LESIA - Observatoire de Paris

Sauf exception, les séminaires ont lieu sur le site de Meudon, dans la salle de conférence du bâtiment 17.

Prochains séminaires

  • Jeudi 20 septembre 2018 à 16h00 (Salle de conférence du bâtiment 17)

    The many ’faces’ of the molecular torus of NGC1068

    Santiago García-Burillo (OAN)

    We have used ALMA to image with 0.03-0.04"(2-3pc) spatial resolution the emission of a set of molecular lines, including CO(2-1), CO(3-2) and HCO+(4-3), and their underlying continuum emission in the circumnuclear disk of NGC1068, covering a region that extends from r=200pc down to the central 7-10pc-diameter torus of this prototypical Seyfert 2 galaxy, which was first detected in the 6-5 line of CO by García-Burillo et al 2016. These new observations, by using three lines spanning three orders of magnitude in densities, reveal the many ’faces’ of the molecular torus in NGC1068. The torus shows a stratified layered structure spanning a radial range that goes from r=2-3pc to r=10pc. The kinematics of molecular gas in the torus are characterized by strong non-circular motions and enhanced turbulence. Furthermore, the CO(2-1) line emission has allowed us to image the outflowing molecular gas component emerging from the torus. A far-reaching question, to be answered by ongoing ALMA surveys of nearby AGNs (NUGA, GATOS), is whether similarly perturbed and turbulent tori are expected to be found ubiquitously in Seyfert galaxies, and if their properties should change as a function of parameters like the AGN luminosity, the degree of obscuration, or the Eddington ratio.

  • Lundi 24 septembre 2018 à 11h00 (Salle de réunion du bâtiment 14)

    Recent Results from Snapshot Spectroscopic Imaging studies of the Sun at m-wavelengths

    Atul MOHAN (Tata Institute of Fundamental Research, Pune, India)

    The talk will focus on the study of weak energy release events in the Corona using the powerful new technique of snapshot spectroscopic imaging with Murchison Widefield Array (MWA). MWA observes the Sun in a frequency range of 80- 240 MHz at a spectro-temporal resolution of 40 kHz and 0.5 s. We imaged two 4 min long and 15 MHz wide band datasets at 0.5s and 16kHz resolution. This was a period of very low solar activity as per the metrics of high energy observations. This lead to nearly 46,000 images which were converted to brightness temperature maps. I will brief the techniques we employ to extract useful physical information from such large volume of data spread across 4 axes, namely 2 angular sky coordinates, frequency and time. I will focus on one of the events we studied and the interesting physical inferences.