$ will be presented here. We will also describe the orbital evolution of the Na$^{+}$ ion density.

Orateur: Elisabeth Werner (LATMOS)

werner_elisabeth_elbereth_2020.pdf

11:30 Latest calibration results from QUBIC: The Q&U Bolometric Interferometer for Cosmology

QUBIC is an experiment dedicated to the measurement of polarization B-modes of the Cosmic Microwave Background (CMB) using the novel technology of Bolometric Interferometry. Thanks to its unique spectroimaging capabilities, QUBIC will also be a powerful instrument to constrain foreground contamination. The technical demonstrator has been tested and the concept of this new instrument has been validated.
In this talk, I will first explain the instrument architecture, focussing on the optical design. Some of the calibration results will be presented, showing that we actually have a working bolometric interferometer.
The unique design of QUBIC brings new possibilities to CMB polarization mapping including self-calibration and spectroimaging.

Orateur: Louise Mousset (APC)

Elbereth2020.pdf

11:45 TES detection-chain operation of the QUBIC instrument dedicated to the CMB observation

Q U Bolometric Interferometer for Cosmology (QUBIC) is a new ground-based experiment aiming to detect the Cosmic Microwave Background (CMB) B modes. QUBIC is based on bolometric interferometry, a new instrument architecture. This combines together the well known control of systematic effects from interferometers with the high sensitivity of bolometric detectors. It will observe the polarisation of the CMB, the first light emitted after the Big Bang, in two frequency bands (150 and 220 GHz.)\
QUBIC has two focal planes equipped with kilo-pixel arrays of Transition Edge Sensors (TES). Superconducting QUantum Interference Devices (SQUID) are used as amplifiers and switches for the
multiplexing system. Application Specific Integrate Circuits are used at low temperature for the readout electronics.\
The original concept combining SQUID multiplexing and additional multiplexing in a cryogenic integrated circuit (ASIC) achieves a 128-multiplexing factor. \
The full readout system is in operation in the QUBIC cryostat since 2018 operating on a partially populated focal plane of 256 NbSi
TES. Operations and performance using this readout system will be presented. Aliasing noise and limitation of the multiplexing frequency will also be discussed, highlighting possible future improvements.

Orateur: Guillaume Stankowiak (APC)

Elbereth.pdf

12:00 → 13:30 Lunch break

13:30 → 14:15 Talk

13:30 20 years of ACE data: how superposed epoch analyses reveal generic features in interplanetary CME profile

Interplanetary Coronal Mass Ejections (ICMEs) result from solar eruptions occurring in our star's atmosphere. These large-scale magnetised structures propagate in the interplanetary medium where they can be probed by spacecraft. Depending on their speed, ICMEs may accumulate enough solar wind plasma to form a turbulent sheath ahead of them. They therefore consist of two main substructures, a sheath and a magnetic ejecta (ME), with the magnetic ejecta being the main body of an ICME where the magnetic field intensity is larger, and its variance smaller, than that of the ambient solar wind. We present a statistical study using the superposed epoch analysis technique, of 400 ICME parameter profiles (the magnetic field intensity, the speed, temperature, ...) seen at 1 AU by the ACE spacecraft. This study allow us to build the typical profile of ICME close to the earth. These profiles can then be compared to the future results of the simulation of an ICME propagation into the interplanetary medium from the Sun to the earth thanks to a 3D MHD code.

Orateur: Florian REGNAULT

Talk_elbereth.pdf

13:45 Ultra-Long Gamma-Ray Bursts detection with SVOM/ECLAIRs

Ultra-long Gamma-Ray Bursts (ulGRBs) are Gamma-Ray Bursts (GRBs) with an unusually long emission in X and gamma rays, reaching durations of thousands of seconds. They could form a specific class of high-energy transient events, whose origin is still under discussion. The current sample of known ulGRBs consists of a few 10s of events which have been detected so far by the Burst Alert Telescope (BAT) aboard the Neil Gehrels Swift Observatory and some other instruments. The SVOM mission which is scheduled to begin operations after 2021 could help to detect and observe more ulGRBs thanks to its soft gamma-ray telescope ECLAIRs. After an introduction on ulGRBs and the SVOM mission, we present the results of our simulations on the capabilities of ECLAIRs to detect ulGRBs. First we use the sample of ulGRBs detected by Swift/BAT and simulate these events through a model of the instrument and the prototype trigger software that will be implemented onboard ECLAIRs. Then we present a study of the ECLAIRs capabilities to detect a synthetic population of ulGRBs built by transporting the ulGRBs detected by Swift/BAT to higher redshifts. Finally we give an estimate of the ulGRB rate expected to be detected by ECLAIRs and show that it could be at least a factor 1-2 higher than the one of Swift/BAT, mainly thanks to the long-duration times scales of up to 20 min foreseen to be used onboard ECLAIRs in its image trigger, as well as to the low energy threshold of the instrument of 4 keV, which permits to enhance the detection capability of soft spectrum and hence potentially redshifted GRBs.

