16 May 2013
16 May 2013
Speaker: Adam Kraus (CfA)
Title:Clay Lecture: Giant Planets Caught at Formation
Abstract:The past two decades have seen the establishment and rapid growth of exoplanetary science as a major emphasis in astronomy, fueled by the discovery of hundred of planets by RV surveys and thousands more by Kepler and other transit surveys. However, young directly-imaged exoplanets offer critical tests of planet-formation models that can't be matched by RV and transit surveys of mature stars. These targets have been extremely elusive to date, with no exoplanets younger than ~10-20 Myr and only a handful of directly-imaged planets at all ages, but the first statistically robust samples are now becoming available.
I will describe an ongoing survey which exploits the technique of nonredundant aperture mask interferometry to achieve high-contrast observations at the diffraction limit of large telescopes, extending direct-imaging planet searches outward to the nearest star-forming regions. I recently reported the discovery of LkCa15 b, which is located inside of the known gap in LkCa15's protoplanetary disk and is surrounded by spatially resolved clouds of gas and dust. These features imply that LkCa15 b has been caught as it is being assembled from its natal protoplanetary disk. I will describe the newest observations of the LkCa15 system, the status of our survey program, and the prospects for future searches.
I also have been studying the growing population of planetary-mass companions (M=5-20 MJup) in very wide orbits (a=100-1000 AU) around young stars, which pose a significant challenge to models of both star and planet formation. I have calculated the first measurements of their frequency and mass function, and my collaborators and I are pursuing several followup programs to ascertain their detailed properties and search for circumplanetary disks. In light of these new results, I will discuss our ability to explain these systems as either "extreme planets" or "extreme binary stars".