Research
My research focuses on high contrast imaging of circumstellar material: disks, envelopes, jets, and substellar companions. The observational tools that I employ to understand these objects include adaptive optics, coronagraphy, differential polarimetry, mid-infrared imaging, and integral field spectroscopy.High contrast imaging of circumstellar disks
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Collaborators: Karl Stapelfeldt, Deborah Padgett, Caer McCabe, Gaspard Duchene, Christophe Pinte, Paul Kalas, Francois Menard, and others.
Hubble Space Telescope NICMOS Coronagraphic Polarimetry of Disks
Planets form in circumstellar disks. We believe that at young ages, dust grains in disks grow and aggregate into planetesimals, followed by the accretion of gaseous atmospheres onto giant planets. The growth of dust grains in disks around young stars, from sub-micron ISM grains to macroscopic particles to centimeter-sized rocks, is thus a key part of planet formation processes. Multiwavelength imaging and polarimetry lets us probe the earliest stages of this process, by determining the scattering properties of grains, a key diagnostic for grain sizes and compositions.I am currently conducting high-contrast, high spatial resolution, polarimetric imaging of circumstellar disks around a sample of Herbig Ae stars, using the Hubble Space Telescope's NICMOS instrument. The resulting images will be analyzed using sophisticated 3D Monte Carlo radiative transfer models, to determine what physical disk parameters and dust properties give rise to the observed appearance and polarization. These proposed observations will provide a basis for comparison with ongoing HST polarimetry of T Tauri and debris disks, aiding our understanding of how the processes of grain growth scale with stellar mass and age.
Collaborators: Gaspard Duchene, Glenn Schneider, Dean Hines, Carol Grady, John Wisniewski, Christophe Pinte, and others.
Integral field spectroscopy of outflows from young stars
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Studying the acceleration and collimation of jets requires high resolution observations of the immediate circumstellar environments. The necessary observations combine high angular resolution (< 0.1 arcsec ) with moderate spectral resolution (R = 2000 - 4000). Such observations can now be obtained using integral field spectrographs on large telescopes, such as OSIRIS on Keck and GMOS & NIFS on Gemini. Our ongoing observations will investigate the structure and properties of jets across a range of young stellar objects, helping to ascertain how stellar properties such as mass and age influence the resulting outflows.
Collaborators: James Graham, Ben ZuckermanDevelopment of the integral field spectrograph/polarimeter for the Gemini Planet Imager
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Collaborators: James Larkin, James Graham, Bruce Macintosh, Mike Fitzgerald, Christian Marois, and the rest of the GPI Project Team.
Other Projects
The Lyot Project, led by Dr. Ben R. Oppenheimer of the American Museum of Natural History in New York, developed the first optimized diffraction-limited coronagraph for a high order AO system, the Air Force's AEOS telescope on Maui. I developed the infrared science camera, Kermit, which is used with the Lyot Project coronagraph.This page last updated by Marshall on 2007-10-10.