Orateur: Nicolas DAGONEAU (CEA/Saclay - IRFU/DAp/LISIS)

Ultra-Long Gamma-Ray Bursts detection with SVOM.pdf

14:00 Search for gamma ray bursts with the X-ray telescope of the SVOM satellite: development and characterization of the on-board scientific software

On August 17, 2017, a gravitational-wave event is detected by the LIGO and Virgo interferometers. For the first time, the signal is associated to the merger of two neutron stars. Two seconds after that, a gamma ray burst is detected by the Fermi satellite, inaugurating the multi-messenger astronomy. Many more of these events are expected to be detected in the future. The scientific results from multi-channels analysis will be unprecedented. Multi-messenger astronomy
will rely on a network of gravitational-wave interferometers (LIGO-Virgo-KAGRA), on many ground-based and space telescopes, and on high-energy neutrino detectors.
In this context, the SVOM satellite aims at detecting and characterizing gamma ray bursts starting at the end of 2021. On board, the MXT (micro-channel X-ray telescope) telescope is designed to localize the burst sources with a precision below 1’ within a few seconds. In my thesis I am involved in developing and implementing the scientific software algorithm on-board for MXT.

Orateur: Shaymaa HUSSEIN (IJCLab)

HUSSEIN_Elbereth_conference.pdf

14:15 → 15:00 Invited talk: Carole Larigauderie

15:00 → 15:30 Coffee break

15:30 → 16:30 Talk

15:30 Unsupervised Machine Learning Algorithms to Detect CO2 Clouds on Mars

The Mars Orbiter Laser Altimeter (MOLA) was an instrument aboard the Mars Global Surveyor spacecraft whose first goal was to dress a precise map of Mars’ topography using laser altimetry. However, precisions of the range measurments were better than expected and allowed detection of features that could not be assigned to the surface. In particular, MOLA was the first instrument to detect polar winter CO2 ice clouds. Previous studies in the early 2000s showed that some laser returns were clearly clouds signatures coming from the atmosphere. These studies were limited due to the large amount of data to analyse that forced them to use very strict distinction criteria. Nowadays, modeling clouds is a huge challenge for the developed Mars Climate Models. Especially, CO2 clouds are exotic components of the Mars’ atmosphere that imply rethinking our microphysical theories. Therefore, it would be important to acquire additional information from the rare, available datasets, leading to a better understanding of involved processes.

K-means clustering methods appear as good options to analyse MOLA data. We proceed by applying the method on a single data file (about 10 % of data) then enlarging to the whole data set. We first guess the best observed parameters among those given in the raw data to separate surface and clouds returns. Then we use three independant optimisation methods, elbow, gap statistic and average silhouette, to determine the best number of clusters. From those clusters, we can eventually plot geographical and temporal distribution of the different clusters separately.

Following the Neumann and al. paper (2003), we find that the product of surface reflectivity and two-way transmissivity of the atmosphere is the best parameter for distinguishing cloud and surface returns. Our three optimisation methods converge to an unique number of five clusters for our test case using only 10 % of the data. Plotting the clusters shows that one of them clearly identifies clouds returns. Another one could represent cloud boundaries or thinner clouds. The other clusters allow for identification of noise and surface returns. Our method allows us to find more clouds than previous studies due to less stringent detection criteria, and eventually new types of clouds. Geographical and temporal distributions resulting from this study should be more accurate and help us understanding cloud formation process on Mars. This dataset will be very important for comparing with microphysical model results in particular in the polar winter season.

