Research Interests – Discs around forming stars

Dr Johnston led the discovery of the first example of a disc in Keplerian rotation around a forming O-type star, AFGL4176 (Johnston et al. 2015). This ground-breaking work also involved detailed radiative transfer modelling of the continuum and line emission to obtain the properties of the massive YSO. Dr Johnston has contributed to several other ALMA projects to characterise massive YSOs at high-resolution, and if possible, search for discs around them (Cesaroni et al. 2017; Maud et al., 2017,2019; Beuther et al. 2019; Moscadelli et al. 2018; Beltran et al. 2018).

Later, Dr Johnston led follow-up ALMA observations of AFGL4176, at 10x higher resolution, which resolved spiral structure within the disc (Johnston et al., 2020a). These observations bore a startling similarity to the simulations conducted by Meyer et al. (2018), in which we predicted the observability of a gravitationally unstable disc around a forming massive star.

The line-rich spectra obtained towards AFGL4176 with ALMA led to a further study of the chemical complexity within the AFGL4176 disc and circumstellar environment (Johnston et al., 2020b), in which we detected 203 lines from 25 molecules. These molecules fell into several different groups exhibiting different morphology and kinematics, often differentiated by whether they were N-bearing species that traced the disc or O-bearing species, which were mostly blueshifted and asymmetrically arranged in the disc.

Current research interests include investigating the highly-resolved chemistry within massive YSOs traced by ALMA, as well as what this can tell us about the physics playing out in the disc such as shocks. Dr Johnston is also a member of the CORE survey, a survey with NOEMA that studies massive YSOs and the substructure within these regions at high resolution (e.g. Suri et al. 2021, Mottram et al. 2020, Cesaroni et al. 2019, Ahmadi et al. 2018, Beuther et al. 2018). She has also collaborated on several chemistry studies within the CORE project investigating chemistry in other regions of massive star formation (Gieser et al. 2019, 2022).