Over the past decade multi-wavelength observations have revealed the extraordinary ubiquity and diversity of star formation in galaxies, ranging over billionfold ranges in star formation rates (SFRs), whether expressed in absolute terms, or in terms of areally or mass-normalised SFRs. Considerable attention has been focussed on the high-density extremes in starbursts and galactic nuclei, but much can be learned as well from star formation in low-density regimes-- in the outermost discs of spiral galaxies, and in early-type galaxies, low surface brightness galaxies, and extreme dwarf galaxies. This talk will highlight recent observations of star formation in these disparate environments, and examine the common behaviours and physical clues that they reveal.
Mot(s) clés libre(s) : galaxies, Star formation

Only about a hundred years ago astronomers came to recognize cosmic explosive events. What was once termed as Stella Nova are now divided into two major families, novae and supernovae (with real distinct classes in each). The variables and the explosions have been interesting in their own right and contributed richly to key problems in modern astrophysics: distances to galaxies and cosmography. The area of transient and variable stars is once again undergoing a renaissance due to wide field optical surveys. The Palomar Transient Factory (PTF) was designed explicitly to chart the transient sky with a particular focus on events which lie in the nova-supernova gap. With its innovative two-telescope architecture it achieves both high cadence and large areal rate of coverage. PTF was commissioned during the summer of 2009. PTF is now finding an extragalactic transient every 20 minutes and a Galactic (strong) variable every 10 minutes. Spectroscopy undertaken at Keck and Palomar has allowed us: identify an emerging class of ultra-luminous supernovae, discover luminous red novae, undertake UV spectroscopy of Ia supernovae, discover supernovae powered by something other than Nickel-56, clarification of sub-classes of core collapse and thermo-nuclear explosions, map the systematics of core collapse supernovae, a trove of eclipsing binaries and many others.
Mot(s) clés libre(s) : Supernovae, Spectroscopy, Stars

The massive black holes found at the centers of most galaxies, including our own, are believed to be the ashes of the fuel that powered quasars early in the life of universe. I will briefly review some of the astronomical evidence for these objects and then describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant dynamical relaxation, phase transitions, and lopsided stellar disks.
Mot(s) clés libre(s) : galaxies, Black holes, Star formation, Stellar dynamics