Orateur: Vincent Caillé

Présentation elbereth Vincent CAILLE.pdf

15:45 Development and characterization of novel CCD readout electronics for the search of dark matter with DAMIC-M

Despite plenty of evidence for the existence of Dark Matter (DM), no experiment has ever managed to capture it directly. In the last decades, the Weakly Interacting Massive Particle (WIMP) paradigm, the most popular among the DM models, has proven unsuccessful experimentally in a variety of detection methods in the GeV-TeV mass range. DAMIC-M (DArk Matter In CCDs at Modane) will aim to directly search for light WIMPs (<10 GeV/c^2) and hidden-sector DM, using a tower of scientific-grade Charge-Coupled Devices (CCDs) of a kg-size total target mass. In addition, by implementing the Skipper readout technique, a sub-electron energy resolution can be achieved. A fundamental feature of this undertaking will be the development of an acquisition system for the overall control and readout of the CCDs. I will present preliminary results from the evaluation of novel readout electronics including the front-end CCD ReadOut Chip (CROC), which will provide a pre-amplification on the output signal and improve the Signal-to-Noise Ratio, and a new Analog-to-Digital Converter board, allowing for a fast and high-resolution data acquisition.

Orateur: Georgios PAPADOPOULOS ({CNRS}UMR7585)

GPapadopoulos_DAMICM_Elberth2020.pdf

16:00 Visible and Near Infrared spectral analysis of several hollows on Mercury

Among the unexpected features revealed by MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission on the surface of Mercury, geological units named hollows are the most surprising and least understood. Possibly related to volatile components, hollows are small depressions, surrounded by bright halo, never observed on other body in our Solar System. The multispectral images taken by the Mercury Dual Imaging System (MDIS) onboard the probe show that hollows have spectral slope in the visible less steep than the average surface of Mercury. Moreover, an absorption band around 600 nm have been reported in several hollows from multispectral data. Because the multispectral camera are composed of only 10 filters, the spectral analysis is limited. I will present the results of a spectral analysis of several hollows from observations done by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) onboard MESSENGER operating with more than 230 channels.

Orateur: Océane Barraud (LESIA, Observatoire de Paris-PSL)

Elbereth_2020.pdf

16:15 The dusty torus surroung NGC 1068's active nucleus observed with GRAVITY

A significant number of Active Galactic Nuclei (AGN) are known to be heavily obscured: the strong UV-X emission arising from the accretion disk and the associated broad emission lines cannot be directy observed. It is now commonly accepted that this obscuration is due to a structure surrounding the central engine, called the dusty torus. This torus is known to be made of gaz and dust, to be clumpy and to be parsec-scale.
I present my modelling of NGC 1068's dusty torus, constrained with a GRAVITY observation. This instrument is incredibly well designed for such a study: its spectral range (K band, 2.0 - 2.4 microns) is very sensitive to the hot dust at ~1500K which is present in the inner region of the torus, and more importantly its incredibly high angular resolution (up to 4 mas) allows to fully resolve the dusty torus.
Our analysis reveals a structure significantly different from what was expected.

Orateur: Pierre Vermot (LESIA)

Elbereth.pdf

16:30 → 17:00 Coffee break

17:00 → 17:15 Talk

17:00 Search of intermediate mass black holes as dark matter using gravitational microlensing.

Gravitational microlensing constrains massive compact object abundance within the Galactic halo. Past surveys (MACHO, EROS, OGLE, MOA) excluded objects lighter than 10 solar masses as a major component of Galactic dark matter. Recent detections of coalescences of heavier black holes by LIGO/Virgo rekindled the interest in compact objects dark matter. The efficiency of the past microlensing surveys was limited in lens mass by their duration. As they cover several distinct time periods, combining all their databases allows us to obtain very long timescale light curves. As a consequence, we can increase our sensitivity to lenses of mass up to several hundreds of solar masses. I will present and discuss preliminary results from the combination of MACHO and EROS surveys.

