Observatoire de Paris Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Sauf exception, les séminaires ont lieu sur le site de Meudon, dans la salle de conférence du bâtiment 17.

S’abonner aux mises à jour de cette page :

Séminaires passés

  • Vendredi 10 décembre 2021 à 11h00 (Salle de conférence du bâtiment 17 et Visioconférence)

    Théorie de la diffusion cohérente et incohérente en fréquence

    Véronique Bommier (LESIA)

  • Vendredi 26 novembre 2021 à 11h00 (Salle de réunion du bâtiment 14)

    Turbulence dans le vent solaire : multifractalité et ondelettes

    André Mangeney

  • Jeudi 25 novembre 2021 à 16h00 (Salle de réunion du bâtiment 16 et Visioconférence)

    Probing Unique Regimes of Exoplanet Science with Interferometry at CHARA and VLTI

    Tyler Gardner (University of Michigan)

    Current detection limits struggle to find exoplanets around hot (A/B-type) stars. Searching for planets in this regime provides crucial information on how planet occurrence rate scales with stellar mass. We are carrying out an interferometric survey to discover au-regime giant planets via differential astrometry orbiting individual stars of sub-arcsecond binary systems. The combination of milli-arcsecond resolution with stable wavelength calibration provides precision at the few tens of micro-arcsecond level in short observations at CHARA/MIRCX and VLTI/GRAVITY. This allows us to detect the wobble of a star from orbiting companions down to a few Jupiter masses. I will present the status of our survey, including newly detected tertiary stellar companions. We show that we are beginning to probe down to planetary masses. I am also involved with efforts to measure the orbit-dependent spectra of "hot Jupiter"-type exoplanets with interferometry, which can place useful constraints on atmosphere circulation models. I will present our first promising candidate detection, along with prospects for the future of characterizing close-in exoplanets with this technique.

    Lien pour assister au séminaire :

  • Lundi 22 novembre 2021 à 16h00 (En visioconférence)

    The signature of planet migration in transit-timing variation

    Jean Teyssandier (Université de Namur)

    Planetary systems containing two or more planets sometimes appear to exhibit resonant configurations, where the period ratio between the planets is close to the period ratio of two small integers. These configurations enhance dynamical interactions between the planets, which can be detected by variations in the time of transits of individual planets (the so-called TTVs). In addition, resonant configurations are commonly thought to be the result of convergent migration, a process by which young planets migrate in a gaseous discs at different speeds so that the outer planet "catches up" with the inner one and captures it in a resonance. In this talk, we will demonstrate what is the imprint of disc migration on the TTV signals that are observed today. We will focus on two systems, K2-24 and Trappist-1, and link their current architecture to their past history.

    Pour assister au séminaire

    Avec CarbonFreeConf (qui vous donne accès à plus de fonctionnalités) :

    Avec Zoom :

  • Jeudi 18 novembre 2021 à 14h00 (Amphithéatre Evry Schatzmann batiment 18)

    Transport of chemical elements in stars : Lithium abundance dispersion in metal-poor stars

    Morgan Deal (Instituto de Astrofísica e Ciências do Espaço (IA))

    The formation and evolution of light elements in the Universe act as important cosmological constraints. The oldest stars of the Galaxy have long been assumed to display in their outer layers the primordial lithium abundance, although all studies of stellar physics proved that this abundance must have decreased with time. The primordial Li abundance deduced from the observations of the Cosmological Background is indeed larger than the maximum one observed in these stars. Recent observations gave evidence of a large Li abundance dispersion in very metal poor stars.

    During this presentation, we show that the amount of depletion needed to solve the lithium problem, can be accounted for a large part by the transport processes of chemical elements in stars. We show that stellar models including non-standard transport processes such as the rotation-induced mixing and penetrative convection are able to explain the lithium surface abundances of Population II stars, when using a lithium initial abundance in accordance with the primordial lithium abundance obtained from latest BBN results.

    We also address the general question of the lithium abundance dispersion obtained from observations of carbon enhanced metal-poor stars, and how the interplay of atomic diffusion and accretion of matter modifies the element abundances in these metal-poor stars. In particular, we focus on the hydrodynamic processes that could take place after accretion. We show that the observations of lithium dispersion, associated with carbon enrichment, are well accounted for in terms of accretion onto the metal-poor stars, with accreted masses smaller than a few Jupiter masses, when using a primordial initial lithium abundance.

