Although I originate from Devon, since 2015 I have lived in Cambridge, where I studied Natural Sciences for my BA and MSci degrees, specialising in astrophysics.

I also enjoy doing outreach and public engagement; for several years now I have been part of the committee of Cambridge Hands-On Science (CHaOS), a student-run group which runs hands-on roadshow events in schools and public events around the country.

In what spare time remains, I enjoy heading out into the countryside for long walks, or relaxing with a cryptic crossword.

Contact/Links

Email:
ads79@cam.ac.uk

GitHub:
https://github.com/AndrewSellek

CV:
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Disc environments evolve through a number of competing processes; my particular interests are on the secular (i.e. long term) evolution, addressing questions such as:

1. What is the origin of any winds that are removing material; does photoevaporation affect discs in important ways?
2. How long are the resulting protoplanetary disc lifetimes; how is this affected by their surroundings?
3. Where does their material end up – on the star, blown away in a wind, or in planets?

Broadly speaking, I tackle these questions in three ways:

– Firstly, by seeking to improve our physical understanding of photoevaporative winds including what heats and cools them, and what controls the structure of these thermal winds.
– Secondly, by investigating how photoevaporative winds compete with other evolutionary processes in the disc such as viscous accretion and radial drift of dust. I combine models of these effects in a forward modelling process to try to reproduce trends we see in demographic surveys of protoplanetary discs.
– Finally by producing synthetic observations of winds from our models that can be compared to observations.

Some recent highlights (as of October 2022) of accepted first-author papers that I have published during my PhD include:

We explore the difference between different simulations of photoevaporative winds in terms of their spectra. We show that the ability of X-rays to heat a wind may be limited by attenuation or by cooling, with the balance leading to an optimum energy of a few 100 eV for typical atomic coolants. Hence much of the disagreement between models can be explained by the shape of the spectrum. We assess quantitatively what changes in heating luminosity and cooling rates would do to the ability of X-rays to drive a wind.

We extend previous self-similar models, considering in particular the effects of temperature gradients, which only make small differences, and elevated wind bases, which are more important. We explain results of hydrodynamics simulations – which generally agree well with our solutions – in terms of space-filling, and consider implications for [Ne II] line profiles.

We consider how the radial drift of dust grains lowers disc masses enough to better explain this correlation, and find that a fairly weak photoevaporative wind is needed to reproduce low accretion rates.