Orateur: Tristan Blaineau (LAL)

pr_sentation_ELBERETH.pdf

17:15 → 18:00 Invited talk: Antoine Strugarek

vendredi 28 février

10:00 → 12:00 Visit of the Observatory of Paris

Orateur: Nicolas Lesté-Lasserre

11:00 → 12:00 IAP Seminar: Anthony Challinor

Anthony Challinor
Institute of Astronomy, University of Cambridge, Cambridge, Royaume-Uni
« Backlighting the dark universe with the cosmic microwave background »
Invited by : BOUCHET François and CODIS Sandrine
http://www.iap.fr/vie_scientifique/seminaires/resumes.php?nom_seminaire=Seminaire_IAP&numero=3521

Orateur: Anthony Challinor (Institute of Astronomy, University of Cambridge)

12:00 → 13:30 Lunch break

13:30 → 14:15 Talk

13:30 A rotating disk from a non rotating cloud: is the angular momentum conserved?

Planet-forming disks are fundamental objects thought to be inherited from large scale rotation, through the conservation of angular momentum during the collapse of a prestellar dense core. We investigate analytically and numerically the possibility for a protostellar disk to be formed from a motionless dense core which contains non-axisymmetric density fluctuations.

We show that the angular momentum in the frame of a stellar object which is not located at the center of mass of the core is not conserved, due to inertial forces. The rotation is thus generated locally by the asymmetry of the collapse. Our simulations quickly produce accretion disks at the small scales in the core. We study the velocity gradients at different scales in the simulation as it is done with observations. This analysis reveals projected velocity gradients of amplitudes similar to the ones observed in protostellar cores, and which directions vary, sometimes even reversing when small and large scales are compared. Our results from simulations without initial rotation are more consistent with recent observations where these complex kinematics patterns appear than when solid-body rotation is initially imprinted. Lastly, we show that the disks formed grow to reach sizes larger than observed ones, before fragmenting. We show that including magnetic field in these simulations reduces the size of the outcoming disks, and prevents them from fragmenting, as showed by previous studies.

In this scenario, large disks are generic features which are natural consequences of the hydrodynamical fluid interactions and self-gravity. These results open a new avenue to explore in our understanding of the early phases of disk formation, since they suggest a fraction of the protostellar disks could be the product of non-axisymmetrical collapse and not resulting from the conservation of large scale angular momentum in rotating cores.

Orateur: Antoine Verliat (CEA/AIM)

Antoine_Verliat_Elbereth_PDF.pdf

13:45 The hunt for GW counterparts with H.E.S.S. in the multi-mesenger era.

The detection of the Gravitational Wave (GW) event GW170817 emanating from the coalescence of a binary neutron star alongside an associated short gamma ray burst triggered one of the largest multi-wavelength search campaigns in history. This led to the detection of several Electromagnetic (EM) counterparts in several bands. In fact, the combination of information provided by different astronomical messengers allows a better understanding of such cataclysmic events and phenomena in the Universe and nowadays, the hunt for counterparts of GW events is triggering increasing interest in the astrophysical communities. The High Energy Stereoscopic System (H.E.S.S.) is an experiment based in the Khomas highlands in Namibia dedicated to the detection of Very High Energy gamma rays. A large portion of the H.E.S.S. observing time is allocated to the follow-up of transient astronomical events with a special interest to GWs. Unlike other transients, GW event localizations cover large portions of the sky ranging from 10s to 1000s of degrees. This is why, in order to optimize coverage and increase the chances of counterpart detection, dedicated follow-up strategies are being developed. In this contribution, I report on the GW follow-up program in the H.E.S.S. collaboration focusing mainly on GW follow-up strategies. I also summarize the outcome of the H.E.S.S. observations during the LIGO/Virgo observing runs and discuss prospects with the future Cherenkov Telescope Array.

Orateur: Halim Ashkar (CEA-Irfu)

Elbereth_Ashkar_GW_HESS.pdf

14:00 Optimisation of the optical follow up of gravitationnal waves events

Gravitational waves from binary neutron star (BNS) coalescence, in association to short gamma-ray burst, opened a new era of multi-messenger astronomy. The identification of the counterpart and its multi-wavelength observations improved our understanding of the physics of strong-field gravity and put some constraints on astrophysical models related to matter during the merger and post-merger phase. With improved sensitivity of the LIGO-Virgo detectors, the year-long third observing run (O3) promises many merging binaries detection with an expected number of BNS mergers in the range 1-50. Therefore an intensive multi-wavelength follow-up of those events with ground and space instruments is performed all around the world.
But the identification of the electromagnetic counterpart of such event is very challenging knowing the wide sky localization area provided by LIGO-Virgo (from few tens of degrees to thousands of degrees) and requires complex observation strategies implying many telescopes. We will present our recent development on galaxies targeting strategies, the building of the Mangrove galaxies catalog and the publicly available tools dedicated to improve the follow up of gravitational waves events.

