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Protoplanetary discs across the stellar mass range


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Type

Thesis

Change log

Authors

Boneberg, Dominika Maria Rita 

Abstract

In this thesis, I discuss two studies concerned with modelling protoplanetary discs around stars from different ends of the stellar mass range. In Chapters 1 and 2, I give an introduction to the field of protoplanetary discs, both from an observational and a modelling point of view, and describe the radiative transfer methods I have employed.

In Chapter 3, I present my work regarding the disc around the Herbig Ae star HD 163296. I show the results of applying a new modelling technique to this disc: I combine SED modelling with fits to the CO snowline location and C18O J=2−1 line profile from ALMA. I find that all of the modelling steps are crucial to break degeneracies in the disc parameter space. The use of all of these constraints favours a solution with a notably low gas-to-dust ratio (g/d<20). The only models with a more interstellar medium (ISM)-like g/d require C18O to be underabundant with respect to the ISM abundances and a significant depletion of sub-micron grains, which is not supported by scattered light observations. I propose that the technique can be applied to a range of discs and opens up the prospect of being able to measure disc dust and gas budgets without making assumptions about the g/d ratio.

In Chapter 4, I present my work on characterising the disc around the very low mass star V410 X-ray 1. Protoplanetary discs around such low mass stars offer some of the best prospects for forming Earth-sized planets in their habitable zones. The SED of V410 X-ray 1 is indicative of an optically thick and very truncated dust disc, with my modelling suggesting an outer radius of only 0.6 au. I investigate two scenarios that could lead to such a truncation, and find that the observed SED is compatible with both. The first scenario involves the truncation of both the dust and gas in the disc, perhaps due to a previous dynamical interaction or the presence of an undetected companion. The second scenario involves the fact that a radial location of 0.6 au is close to the expected location of the H2O snowline in the disc. As such, a combination of efficient dust growth, radial migration, and subsequent fragmentation within the snowline leads to an optically thick inner dust disc and larger, optically thin outer dust disc. I find that a firm measurement of the CO J=2−1 line flux would distinguish between these two scenarios by enabling a measurement of the radial extent of gas in the disc. Many models I consider contain at least several Earth-masses of dust interior to 0.6 au, suggesting that V410 X-ray 1 could be a precursor to a system of tightly-packed inner planets, such as TRAPPIST-1.

In Chapter 5, I summarise the work presented in this thesis, give an overview of future applications of the methods outlined in this dissertation, and an outlook on potential future projects.

Description

Date

2018-03-29

Advisors

Clarke, Cathie J.
Ilee, John D.

Keywords

astronomy, planet formation, protoplanetary discs, ALMA

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
STFC