Depuis le coeur des étoiles jusqu’à leurs environnements proches, la matière est plasma. Sa structure, sa composition et sa dynamique sont gouvernées par le champ magnétique, le rayonnement et les (...)
Magnetic fields in Young Protostellar Disks and Jets, and some Astro-chemistry
Chin Fei Lee
ASIAA, Taiwan
résumé :
Magnetic fields in Young Protostellar Disks and Jets, and some Astro-chemistry
Chin Fei Lee, ASIAA Taiwan
I will present our recent ALMA observations towards 3 young protostellar
systems, reporting the possible field morphology in their disks and jets.
In particular, I will report the field morphology implied from the dust
polarizations and SiO line polarizations, and discuss the possible toroidal
and poloidal fields in the disks and jets. I will also discuss the
formation process and the growth of the protostellar disks, and the possible
magnetic braking that reduces the angular momentum in the envelope.
Interestingly, more than 10 organic molecules including prebiotic molecules
are detected in the atmosphere of one of the disks. I will compare their
abundances to those in the hot corinos around low-mass protostars and touch
on the possible formation mechanism of those molecules. Some of the
molecules seem to be formed on CO icy grains and some in the gas phase.
Vendredi 20 septembre 2019, 14h00
Atelier, Paris
Challenging a Newtonian prediction through Gaia wide binaries
Xavier HERNANDEZ
UNAM, Mexico
résumé :
Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. After reviewing recent work evidencing the existence of a critical acceleration scale in Elliptical Galaxies and Globular Clusters, I will show new results showing such a phenomenology in Gaia wide binaries using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical a0 value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.