Orateur: Jean-Grégoire Ducoin (IJCLab)

Elbereth_conf.pdf

14:15 → 14:45 Invited talk: Cateline Lantz

14:15 Cateline Lantz

Je suis astronome-adjointe à l'Institut d'Astrophysique Spatiale (depuis 2018) et je suis spécialisée dans l'étude des surfaces planétaires par spectroscopie visible et infrarouge. En particulier, j'essaye de comprendre les liens entre astéroïdes sombres et météorites carbonées en simulant en laboratoire les phénomènes d'altération spatiale qui agissent sur la surface des petits corps. Je suis impliquée dans les missions de retour d'échantillons Hayabusa-2/JAXA et OSIRIS-REx/NASA. Je m'intéresse également aux processus d'altérations à la surface de Mars en préparant les observations de l'instrument MicroMega qui sera à bord de la mission ExoMars/ESA.

Ces prochaines années nous allons avoir pour la première fois en laboratoire des échantillons d'astéroïdes dits primitifs, c'est à dire avec des traces de carbone et de matière hydratée, grâce aux missions spatiales Hayabusa-2/JAXA et OSIRIS-REx/NASA. Je présenterai quelques résultats marquants des phases d'observations orbitales de ces missions, ainsi que les recherches que j'effectue en laboratoire en support à l'interprétation de leurs résultats.

Orateur: Cateline Lantz (IAS)

14:45 → 15:15 Coffee break

15:15 → 16:00 Talk

15:15 High-energy neutrinos from cosmic ray interactions in the Local Bubble

We study the possibility that a local nearby supernova Vela is responsible for the knee in the cosmic rays spectrum. This source could also explain the excess of IceCube neutrinos with energies E > 100TeV and gamma-ray excess at high Galactic latitudes at energies E > 300 GeV in FermiLat data. Our work takes into account the presence of the Local Bubble which plays the role of a shield for cosmic rays flux and target to produce neutrinos and gamma rays from primordial Vela PeV protons.

Orateur: makarim bouyahiaoui

bouyahiaoui_elberth_28fev_20.pdf

15:30 Relativistic X-ray jets in the black hole candidate MAXI J1820+070

Jets and outflows are observed in a diverse range of accreting systems such as young stellar objects, galactic X-ray binaries and active galatic nuclei. The formation of jets, their propagation and their association with accretion processes are still largely unclear. However, their feedback on their immediate environment is now starting to be quantified, as their interaction with the interstellar medium can be observed using high spatial resolution images of X-ray binaries (e.g. Corbel et al. 2002, Migliori et al. 2017).

Here, we report on the black hole candidate MAXI J1820+070, discovered during its 2018-19 outburst and extensively monitored. Radio observations have revealed the formation of relativistic radio jets on both sides of the system (Bright et al. 2020). To constrain the high energy emission from these jets, we conducted four X-ray observations with the Chandra X-ray Observatory between 2018 November and 2019 May. Simultaneously, MAXI J1820+070 was monitored in radio with the VLA and MeerKAT.

The observations reveal the presence of X-ray moving sources associated to the radio counterparts of the jets. The jets are travelling at apparent relativistic velocities, with a possible deceleration at late time, which could be due to shocks with the surrounding environment. In addition, the broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated up to very high energies (above 10 TeV) during shocks, probably between the jets and the interstellar medium. MAXI J1820+070 is the third black hole X-ray binary for which such an interaction is observed at high energy.

Orateur: Mathilde Espinasse (AIM / CEA)

Espinasse.pdf

15:45 FIRST: going above the resolution limit of a telescope for substellar companion characterization

FIRST (Fibered Imager foR a Single Telescope) is an original instrument dedicated to imaging substellar companions at high contrast and high angular resolution in the visible. Its principle is based on the pupile remapping technique, which turns a monolithic telescope into an interferometer. Thanks to the monomode filtering operated by the optical fibers and an appropriate beam recombination scheme, this method allows the detection of companions at angular separations shorter than the diffraction limit of the telescope. In addition, the interferometric recombination of FIRST is coupled with a spectrometer, allowing the spectral characterization of the detected companions, a unique capability at such spatial scales.
A first version of the instrument has been installed on the Subaru Japanese 8m-telescope, in Hawaii. An upgraded version, FIRSTv2, is currently under development at LESIA and includes instrumental modifications in order to increase its sensitivity. The main modification consists in the integration of an innovative integrated optics chip to perform the interferometric recombination. In particular, this electro-optic component provides an on-chip mean to modulate the phase at high frequency, opening new observing mode possibilities.
In this presentation I will explain all these aspects of this instrument and talk about my thesis project: characterize the second version of this instrument, integrate it at the Subaru telescope and astrophysical exploitation of it.

