Calendar

Jan
23
mer
Benoit Commercon — Protostellar disk formation in low- to high-mass star formation @ Univers 21
Jan 23 @ 11 h 00 min – 12 h 00 min
Séminaire

The new generation of interferometers provide unprecedented constraints on the protostellar disk formation process. Observations indicate that most disks have a small extent at the Class 0 stage and that disks grow in size at latter stages. I will present the results of 3D protostellar collapse calculations that cover a wide range of initial mass (from 0.5 to 100 solar mass), as well as different initial rotation and/or turbulence support. The calculations are performed using the RAMSES code, including the effect of non-ideal MHD with the ambipolar diffusion and radiative transfer. I will show how ambipolar diffusion is regulating the disk and outflow formation at the early stages of the class 0 phase. I will discuss the disk properties: magnetisation level, magnetic field lines topology, stability. In a second part, I will present recent work done in the context of the protostar formation (second collapse) where the effects of non-ideal MHD (ambipolar and Ohmic diffusion) are taken into account. I will highlight the differences with previous results obtained with ideal MHD and show to what extent these kind of models can provide constraints on the protostellar evolution (disk, protostar). I will finally present preliminary results of protostellar collapse models which include coupled dust and gas dynamics.

Jan
24
jeu
David Barrado — Gods, heroes and constellations: cosmography and myths in Greek ceramics @ Univers
Jan 24 @ 14 h 00 min – 15 h 00 min
Séminaire

Eratosthenes of Cyrene (276-194 BCE) was one of the great scholars of the Hellenistic period. Responsible for the Library of Alexandria, 

he made fundamental contributions in both Astronomy and Geography. Among the legacy he left to us is the work « Catasterisms » 
(From Ancient Greek καταστερισμός (katasterismós, “star legend”, from καταστερίζω or “to place among the stars”) which describes the celestial
 constellations known at that time and are associated with a myth, by  the rise of the protagonist to the heavens. 
However, the process of defining the constellations began much earlier and some have  their origin in Mesopotamia or Phenicia.
The literature of the Archaic and Classic Periods allows us to reconstruct the creation of new constellations based on Hellenic
 myths and trace both the original Greek contributions and the heritage of older cultures. In this talk, I will present a summary of the process.
Jan
29
mar
Javier Olivares — Bayesian Modeling @ Univers
Jan 29 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Fév
6
mer
Panayotis Lavvas — Séminaire LAB @ Univers 21
Fév 6 @ 12 h 00 min – 13 h 00 min
Séminaire

TBD

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.

Mar
12
mar
Nathalie Ysard — Séminaire LAB @ Salle 306
Mar 12 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD