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2020BallabioGPhD.pdf (17.08 MB)

The Evolution & Dispersal of Planet-Forming Discs

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posted on 2021-04-30, 14:45 authored by Giulia Ballabio
The evolution and eventual dispersal of protoplanetary discs strongly influences the formation of planetary systems. In the standard picture, the dynamics of the gas surface density of young circumstellar discs is controlled by viscous accretion while the late evolution and final dissipation is dominated by star-driven photoevaporation.
In the first part of this work I focus on modelling dust and gas spatial distribution within discs, using hydrodynamic simulations. I initially develop a new numerical algorithm to control the dust evolution consistently and more accurately in SPH simulations (using the code PHANTOM). I then apply this approach to the modelling of a real system. In particular, I look at the disc around HD 143006, which shows a surplus of morphological features. I find that only a scenario including both a misaligned binary and a planetary companion further out in the disc can explain all the substructures observed in both the dust continuum emission (ALMA) and the scattered light image (SPHERE). If confirmed, HD 143006 would be the first known example of a circumbinary planet on a strongly misaligned orbit.
The second part of my thesis concentrates on internal photoevaporation, which is currently accepted as an important player in the late evolution of discs. Thermally driven winds have been unambiguously detected through blue-shifted emission lines, but their detailed properties remain uncertain. Here, I present a new empirical approach to produce observational predictions of photoevaporative winds, seeking to Fill the disconnection between theory and observations. I use a self-similar model of an isothermal wind to compute line profiles of several characteristic emission lines, in particular the [Ne ii] line at 12.81 μm, and optical forbidden lines such as [Oi] 6300A and [S ii] 4068/4076A. When combined with the most recent observations (particularly from the VLT), these new diagnostics allow for a better understanding of the origin of the detected emission lines. Interestingly, the results are indicative of a possible origin in a multi-phase wind, i.e. with a thermal and a magnetic components.



Richard Alexander; Chris Nixon

Date of award


Author affiliation

School of Physics and Astronomy

Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD



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