Orateur: kevin barjot (LESIA)

20200228_Elbereth_Barjot.pdf

16:00 → 16:30 Invited talk: SpaceBus

16:00 Présentation de SpaceBus France

SpaceBus France est une association Loi 1901 à but non lucratif créée en 2017 et gérée bénévolement par des docteur.e.s en astronomie. Les objectifs de notre association sont de :

• faire découvrir l'astronomie et la science de manière ludique au grand public grâce à des animations ludiques et interactives,
• former à la démarche scientifique et créer des vocations,
• créer un lien entre professionnels, amateurs et grand public,
• promouvoir la place des femmes dans les sciences,
• sensibiliser à la protection environnementale.

Pendant un mois, chaque été, sous la forme d'un évènement itinérant gratuit, nous traversons une région différente de France, en passant de ville en ville, pour aller à la rencontre des locaux et vacanciers. Nous proposons à une trentaine de professionnel.le.s en astronomie (doctorant.e.s, chercheurs.es, ingénieur.e.s) de nous rejoindre au cours de cet évènement afin d'animer, en journée, différentes animations sur le Système Solaire, les météorites, le réchauffement climatique, les croyances populaires en astronomie ou dans les films de science-fiction, etc. Le soir, des associations locales d’astronomie nous rejoignent pour des observations de la Lune et des planètes.

Depuis deux ans, cet événement estival rencontre un vif succès avec plus de 19 000 visiteurs en 30 villes et une centaine d’apparition dans les médias. Cette année, pour notre troisième tournée, SpaceBus France va arpenter les côtes de la Manche entre Rennes et Rouen du 25 juillet au 21 août 2020 !

Au cours de l’année, en dehors de la tournée estivale, SpaceBus France est sollicité pour participer à des festivals scientifiques destinés au grand public et/ou aux scolaires : 80 ans du CNRS, Fête de la Science, Festival Star’s Up, …

Si vous souhaitez transmettre votre passion au grand public en animant bénévolement des ateliers et/ou en proposant de nouvelles animations, rejoignez-nous en adhérant à l’association SpaceBus France !

Plus d’informations sur nos réseaux sociaux ou notre site internet : www.spacebusfrance.fr

Orateurs: Dr Raphaël Peralta (CEA DAp/AIM), Dr Diane Bérard (LESIA), Dr Mathilde Gaudel (LERMA)

16:30 → 17:00 Coffee break

17:00 → 18:15 Talk

17:00 Influence of EUV flux variations on the precipitating ion flux from MAVEN observation

At present epoch, the efficiency of Mars' atmosphere sputtering by heavy ion precipitation to induce atmospheric espace is expected to be negligible under actuel solar wind conditions. It is presently difficult to directly measure its current influence on Mars atmosphere. However, it is possible to better understand the potentiel importance of this process alonf Mars' history by further constraining the precipitating ion flux thanks to MAVEN instruments. We study the influence of the solar Extreme Ultra-Violet (EUV) flux intensity on the precipitating ion fluxes as seen by MAVEN/SWIA, an energy and angular ion spectrometer. We defined three periods with significantly different EUV flux intensity (1.6 and 3.2 times the lowest EUV intensity) and compare the precipitating ion flux measured by MAVEN/SWIA during each period. At low energy [30-650] eV, we find that the median (average) precipitating ion flux during the medium and low EUV periods are respectively 1.7 and 3 times more intense than the flux during the high EUV period. At high energy [650-25000] eV, a similar trend in the intensity of the precipitating ion flux is observed but with an increase by 50% and 70% respectively. A larger EUV flux does therefore not seem to favour heavy ion precipitation into Mars' atmosphere, contrary to modelling prediction and overall expectations.

