Institute of Astronomy

- Andrew Sellek


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Office: Obs O10
Office Tel: (01223) 766624
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Research Themes: Star Formation and Exoplanets

Research Keywords: Accretion, Planets, Sub-mm, Theory


My research is focussed on understanding protoplanetary discs, the sites of planet formation around young stars. Much of my work particularly involves attempting to understand the contribution that photoevaporation processes make to the evolution and ultimate dispersal of these discs.

Photoevaporation processes involve a radiation source that heats the material at the disc surface, resulting in material leaving the disc in a wind. Internal photoevaporation results from radiation from the central star that the disc orbits, and is thought to be a good way to open up a hole in the inner disc around 1 au from the star. External photoevaporation results from the action of other stars; stars form together in clusters, and larger clusters may contain hot and massive (but shortlived) stars which emit enough radiation to strip material from their neighbours. A prime example of this process can be seen in the proplyd structures in the Orion Nebula, as well as in other slightly less extreme environments such as the Flame Nebula NGC2024 [3].

Most recently, I have been working on understanding what controls the structure and nature of thermally driven disc winds. We tackled this problem in [4] by using self-similar models, extending them to cover a wider parameter space than before. We found that the launch velocities of winds can be understood by considering the space they have to fill - for example, a strongest effect on these velocities can be found by raising the wind base as the winds must curve outwards more rapidly. The solutions have wide applicability to wind models, and thus give us better insights into the mass loss produced by photoevaporation; they should also be useful for more precise future interpretations of observed signatures of winds. Another key aspect I am now working on is the heating and cooling of these winds.

Photoevaporation competes with other processes in the evolution of discs, such as viscous accretion, the radial drift of dust, and planet formation. Some of my other work involves coupling photoevaporation models to disc evolution models in order to understand how these processes interact. For example, in [1], we found that external photoevaporation can remove 10s of % of the dust in the disc, though radial drift ultimately limits this process. This interplay severely reduces the lifetime of dust in these discs, with consequences for planet formation. In [2] we explored how the observed dust masses of protoplanetary discs could help us constrain the rate at which internal photoevaporation can disperse a disc, finding that low rates are preferred, but that it is hard to distinguish otherwise between EUV-driven and X-ray-driven winds.

A connected line of investigation therefore is understanding how the evolution of dust in protoplanetary discs determines their observational properties, attempting to interpret trends seen in clusters and disc demographics. Part of this work involves how the demographics change when photoevaporation is considered. For example, in [1], we found that the although external photoevaporation reduces the lifetime of the discs in both gas and dust, their relative values are largely unaffected by the strength of this process. Moreover, we found that when present, the observed radii of discs are predominantly determined by the strength of the external photoevaporation process, and that this model could successfully explain the sizes of discs around stars forming in the Orion Nebula. In [2] we studied the correlation between the accertion rates and dust masses of discs finding that a combination of radial drift and internal photoevaporation can better explain the spread of the data than discs which evolve by viscous accretion alone.

Selected papers

  1. The evolution of dust in discs influenced by external photoevaporation
    (Sellek A. D., Booth R. A., Clarke C. J., 2020)

  2. A dusty origin for the correlation between protoplanetary disc accretion rates and dust masses
    (Sellek A. D., Booth R. A., Clarke C. J., 2020)

  3. Proplyds in the flame nebula NGC2024
    (Haworth T. J., Kim J. S., Winter A. J., Hines D. C., Clarke, C. J., Sellek A. D., Ballabio, G., Stapelfeldt K. R., 2021) 

  4. The general applicability of self-similar solutions for thermal disc winds
    (Sellek A. D., Clarke C. J., Booth R. A., 2021)


2019 - Present: PhD Student in Astronomy, University of Cambridge

2015 - 2019: BA & MSci Natural Sciences (Astrophysics), University of Cambridge

Page last updated: 12 June 2021 at 15:27