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mars 2018
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No seminar - winter holidays

Vendredi 2 mars 2018 11:00-12:00

No seminar

No seminar - winter holidays

Vendredi 9 mars 2018 11:00-12:00

No seminar


Vendredi 16 mars 2018 11:00-12:00

To directly image and characterize exoplanets, we need advanced optical
systems on current Very Large and future Extremely Large telescopes that
can suppress the bright glare of stars by 6-10 orders of magnitude, and
analyze the feeble light of potential planetary companions. Such
high-contrast imaging systems consist of advanced adaptive optics and
associated wavefront sensing techniques, coronagraphy to (locally)
suppress the diffracted starlight, contrast-enhancing techniques like
angular/spectral/polarimetric differential imaging, and diagnostic
capabilities like (high-resolution) spectroscopy and
(spectro)polarimetry. In our group in Leiden we cover all these
different aspects of high-contrast imaging, with the aim to achieve the
ultimate contrast performance and characterization potential with a
complete, integrated end-to-end system for ground-based telescopes. We
are currently exploiting brand-new liquid-crystal technologies that
offer important performance benefits for many components in a
high-contrast imaging instrument, and for the system as a whole. We have
introduced the “vector-APP” coronagraph that has currently been
successfully commissioned at MagAO, LBT, and SCExAO, and are developing
versions for several other telescopes and instruments, including a
stratospheric balloon telescope. We apply lessons learnt from the
vector-APP to the Vector Vortex Coronagraph to enhance its spectral
range and suppression. Novel versions of the vector-APP now have several
methods for focal-plane wavefront sensing built in, and we are currently
also testing versions of Pyramid and Zernike wavefront sensors with
enhanced performance thanks to liquid-crystal implementations. As
vector-APP coronagraphs are broadband, we are applying them for
integral-field spectroscopy, and developing versions that are optimally
matched to fiber-fed spectrographs. And as the vector-APP is based on
polarization tricks, we are extending it with polarimetric
implementations. We are currently even playing with crazy
liquid-crystal-based Sparse Aperture Masking concepts that are heavily
multiplexed, and can include achromatic nulling. I will provide an
overview of these projects, and an outlook for implementing such
techniques at the VLT and the ELT to ultimately characterize rocky
planets in the habitable zones of nearby stars.

Olivier Witasse (ESTEC) - JUICE : A European Mission to Jupiter and its Icy Moons

Vendredi 23 mars 2018 11:00-12:00

JUICE - JUpiter ICy moons Explorer - is the first large mission in the ESA Cosmic Vision programme. JUICE is due to launch in May 2022. It will arrive at Jupiter in October 2029, and will spend three years characterizing the Jovian system, the planet itself, its giant magnetosphere, and the giant icy moons Ganymede, Callisto and Europa. The spacecraft will then orbit Ganymede for a few months. One of the main goals of JUICE is to explore the habitable zone around Jupiter. Ganymede is a high-priority target because it provides a unique laboratory for analyzing the nature, evolution and habitability of icy worlds, including the characteristics of subsurface oceans. The payload consists of 10 instruments plus a ground-based experiment using the VLBI network. The speaker is the JUICE project scientist and he will explain the mission, the science, the challenges (technical, human), with the help of short videos and animations.

Pratika Dayal (Groningen) - The first billion years of galaxy formation

Vendredi 30 mars 2018 11:00-12:00

Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe : as the first sources of light, these galaxies ended the ’cosmic dark ages’ and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the shapeless ellipticals galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. At the forefront of astronomical research, the past few years have seen cutting-edge instruments provide tantalising glimpses of such galaxies chaotically assembling in an infant Universe. I will show how this data has provided an unprecedented opportunity to pin down the reionization state of the Universe (at least in its last stages), understand their physical properties, and study the key physics driving their formation and evolution. Finally, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope and the associated reionization history, can provide a powerful testbed for Warm Dark Matter models.

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