Gaspard Duchêne

  Assistant Research Astronomer and Lecturer

   Astronomy Department
   C-203 Hearst Field Annex    UC Berkeley
   Berkeley CA 94720-3411 USA
   gduchene (at)          Fax: (510) 642 3411



   Publications / CV (pdf)

   AST/EPS C12 (The Planets)

   UC Adaptive Optics Seminar
Stellar multiplicity and star formation
Stellar multiplicity is ubiquitous among all types of stars in our Galaxy. The observed multiplicity properties (frequency, distributions of semi-major axes and mass ratios, ...) of populations of young stars can be used to infer the end result of star formation and, more specifically, to constrain the process of fragmentation of prestellar cores. I conduct high resolution imaging surveys of objects ranging from brown dwarfs to O-type stars in star-forming regions and young open clusters. In recent years, I have moved towards the study of the multiplicity of embedded protostars, which offer the best chance to determine the outcome of the star formation process unaltered by subsequent dynamical evolution.

In-depth studies of selected multiple systems
Some young multiple systems are highly valuable as benchmarks or particularly unique systems. I conduct a variety of dedicated follow-up studies on selected systems, using imaging, photometry and spectroscopy. Determining accurate individual masses for pre-main sequence stars in order to test evolutionary models is one of my objectives. I also study the presence and properties of circumstellar disks in multiple systems, with an eye on the general topic of planet formation within multiple systems. Finally, I regularly work on the so-called "infrared companion" phenomenon, i.e., systems in which a T Tauri star appears to be paired with an embedded protostar, an apparent paradox in the framework of coeval systems.
Imaging of protoplanetary and debris disks
Circumstellar disks around pre-main sequence stars represent the birthplace for planetary systems. On the other hand, the debris disk phenomenon occurs after planet formation, when collisions between large planetesimals produce short-lived small dust grains in a gas-poor environment. Both types of disk inform us on planet formation, either from an initial conditions or end result standpoint. My work in this area focusses on obtaining high-resolution imaging datasets that help resolve the spatial structure and determine the dust properties, in particular the distribution of grain sizes, of a variety of disks. To gain as complete a picture of a disk as possible, I combine scattered light images from HST and adaptive optics instruments with continuum thermal imaging with millimeter interferometer arrays. This combination allows to simultaneously study grains that range several decades in size as well as the entire disk structure.
Radiative transfer modeling of disks
Full quantitative analyses of the high-quality imaging datasets I gather on specific disks require the use of a radiative transfer model. To this end, I have contributed to the development of the Monte Carlo-based MCFOST radiative transfer code to produce synthetic disk observations. This code yields scattered light images, thermal emission maps and spectral energy distributions (including a complete treatment of polarization) and allows for the use of both parametric and user-specified disk structures and dust contents. I use MCFOST to probe dust grain growth and vertical settling within protoplanetary disks as well as the detailed geometrical structure and dust porosity in debris disks. Typically, I run vast grids of (tens or hundreds of thousands of) models spanning a broad parameter space before narrowing down on a preferred disk model.

Last updated: 20 July 2011