Feb 20

"Short Circuits: Lightning in Protoplanetary Disks"
Alexander Hubbard, American Museum of Natural History, New York, NY

Observations of accretion disks around young stars have multiplied enormously over the past decade. Even so, the physical scale that the observations inform us of is large, and they have not allowed us to falsify models of how the accretion flow itself is generated. An alternative source of evidence for the small scale structure of protoplanetary disks is the examination of chondritic meteorites, and they tell us that the protosolar nebula was a wild and active place. I will describe an instability which can explain some of the constraints posed by chondrules by rapidly heating regions of the disk from 850K to above 2000K in a process very similar to both electrical short circuits and lightning. This research shows that planet formation scenarios cannot afford to assume that protoplanetary disks are spatially and temporally homogenous, and must instead embrace a more exciting environment.

Mar 6

"Frontier Science with the James Webb Space Telescope"
Jason Kalirai, Space Telescope Science Institute (STScI)

The James Webb Space Telescope (JWST) will be the most powerful space telescope that astronomers have ever constructed, and it is a critical step towards answering the top science questions outlined in the recent Astronomy 2010 - 2020 Decadal Survey. In this talk, I will begin by summarizing the current status of the JWST project and some of the recent milestones that have been achieved, including the completion of all of the JWST mirror segments and the delivery of the first science instruments from international partners to NASA. I will then discuss a wide range of fundamental science cases that are uniquely enabled by JWST's unprecedented sensitivity (10 minute exposures will detect M dwarfs with V = 30 at S/N = 5) and superb resolution (diffraction limited at 2, 4, and 7+ microns). These include core science drivers which have strengthened during the past decade (e.g., the characterization of exoplanet atmospheres and the search for molecular signatures of life) and new discovery areas that have recently emerged (e.g., establishing a 1% error on H_o and constraining dark energy). I will also summarize several synergistic science investigations that will become possible by combining future wide field surveys from WFIRST and LSST with JWST spectroscopy.

May 1

"Doppler Tomographic Observations of Exoplanetary Transits"
Marshall Johnson, University of Texas at Austin

Transiting planet candidates around rapidly rotating stars, a number of which have been found by the Kepler mission, are not amenable to follow-up via the usual radial velocity techniques due to their rotationally broadened stellar lines. An alternative method is Doppler tomography. In this method, the distortions of the stellar spectral lines due to subtracted light during the transit are spectroscopically resolved. This allows us to not only validate the transiting planet candidate but also to obtain the spin-orbit misalignment for the system. The spin-orbit misalignment is a powerful statistical tracer of the migration histories of planets. I discuss our project to perform Doppler tomographic observations of Kepler candidates and other transiting planets using the facilities at McDonald Observatory. I present our first transit detection, that of Kepler-13 b, and discuss some other recent results.