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

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Proto-étoiles, disques & jets

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Jets protostellaires : propriétés chimiques et dynamiques

Au stade protostellaire, les effets combinés de la rotation et du champ magnétique conduisent à la formation de jets lancés dans l’environnement immédiat des embryons stellaires. L’étude de ces jets et des flots moléculaires qui tracent l’interaction des jets avec le milieu ambiant, apporte des informations incomparables sur le processus de formation des étoiles. Nous étudions en particulier les chocs associés à ces jets, les phénomènes physiques et chimiques associés, qui permettent de remonter aux processus d’accrétion.

Disques de débris dans les systèmes planétaires

Un disque protostellaire et formé en même temps que la proto-étoile, dont l’évolution se poursuit en parallèle de celle de l’objet protostellaire. L’étude de ces disques autour des étoiles jeunes apporte des clés pour comprendre la formation des planètes.

Formation des étoiles massives

Séminaires à venir

Vendredi 21 décembre 2018, 14h00
Salle de l'atelier, Paris
Astrochemistry in star forming regions : new modeling approaches
Emeric BRON
résumé :
Star-forming regions present rich infrared and millimeter spectra emitted by the gas exposed to the feedback of young stars. This emission is increasingly used to study the star formation cycle in other galaxies, but results from a complex interplay of physical and chemical processes : chemistry in the gas and on grain surfaces, (de)excitation processes of the atoms and molecules, heating and cooling balance,... Its understanding thus requires detailed astrochemical models that include the couplings between these processes. In this talk, I will present several examples where new modeling approaches of specific processes and their couplings proved crucial to solve persistent observational riddles : from the driving role of UV irradiation in the dynamics of photodissociation regions (PDR) to the efficient reformation of molecular hydrogen in these regions.
Mardi 15 janvier 2019, 11h00
Salle de l'atelier, Paris
ATTENTION jour ET heure inhabituels
Thresholds for Globular Cluster Formation and their Dominance of Star Formation in the Early-Universe
IBM Research Division
résumé :
Young massive clusters (YMCs) are usually accompanied by lower-mass clusters and unbound stars with a total mass equal to several tens times the mass of the YMC. If this was also true when globular clusters (GCs) formed, then their cosmic density implies that most star formation before redshift ~2 made a GC that lasted until today. Star-forming regions had to change after this time for the modern universe to be making very few YMCs. Here we consider the conditions needed for the formation of a ~10^6 Msun cluster. These include a star formation rate inside each independent region that exceeds ~1 Msun/yr to sample the cluster mass function up to such a high mass, and a star formation rate per unit area of Sigma_SFR ~ 1 Msun/kpc^2/yr to get the required high gas surface density from the Kennicutt-Schmidt relation, and therefore the required high pressure from the weight of the gas. High pressures are implied by the virial theorem at cluster densities. The ratio of these two quantities gives the area of a GC-forming region, ~1 kpc^2, and the young stellar mass converted to a cloud mass gives the typical gas surface density of 500-1000 Msun/pc^2. Observations of star-forming clumps in young galaxies are consistent with these numbers, suggesting they formed today's GCs. Observations of the cluster cut-off mass in local galaxies agree with the maximum mass calculated from Sigma_SFR. Metal-poor stellar populations in local dwarf irregular galaxies confirm the dominant role of GC formation in building their young disks.
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