  • Jeudi 28 octobre 2021 à 16h00

    The Keck Planet Imager and Characterizer capabilities : Imaging Exoplanets and the Galactic Center

    Jacques-Robert Delorme (AO Scientist - Keck)

    The Keck Planet Imager and Characterizer (KPIC) is a purpose-built instrument to demonstrate technological and instrumental concepts initially developed for the exoplanet direct imaging field. Located downstream of the current Keck II adaptive optic (AO) system, KPIC consists of multiple upgrades : new coronagraphs for NIRC2, an infrared Pyramid wavefront sensor and a fiber injection unit (FIU) capable of combining the high-contrast imaging capability of the AOs system with the high dispersion spectroscopy capability of the current Keck high resolution infrared spectrograph (NIRSPEC). Deployed at Keck in September 2018, this instrument has already been used to image and acquire high-resolution spectra (R > 30,000) of multiple targets of interest. In the near term, it will be used to spectrally characterize known directly imaged exoplanets and low-mass brown dwarf companions visible in the northern hemisphere with a spectral resolution high enough to enable spin and planetary radial velocity measurements as well as Doppler imaging of atmospheric weather phenomena. In this presentation, I will present the new capabilities offered by KPIC as well as some of its first science results.

    Lien pour assister au séminaire :

  • Lundi 25 octobre 2021 à 11h00

    Exploring the near-Earth asteroid diversity : the ANIME CubeSat mission concept

    Davide Perna (INAF - Observatoire de Rome)

    The “Asteroid Nodal Intersection Multiple Encounters” (ANIME) mission concept has been developed in response to the 2020 Italian Space Agency (ASI) call for ideas for future CubeSat missions. ANIME aims to explore three near-Earth asteroids (NEAs), selected by virtue of their peculiar and yet unexplored size and physical regimes, as well as their relevance in terms of planetary protection. Thanks to an optimized trajectory, the targets are encountered during their passages through their orbital nodes. The 12U ANIME spacecraft will flyby two “potentially hazardous asteroids”, and then rendezvous in 2028 with baseline target 2000 SG344. This 40-m-sized asteroid is an order of magnitude smaller than previously visited ones, and its study will allow us to constrain the latest theories about planetary system formation scenarios, addressing questions about the monolithic vs. cohesive vs. rubble-pile aggregation structure of small asteroids.

    I will present and discuss the ANIME mission concept, which has been developed by a team from Italian INAF observatories and universities.

    Pour assister au séminaire :

    Avec CarbonFreeConf :

    Avec Zoom :

  • Lundi 4 octobre 2021 à 16h00 (En visioconférence)

    Comparison between laboratory reflectance spectroscopy and simulated unresolved observations of primitive small bodies

    Sandra Potin (LESIA)

    Reflectance spectroscopy is a common tool used to retrieve physical and mineralogical information on Solar System planetary bodies. However, the reflectance spectrum of a surface depends on several parameters, including the illumination condition and observing geometry. The observed reflectance of small bodies is generally compared to laboratory measurements of meteoritic samples or terrestrial analogues to assess the composition and alteration history of the target’s surface.

    Laboratory measurements are performed in a controlled environment, where the composition and texture of the sample are known and the illumination and observing geometry is fixed. However, if the spectroscopic observations of the small body are unresolved, its reflectance is integrated over the whole observed surface, which averages spatial compositional and textural heterogeneities and changes in the illumination and observation geometries due to both the shape of the object and the topography of its surface (slopes, craters, …).

    First I will highlight the effects of the illumination and observation geometry on the reflectance spectra of meteorites. Then I will compare reflectance spectra acquired in the laboratory and simulated unresolved observations of small bodies. Finally I will discuss the limits of the comparison between meteorites and small bodies.

    Pour assister au séminaire :

    Avec CarbonFreeConf (qui vous donne accès à plus de fonctionnalités) :
    www.carbonfreeconf.com/join-conference/273/pDJyIzSESoG8ZDum3zQxZZRYINrllF (si vous avez déjà un compte, alors un "sign in" suffit. Sinon, il vous suffit de faire "register")

    Avec Zoom :

  • Vendredi 1er octobre 2021 à 11h00 (En visioconférence avec Zoom)

    Cassini at Jupiter : radio emissions and magnetospheric dynamics

    Philippe Zarka (LESIA)

    This seminar deals with the results obtained with Cassini’s radio instrument (built in LESIA - actually DESPA) during the Jupiter fly-by of 2000-2001. First I will briefly recall the flux calibration of the data and the results on Jupiter’s radio components, their spectrum, power and and beaming obtained and published in 2004. Then I will focus on new results just accepted in the JGR, obtained from the same data but including also this time the polarization information. These results concern the physical relationship between auroral radio components, the localization of their source in Jupiter’s magnetosphere, and the relative control of their variations by the planetary rotation and by the solar wind. With this work, we have tried (and hopefully succeeded) to reduce the entropy of the complex Jovian radio zoo. The next stepinvolves modeling via the ExPRES code developed in LESIA. Our results provide a frame to interpret the present radio observations by Juno and the future ones by JUICE, and a firmer ground to extrapolate our understanding of the Jovian magnetosphere to astrophysical systems (exoplanets).

    Lien pour assister au séminaire :

  • Lundi 27 septembre 2021 à 16h00 (En visioconférence)

    De CH4 à HCl en passant par HDO et H2O : 3 ans de recherche active des gaz trace martiens par le spectromètre ACS sur TGO

    Franck Montmessin (LATMOS)

    Le Trace Gas Orbiter (TGO) de l’ESA est le premier volet du programme de l’ESA ExoMars.
    L’orbiteur a atteint Mars en octobre 2016 et a achevé sa phase d’aéro-freinage en mars 2018 après laquelle la mission scientifique de TGO a pu démarrer. L’objectif majeur de TGO est de détecter, cartographier et remonter aux sources de gaz traces, dont certains pourraient être révélateurs d’une activité résiduelle géophysique, voire même biologique, sur Mars ; le plus emblématique d’entre eux étant le méthane. A bord de TGO, l’Atmospheric Chemistry Suite (ACS) est le spectromètre développé par l’IKI (Moscou) et auquel le LATMOS a été partie prenante. ACS couvre un domaine de longueur d’ondes allant de 0.7 à 15 mm où toutes les espèces gazeuses connues ou attendues sur Mars possèdent une signature diagnostique et offre une résolution spectrale qui n’avait jamais été atteinte par aucune autre mission martienne par le passé.
    Après 3 ans passés en orbite autour de Mars, l’heure est venue de faire un premier bilan du travail exploratoire réalisé par ACS. De ses tentatives répétées de confirmer la présence du méthane à son ébauche de caractérisation du cycle de H2O conjointement à celui de HDO en passant par sa découverte de HCl, ACS et TGO refaçonnent peu à peu notre compréhension des mécanismes physico-chimiques qui régissent la composition et le comportement de l’atmosphère de Mars.
    Ces résultats et leur portée pour la science martienne seront présentés au cours de ce séminaire.

    ESA’s Trace Gas Orbiter (TGO) is the first component of ESA’s ExoMars programme.
    The orbiter reached Mars in October 2016 and completed its aerobraking phase in March 2018, after which the TGO science mission could start. The main objective of TGO is to detect, map and trace back the origin of trace gases, some of which could be indicative of residual geophysical and even biological activity on Mars, the most emblematic of which is methane. On board TGO, the Atmospheric Chemistry Suite (ACS) is the spectrometer developed by IKI (Moscow) and in which LATMOS has been involved. ACS covers a wavelength range from 0.7 to 15 mm where all known or expected gaseous species on Mars have a diagnostic signature and offers a spectral resolution that has never been achieved by any other Mars mission in the past. After 3 years in Mars orbit, it is time to make a first assessment of the exploratory work done by ACS.
    From its repeated attempts to confirm the presence of methane, to its tentative characterisation of the H2O cycle in conjunction with that of HDO, to its discovery of HCl, ACS and TGO are gradually reshaping our understanding of the physico-chemical mechanisms that govern the composition and behaviour of Mars’ atmosphere. These results and their significance for Martian science will be presented during this seminar.

    Pour assister au séminaire :

    Avec CarbonFreeConf (qui vous donne accès à plus de fonctionnalités) :
    www.carbonfreeconf.com/join-conference/270/BTegQlMYMuecSKRYKUNgO8xlcmlVqn (si vous avez déjà un compte, alors un "sign in" suffit. Sinon, il vous suffit de faire "register")

    Avec Zoom :

0 | 10