Orateur: Antoine Martinez (LATMOS)

Presentation_Martinez_Antoine_Elbereth_2020_V000.pdf

17:15 Deflectometry applied to freeform and large optical surface metrology

Deflectometry is a slope acquisition metrology process for specular surfaces. The large dynamic of spatial frequency measured as well as the in-situ capabilities of deflectometry makes it a promising complementary metrology tool in the optical fabrication context.
However, systematic errors in low frequency shape reconstruction, prevent deflectometry from being an independent metrology process, as well as high frequency errors due to the shape reconstruction inversion and propagation of non linear display error through Phase Shift algorithm.
To achieve high frequency independent measurement, we have developed models of propagation through data processing algorithms, from which we designed bias robust inversion algorithms.
We present here these new algorithmic approaches and experimental results which demonstrates their efficacy (in comparison to interferometry measurements).

Orateur: Hugo Jonquiere (ONERA)

Présentation_y2_HJO_pdf.pdf

17:30 Multimessenger signals from core-collapse supernovae

The final step of the life of a massive star is its collapse and explosion creating a supernova. During the collapse phase, several phenomena happen in the core of the star before the observed explosion. One of these phenomena is the development of instabilities. The collapse creates a shock wave that becomes stationary $\sim$150 km away from the surface of the proto-neutron star (PNS). All the instabilities developing between the shock and the core of the PNS modulate the signal emitted in gravitational waves (GW) and neutrinos.
The aim of my PhD thesis is to study all the instabilities evolving within the sphere delimited by the shock. I started my PhD studying the outermost instability. The matter immediately under the shock interacts with the neutrinos emitted by the neutrinosphere. The neutrinos heat up the matter and trigger convection due to the Rayleigh-Taylor instability. This instability plays a crucial role in pushing the shock outward closer to the explosion threshold, producing GW and modulating the emission of neutrinos. I analyse the ratio between buoyancy and advection time scales in this region. Indeed, the Rayleigh-Taylor instability competes with the advection that tends to stabilise the process. I take a new look at the current stability criterion established in 2006. A new criterion is established by distinguishing several length scales: the size of the unstable domain limited by the shock position, the size of the most buoyant region and the density scale-height.

Orateur: Anne-Cécile Buellet

Presentation_Elbereth.pdf

17:45 Development of a Closed Cycle Dilution Refrigerator for future astronomical missions

The use of stable sub-Kelvin coolers is a key technology in order to reach the highest sensitivity that astrophysical space missions can offer. Historically, few instruments (e.g. Planck HFI or Hitomi SXS) required temperature down to 100 mK. Currently, two technologies can provide such temperatures in a space environment: ADR (Adiabatic Demagnetization Refrigerator) and OCDR (Open Cycled Dilution Refrigerator). For CMB observations, the next generation of satellites (e.g. LiteBIRD) will require the highest stability and continuous temperature operation. For now, only the OCDR can reach such requirements but with a limited lifetime as this cooler is making use of a limited quantity of He3 and He4 isotopes which mixture is then wasted in space. Planck-HFI observations were then limited to 2.5 years.
I am working on the design and development of a new dilution system (CCDR - Closed Cycle Dilution refrigerator) for which the He3-He4 mixture will be recycled and separated in order to avoid large quantities of helium to be embarked and to extend the sub-K cooler lifetime.

Orateur: Valentin Sauvage

18:00 Water ice clouds in the Martian atmosphere during the 2018 Global Dust Storm

Water ice clouds have been observed in the Martian atmosphere since 1972, but as recent studies have shown their important role in the martian climate there is a growing need to better characterize the properties of water ice aerosols with observational constraints.

The Atmospheric Chemistry Suite (ACS) instrument onboard the ExoMars Trace Gas Orbiter (TGO) ESA-Roscosmos mission began science operations in March 2018. Here we use the Solar Occultation IR observations in the 3 µm region of the Mid-Infrared (MIR) channel to monitor the water ice clouds in the Martian atmosphere before and during the 2018 Global Dust Storm, and retrieve their particles sizes.

Orateur: Aurélien Stcherbinine (IAS / LATMOS)

Elbereth_2020_Stcherbinine.pdf

18:15 → 19:00 Invited talk: Benjamin Charnay

19:00 → 22:00 Closing buffet / party