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Marc White - Astrophysicist - The Australian National University
Research

The outflows driven by forming protostars provide important clues to the nature of the star formation process.

 

My research focuses on observations and analysis of the outflows driven by actively-accreting protostars. I'm looking to answer the following questions:

  • How are the outflows being driven?
  • What are the physical properties of the outflow?
  • Can we trace the outflow characteristics to a launch point on the circumstellar disk?
  • Are interactions between the outflow and the surrounding molecular cloud material affecting the outflow properties, and injecting momentum into the cloud core material?

My work to date has used the Near-infrared Integral Field Spectrograph (NIFS) on Gemini North, Mauna Kea, Hawaii. Built by my home institution, The Research School of Astronomy and Astrophysics of The Australian National University, NIFS is a fantastic instrument for doing protostellar outflow work. Because it is a spectroimager, we can acquire both spatial (structural) and spectral (kinematics) information simultaneously. This allows us to track multiple outflow components across an image of the outflowing material. The adaptive optics system at Gemini North allows us to achieve 0.1 arcsec spatial resolution.

Once we have acquired our data, we use a variety of techniques to analyse the outflows. To being with, we often see two outflow components with differing velocities superimposed over each other. We use statistical testing to separate the line emission from each component. We can then analyse each component separately, by looking at their luminosities, velocities and densities (via infrared [Fe II] line ratios) as a function of position. This allows us to probe the physics that is occurring internal to the outflows.

We then build analytical models to explain the variations in the physical parameters of the outflows. Because our data traces outflow structure and dynamics over a wide field, we are in a unique position to provide new insights into protostellar outflows. In brief, we have found the following features in the outflows of the young stellar object DG Tauri:

  • A stationary recollimation shock in the approaching jet, implying a larger jet terminal velocity than previously thought;
  • Moving knots in the jet channel, which move more slowly than previously thought;
  • The presence of velocity variations in the jet;
  • A low-velocity approaching outflow component, which is consistent with being a turbulent entrainment layer between the jet and a wide-angle molecular wind;
  • A receding outflow with a strikingly different morphology to the approaching outflow, which we model as an obscured counterjet.
Some of these features have been suggested before. However, my work is the first time that they have all been put together to create a coherent global picture for the outflows from a young stellar object. If you'd like to know more, feel free to take a look at my papers and posters.