Calendar

Sep
26
mer
Clément Baruteau — Observational predictions of the presence of giant planets in the dust’s radio emission of protoplanetary discs @ Univers 21
Sep 26 @ 11 h 00 min – 12 h 00 min
Séminaire

The classical picture of protoplanetary discs forming smooth, continuous structures of gas and dust has been challenged by the growing number of spatially resolved observations. These observations indicate that radial discontinuities and large-scale asymmetries may be common features of the emission of protoplanetary discs, and they are often interpreted as signatures of the presence of (hidden) planets. They stress the need to better understand how disc-planets interactions generally, and planetary migration more specifically, impact the dust’s thermal emission in protoplanetary discs. In this talk, I will report our recent and ongoing efforts in predicting the dust’s radio emission in protoplanetary discs due to the presence and migration of massive gap-opening planets, via two-fluid (gas+dust) hydrodynamical simulations post-processed with radiative transfer calculations. I will show how these predictions apply to the discs around AB Aurigae and MWC 758.

Oct
3
mer
David Smith — Faint Gamma-ray Pulsars @ Univers 21
Oct 3 @ 11 h 00 min – 12 h 00 min
Séminaire

In its 11th year on orbit, the Fermi LAT continues to discover GeV gamma-rays from
about 24 pulsars per year. The most sensitive way to find them is to use rotation ephemerides
to « phase fold » the gamma photons, to then look whether the resulting
phase histogram is flat or not. We have done this for over a thousand radio pulsars,
using ephemerides provided by the Nancay, Jodrell Bank, and Parkes radio telescopes.
I will present sixteen gamma-ray pulsars we found, and explain how they enhance the sample
of over 220 pulsars we already had. I will discuss possible causes of the gamma-ray
« deathline » near a spindown power of Edot ~ few 1E33 erg/s.
Finally, I will say some words about extrapolating the observed gamma-ray pulsar
population to estimate the contribution of unresolved pulsars to the diffuse background.

Oct
10
mer
Didier Fraix-Burnet : Unsupervised classification: exploring the high dimension @ Univers 21
Oct 10 @ 11 h 00 min – 12 h 00 min
Séminaire

Dealing with large amount of data  is  a new problematic task in astrophysics. One may distinguish the management of these data (astroinformatics) and their scientific use (astrostatistics) even if the border is rather fuzzy. Dimensionality reduction  in both the number of observations and the number of variables (observables) is necessary for an easier physical understanding. This is the purpose of classification which has been traditionally eye-based and essentially still is but this becomes not possible anymore. In this talk, I present a general overview of machine learning approaches for unsupervised classification, with applications to stars (chemical abundances) and galaxies (spectra).

Nov
7
mer
César Gattano : Séminaire LAB @ Univers 21
Nov 7 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Nov
21
mer
Benoit Commercon : séminaire LAB @ Univers 21
Nov 21 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Nov
27
mar
Thibault Cavalié — Séminaire LAB @ Univers 21
Nov 27 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Déc
5
mer
Andréa Bertoldi: Séminaire LAB @ Univers 21
Déc 5 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Jan
16
mer
Nathalie Ysard : Séminaire LAB @ Univers 21
Jan 16 @ 11 h 00 min – 12 h 00 min
Séminaire

TND

Fév
13
mer
Cécile Engrand: The composition of interplanetary and cometary dust @ Univers 21
Fév 13 @ 11 h 00 min – 12 h 00 min
Séminaire

Small bodies have escaped planetary accretion and have best preserved the composition of the matter initially present in the solar nebula. Cosmic dust originates from these small bodies, asteroids and comets. Interplanetary and cometary dust are collected on Earth in places with a low accumulation rate of terrestrial dust, like the polar caps or the stratosphere. Interplanetary dust particles (IDPs) have been collected in the stratosphere by NASA for a few decades. A fraction of IDPs (at least) are proposed to be of cometary origin. Cosmic dust from the polar caps are larger than IDPs and are called micrometeorites. We collect micrometeorite at the Concordia Antarctic station at Dome C since 2000. The Concordia collection contains very pristine samples, including particles that are dominated by organic matter and that are very probably cometary. Spatial missions like Stardust (NASA), Hayabusa (JAXA) and Rosetta (ESA) also gave access to the structure and composition of asteroidal and cometary dust. Stardust brought back dust particles from comet 81P/Wild 2, but the collection occurred at high relative velocity (6 km/s) and the samples were altered during the collection. The Rosetta mission collected dust particles from comet 67P/Churyumov-Gerasimenko at much lower velocity (1-10 m/s), but the analyses had to be performed in situ onboard the Rosetta orbiter by the dust instruments (GIADA, COSIMA, MIDAS). The Hayabusa mission returned samples from asteroid Itokawa, which is an asteroid related to ordinary chondrites. At least two future spatial missions are bound to bring back samples from carbonaceous asteroids: Hayabusa 2 (JAXA, asteroid Ryugu) et OSIRIS-REx (NASA, asteroid Bennu). The CAESAR mission is also currently under study to bring back a sample from comet 67P/Churyumov-Gerasimenko.
The presentation will summarize the present knowledge on the composition of interplanetary and cometary dust, based on the results of laboratory analysis of dust particles collected on Earth, and of spatial missions.