Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères

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LERMA Detailed Presentation

12 January 2019

LERMA presentation

LERMA (Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres) is a research entity operated by CNRS and 3 higher education institutions: Observatoire de Paris (OP), (...)

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11 January 2019

Management team

Director: Jean-Hugues FILLION
jean-hugues.fillion @ sorbonne-universite.fr
Deputy Director: Franck LE PETIT
franck.lepetit @ obspm.fr
Technical Director : Jean-Michel KRIEG (...)

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11 January 2019

Administrative team

The administrative team of LERMA is composed of 7 agents who work closely with the administrative services of the CNRS (Ile de France-Meudon delegation (DR5) and INSU), the Paris Observatory (...)

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29 October 2014

Main partners and collaborations

LERMA develope numerous collaborations both national and international
Major agencies and institutions in charge of space missions and major ground-based facilities having collaborations with (...)

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Séminaires à venir

Vendredi 26 avril 2019, 14h00
Salle de l'atelier, Paris
The Effect of Gravitational Lensing on Cosmological Parameter Estimation
résumé :
A long standing question in cosmology is whether gravitational
lensing by structure biases the apparent distance or the mean flux
density of sources. Interest in this has been rekindled by recent
calculations in 2nd order relativistic perturbation theory which
suggest significant implications for cosmological parameter
estimation from both supernovae and the microwave background. In
this talk I shall first review the somewhat confusing history of
the subject, going back to the early '60s and including both
Weinberg's 1976 argument that there should be no effect on grounds
of flux conservation and the general relativistic "focusing theorem"
of the '80s that seems to contradict this and which foreshadows the
more recent results. I then describe recent work with John Peacock
where we have shown how these conflicts are resolved. Regarding
Weinberg we show that there is a loophole in his argument, and
lensing does in fact bias the apparent distance, but it is a very
small effect. We show that the apparent intrinsic tendency for
structure to cause focusing of light rays that emerges from the
focusing theorem is a statistical rather than a physical effects.
Vendredi 21 juin 2019, 14h00
Salle de l'atelier, Paris
Accretion-driven turbulence and observational signatures
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